Build Session 30 : More Fuel and Washer Bottle Fitting

Having left the boot unfinished, after fitting the boot carpets, it was time to get and finish fitting the Washer Bottle and therefore the boot.

Some Fuel

.. but first some fuel. We had put enough fuel in the car to get it started, but it was going to need to be fully filled for the IVA test. So, out with the Jerry can again and a trip to the local filling station.

I used the same old t-shirt to filter the petrol coming from the jerry can into the 1 gallon plastic tank. And thankfully I did, look at the debris left in the t-shirt…

T-shirt fuel filter full of Jerry Can debris

I’ll still need to fill the car to the brim before the IVA (Individual Vehicle Approval) inspection but I can do that with a furtive sneak-drive once the PBC (Post Build Check) is done and I’m ok’ed to drive it to the IVA.

Note: from what I can tell, you can drive a car to and from a booked appointment that is related to getting your IVA passed. I take that to mean that I could technically drive the car to both the PBC and IVA. If I booked a slot at a filling station then I think I could also drive it to fill it up with fuel – but that’s academic seeing as nowhere will do such a booking. It’s also a long way to Williams (15 miles) for the PBC and I’m not keen to drive the car there given nobody else will have checked it for “crazies” that that point.

Washer Bottle Bracket

With the tank mostly full it was time to turn to the washer bottle again. I’d got as far as fitting the fuel filler shroud along with the washer pipe and electors fed through the fuel filler shroud. I’d also got some pointers about fitting the washer bottle in the boot from Derek a few weeks earlier. He had sent me three images of how Caterham do the washer bottle now but their fixing looked a little flimsy to me – a single fixing point – and with a different bracket than the one they’d sent me.

Caterham boot fixing for washer bottle (2017 – Caterham)
Caterham boot washer bottle (2017 – Caterham) – No valve installed, which I’m sure is wrong.

Caterham use a single rear-wing mounting bolt to attach the bottle. I thought I could make up a bracket from extruded bar Aluminium and have a little more control over where the bottle sits on the side panel and that would use the bracket I had got.

I started with some extruded Aluminium bar…

Extruded Aluminium bar used for Washer Bottle Bracket

I then proceeded to reduce it’s depth by grinding off about half of the fins. The bracket is going to fit something like this…

Washer bottle brackets together

And this is how it finished…

Washer Bottle bracket installed

Plumbing a Washer Bottle

[ Note from the future: see the bottom of this post for an update on the washer bottle valve ]

Once the washer bottle was in place I could start to look at adding the tube and electrics to its motor.

The tube that is pre-fitted to the washer bottle is larger in diameter than the tube on the car that is fitted between the windscreen nozzle and the rear of the car. The tube on the car from the windscreen nozzle to the boot is pre-installed by Caterham in the chassis when the car arrives. It was clear in the images provided by Derek though that they use this smaller diameter tube to connect directly to the washer bottle motor.

Therefore, I took off the pre-fitted washer motor tube and cut the tube fitted to the car to the right length (plus a bit to make sure I can adjust it if needed).

So, out with a hair-dryer and heat up the mouth of the smaller tube so it’s soft enough to stand a chance of fitting over the motor nozzle…

Warming up the washer bottle tube to fitter the motor output. Needs a valve adding – see below!!

So in the end it looked like this…

Final washer bottle tube and electrics – but needs the missing anti-dribble valve

That was a simple job in the end. If I did it again I’d make the Aluminium bracket I fabricated a little thicker. But overall I’m happy with how that worked out.

We’re getting to the end of the build now. Doesn’t seem like there are that many things to do. [Note from the future: dream-on!]

2018-04 Update on Washer Bottle Install

So, after running the car for a few hundred miles I’ve realised I missed a component in the washer install.

I think I mentioned elsewhere that when I’d filled the washer bottle and jacked up the rear of the car, I would get a dribble from the washer jets. And under heavy braking there would be a real jet of water gush from the washer jet as water was forced forwards from the washer bottle in the boot to the washer jet on the windscreen.

I kept on meaning to take a look at it and suspected that it was due to a valve that I’d missed from the install. The washer bottle came with a white valve attached to a small piece of tubing on the motor of the washer bottle. The pictures I’d got from Derek showing the new boot install method didn’t have the white valve, so I thought I’d follow Derek’s lead and leave it off – it made the install neater to leave off the valve IMHO.

I couldn’t figure out what the valve actually did by inspecting it. Sucking some air through it seemed to provide some restriction but it didn’t seem to do a great deal. I was sort of expecting it to be a non-return valve for some reason but that didn’t make a lot of sense either.

Anyways, it seemed to me that the missing valve was causing my dribble, and so I duly pulled the hose off the washer bottle and inserted the white valve inline.

Problem fixed.

Now I neither get the dribble when the rear of the car is raised, nor when braking. Here’s the final result…

Washer bottle flow reduction valve installed

Build Session 29 : Rear Wings

This was one of those jobs I’d not been looking forward to. Definitely not a “bolt them on an forget them”. The rear wings were going to need some fettling… and expensive-to-replace fibre-glass fettling at that!

The car arrives in its kit form without the rear wings attached. They’re a big part of the aesthetic look of a Seven but they’re large fibre-glass moulded parts and unwieldy to handle and expensive to replace if you screw up either attaching them to the chassis or fitting the stone guards that are essential to stopping the wings getting trashed by stones being thrown up from the front wheels.

Without the wings the rear wheels look like this…

A nude rear wing, devoid of its wing wrapping.

There were a number of options for the rear wings when ordering the initial kit: the main ones being:

  • fibre-glass vs carbon and
  • stone-chip-guards vs chrome-guards vs no guards.

The cost of going carbon for the rear wings didn’t seem to be worth the expense (for me). I wasn’t keen on the “carbon” look of the rear wings and the weight saving for the occasional track day didn’t seem worth it.

However, I’d been advised that stone-guards are essential. Stones get thrown up by the front wheels and will directly target the rear wings. The stone guards are theoretically sacrificial plates that sit on the leading edge of the wing and can be replaced for a lot less cost than a whole rear wing. Now… I had been a little aesthetically concious with the front wings and spec’ed them in carbon… so I went for carbon stone guards instead of chrome… The “black pack” you get with an R spec car and the carbon front wings seemed to work better with carbon rear wing protectors. I hope that all makes sense.

Anyways, the task today is to get the wings to fit the car (no mean feat) and then the wings need to be drilled for the stone guards to be fitted. Again, that’s lots of fettling to an expensive fibre-glass component (did I mention that already!).

Bane Getup

My first task today was to get me ready for cutting, dremeling and drilling lots of fibre-glass, a cross between Batman Bane and Darth Vader…

Breathing and eye protection from fibre-glass dust

With this protection I found that by the end of the day my lungs still suffered from residual dust in the air. I also found my eyes weren’t protected as well as I’d hoped, probably again from residual dust, and were sore for a few days. I would recommend goggles rather than the glasses I wore.

Radius Arm Slots in the Wings

Like most of the car before it, I started on the RHS first – I have more space on the right in my garage and can spend more time pondering options in that space.

The first job today is to turn a hole that’s pre-cut in the wings for the radius arm, into a slot. It is possible to avoid this by taking the radius arm off, fit the wing and then re-attach the radius arm. That sounded like a lot of work and I also thought I was likely to need to take the rear-wings off again. It seemed easier just to cut the slot and have greater flexibility on wing fitting/re-fitting. That seemed to make sense to me anyway. The radius arm can be fitted in one of two configurations and I may need to take the wings off at a later stage and “slot” the other hole in them for the other configuration option.

For those confused, the RHS radius arm is the black steel bar marked in green pen with “TORQUE” in the image of the rear wheel at the top of this post. I’d marked the arm with TORQUE to remind me they needed torquing once the weight of the car was on the ground or at least on the De Dion tube. The wings are pre-cut with two large diameter holes in the side flange so the radius arm can be connected through them – you can see one unaltered hole in the image below.

Need to turn a hole (as in top of this picture) into a slot (as in the bottom of the same pic)

I had three or four goes at creating the slot, making it wider each time, and ended up with something around this size…

Radius arm wing slot ended up this big

The slot seemed a bit excessive, and reduced the rigidity of the wing at that point, but the manual says that that’s ok because it’s going to be well secured to the bodywork and won’t make a difference once in place. I managed to make a smaller slot for the LHS wing when I got to that later in the day.

Testing out the Wing Fit

Now I could temporarily tack the wing to the bodywork and see how it hung. That allowed me to visualise where all the trim piping would go and where the stone guards needed to sit so there were no gaps and they didn’t interfere with the fit of the wings.

I found that not all of the wing mounting holes lined up with the bodywork. So… Out with the dremel again and fettle those holes. I found the RHS wing worse in this respect than the LHS wing… though I’m fully open to the fact that I was more prepared to “persuade” the LHS wing into position at that point in the game.

I applied masking tape to the wing where the stone guard would sit, again allowing me to visualise things better…

Masking tape helped me see where the stone guards were going to go

The next problem I had, in the little space that was available to me, was how to hold the rear wings as I worked on them. Cutting the radius arm slot allowed me to place them on cardboard on their side, but the stone guard fitting seemed to need to have them upright. It was also due to rain today (and it did) so I wanted something portable. The solution was staring at me…

A wheels good jig

Of course I had to be careful not to drill through the wing and into the tyre, but I managed that ok through the day. What I was less successful with was not scratching the wheels. I’d put cardboard down to protect them on the floor but managed to drop one of the wheels onto the stone floor and scratched it – bummer!

Drilling the Wing for Stone Guards

I’d been prevaricating enough now… time to get the drill out. The guards need to sit hard up against the edge of the wing, so I added a straight edge to help me…

Straight edge helping me line up the stone guard to the wing

I could then clamp the stone guard to the wing…

Stone guard temporarily clamped to the wing

These carbon stone guards are pre-drilled with the holes needed to attach them to the wings. So, once I had the guard where I wanted it, I just needed to use my paint-pen and mark through to the masking tape below. On reflection I may have got the stone guard a little low on the wing. The trim protrudes slightly below the line of the wing as I have it. I’m not unhappy with that as it will protect the lower edge of the wing better than how I think Caterham suggest you do it. My only concern is that it might be an IVA issue. [ Note from the future: turned out not to be an issue at all for my test]

There’s another complication to get right here now too. You have to sandwich some trim piping in between the stone guard and the wing. Both the trim and the wing need to have holes drilled or cut into them in exactly the right place. The trim also needs to have “v”‘s cut into it so it will fit without puckering when sitting between the wing and guard.

I found that if I clamped the trim behind a stone guard…

Clamping stone guard trim to stone guard

Then I could also use my paint-pen to mark where the holes needed to be…

Paint pen used to make where holes need to go in stone-guard trim

I also marked the trim where the v’s needed to go. I used my leather hole punch to cut out the green dots I’d made…

Cutting out the stone guard trim with a leather hole cutter

Once I’d done, the trim looked like this…

Stone guard trim with v-shaped cutouts and holes

Then I could drill out the wings…

Drilling the wings for the stone-guard rivets
All the holes drilled

Just need take off the masking tape…

Masking tape taken off from rear wings

And rivet them in place, not forgetting the trim sandwich…

Riveting a stone guard onto the rear wing

It was at this point that I was regretting not spending some more time on my initial plan of rivnuts. The rivets were going on with a rivet shearing force that was creating dimples in the stone guards. I’d feared this happening but I’d gone with rivets instead of rivnuts and this was my price.

I’d seen people use rivnuts instead of rivets to attach stone guards. In the end I didn’t feel confident in drilling a bigger hole for the rivnuts than the rivets needed – that was a one way street, I could go from rivets to rivnuts but not the other way around.

I also considered cutting oversized holes in the stone guard trim and fitting nylon or plastic washers so that the rivets didn’t pinch the sandwich into a dimple. However, the washers I’d bought were too thick and the sandwich wasn’t going to work. I should have mocked all this up with some offcuts of everything and then I’d have been more prepared. However, I was a long way into the wing install today and wanted to get it done while the weather was ok – I needed to do the fibre-glass stuff outside.

In the end I carried on with the rivets and will submit to IVA with them like this. I’ll add the “switch to rivnuts for the rear wings” to my future project list.

It’s then a simple-ish case of bolting the wing to the bodywork using a combination of bolts into existing rivnuts and bolts/nuts.

You can see the dimples clearly on the fully installed stone guard and wing.

Wing, stone guards and various piping installed. Not happy with the dimples

This job, like so many others, proved again that its quicker to do something a second time. It took me something like 4 hours to adjust and fit the RHS wing. It then took me around 2 hours for the second wing. I think that speedup was the same for all of the jobs. In the end the left hand side of the car got done much quicker than the right!

I was pleased that I managed to get the wings onto the car without trashing either of them. I hadn’t put the stone guards on the wrong way around and I hadn’t slipped with the drill anywhere. I hadn’t drilled holes in the wrong place or on the wrong side of the wing, or put the wings on the wrong way around. From that perspective and the fit and finish I managed on the wings, I’d give myself a 9/10. However, I was not at all happy with the dimples on the stone guards and they will have to come off again at some point – 3/10.

A long but successful day today that I wasn’t really looking forward to. Yet one that has completely transformed the look of the car!

Build Session 28 : Boot – Floor, Fuel Filler Shroud and Carpets

Ok, so now I’m happy that the engine is running ok and the coolant system is doing its job for the moment. Now onto some more cosmetic stuff at the rear of the car.

Boot Floor

For such a well put-together kit that Caterham produce, the ply-wood boot floor jars a little. The cover for the fuel tank, that takes up about half of the boot floor, is a lovely piece of sandwiched honeycomb aluminium sheet. Yet the remainder of the boot is taken up with a flimsy piece of unfinished ply-wood.

Unfinished boot floor ready for some yacht varnish

I’ve seen a number of people posting on forums about why Caterham have left this section as Ply. They say it could be crash protection or so it doesn’t squeak behind your ear. I’m more inclined to think its cost saving or that the x-mm of plywood fits nicely in the slot and anything else would require re-engineering of that boot section. Whatever the reason, it still jars.

The bottom of this wooden floor section sits above the differential and is therefore exposed to the elements – spray, stones, etc kicked up from the road. I therefore wanted to make sure it was protected and yacht varnish seemed like the ideal choice. I sanded…

Sanding the boot floor

Then varnished the ply-wood twice…

Varnished the boot floor with two coats of yacht varnish

I was using bench dogs to make sure I could varnish both sides without having to wait for one side to dry…

Bench Dog Tools

With the boot floor out you can see the diff and handbrake adjuster…

Diff exposed and handbrake adjuster (right) with boot floor removed. The fuel line is running on corrugated pipe at the top.

… and the rear flexible brake hose fixings…

Rear flexible brake hose also visible with boot floor removed. I hadn’t added any 5/16th hose to the brake pipe at this point.

Boot Carpets

With the varnish on the boot floor drying it was time to turn my attention to the boot carpets. Yes, I know that’s completely non-essential part of the “real” Caterham experience but I was more interested in their sound deadening properties than their aesthetics.

My weapon of choice for the carpets was the spray adhesive as used on the cockpit carpets…

Contact Adhesive

And seeing as I’d be spraying in and around the boot I decided to apply masking tape to anything that didn’t move…

Protective masking tape and cardboard applied to the rear of the car prior to spaying contact adhesive for the carpets

Fuel Filler Pipe Shroud

At this point I also decided that I needed to make sure the fuel filler pipe shroud would fit with the carpets installed.

The fuel filler pipe runs from the fuel filler on the right rear of the car, into the boot and down into the fuel tank. A shroud covers the pipe and I guess gives an extra layer of protection so that something rattling around in the boot can’t puncture the fuel pipe and expose fuel fumes to the boot and it’s occupants.

Fuel filler pipe and washer fluid pipework/electricals coiled

It seemed that it made sense that the fuel shroud fit directly to the aluminium fuel tank honeycomb and that the carpet sit on top of the shroud base flanges.

Fixing the shroud directly to the boot floor

The shroud would fit snuggly in-between the boot floor and the boot top chassis rail, but it was a squeeze. And unmodified, the shroud didn’t sit as far back towards the body skin as I’d like.

I pondered this for a while to see if I was doing something wrong, but in the end I decided the only way to make it fit properly was to take some of the aluminium off of the top of the shroud. After a few “offering’s up” and some “paint-marker’ing” I decided 4mm needed to come off the top…

4mm needed to come off the top of the fuel filler shroud

And once it had been cut and the IVA trim had been added, it looked like this…

Fuel filler shroud with its IVA trim added.

At some stage I’m going to need to get the washer bottle attached to the side of the boot and run the washer fluid pipe and electrical connections through the fuel filler shroud…

Washer bottle eventually needs to be fitted to the side of the boot

For the moment I just need to worry about getting the pipework and electrical through the fuel shroud, I’ll worry about connecting them to the washer bottle when I’ve figured out how to attach the washer bottle to the bodywork side skin and then I’ll know how long to make the pipe/cables.

However, even at this stage the washer bottle electrical connection didn’t seem to have enough length left in it to get to approximately where the washer bottle would go. So I cut the cable ties down the side of the petrol tank and re-arranged them to give me more cable to play with…

Re-arranging the washer bottle electrical cable

Next up was to drill holes in the fuel filler shroud to take the washer fluid tube and the electrical connection. I used a hole punch to mark out where I wanted to the hole and drilled a 9.5mm hole to fit exactly the grommets I had…

Box of grommets, I used ones from tray one tray in from bottom left

I used 13mm OD / 7.5 ID (which need a 9.5mm hole) grommets but I think eventually I did find some grommets in a bag that should have been used for this job. The washer fluid tubing has an OD of around 6mm.

The grommets looked like this when they were fitted…

Grommets for the washer fluid pipework/electricals in the fuel filler shroud in place

I also needed to get the electrical connections through the grommet…

Washer bottle electrical connector

… which was simple once I’d taken the electrical connections out of their shroud and passed them through the grommet.

I’ll leave fixing the washer bottle to the inside of the boot until all the carpets are in place… and I’ve figured out how to actually fix the washer bottle.

Back to the carpets

With the fuel shroud figured out I could fit the boot carpets.

I was going for a permanent fixing, so applied contact adhesive to both the carpet side and the bodywork side…

Adhesive applied to both carpet and bodywork

I held the carpet in place to cure with plywood and clamps…

Mocking up using plywood and clamps to hold carpet in place while the adhesive “went off”. In the end I actually cut a 45 degree chamfer on the inner plywood as you can see in this picture that it fouls on the body work.

I was pleased with the side carpet installation…

Boot side carpets installed

There didn’t seem to be any option but to cut the rear boot carpet around the fuel filler shroud…

Cutting the boot rear side carpet so it fits around the fuel filler shroud where it exits the back of the boot

Fitting the carpet around the fuel filler shroud was a bit of pain where it meets the boot floor. I couldn’t find an easy way of deciding where to cut the boot floor carpet. In the end I eyeballed it and got it a bit wrong. Maybe I’ll buy a piece of carpet to fix that some time in the future but it looks perfectly ok until you look closely. What I should have done is create a cardboard template, but I was running out of time and a little bit of patience at this point in the day and rushed it 🙁

I decided to leave the boot floor carpet floating and not to glue it in place. I reasoned that I might need to get access to the diff or brake lines from the top later on. [Note from the future: I did]. I also left the floor carpet a little big. It didn’t seem to fit correctly in the end but I decided to let everything settle before I see how much I need to trim it by. So… you can see it’s rucked a little in the image below.

Boot carpets done

Aesthetic note: I actually quite like the green against the Purple… I wonder if that could be the accent colour for any bonnet/side stripes I add later.

Shroud in place with washer tube and electrical cables coming through grommets
LHS of boot with carpets installed

That’s the boot carpets done. Still need to fit the washer bottle properly but that’ll wait for another day.

Build Session 27 : More Bleeding Coolant

It was going to be “back to the coolant system again” today. I had left the car at the point where we’d started the engine but were worried about the coolant temperature getting well over 100C, something like 105C. We then chickened-out,  turned it off and decided to ask Derek.

So I emailed Derek and this is the thread we got into…

Temperature Email thread to Derek

Hi Derek,

  we managed to get the engine going on our build at the weekend. We had a bit of a problem with the inertia switch (even after resetting it and hearing it click) but once we’d taken it off and “had a look at it”, it all seemed to work from then on.
  Anyway, question: we’re finding that the car is getting to over 100C when sat in the garage – light revving but obviously no load. The radiator is getting mildly hot at the top but not at the bottom, implying we probably have the thermostat slightly open. The heater is pumping out hot air when we open the valve and turn the blower on. All other pipes seem to be getting as hot as they should.
  Is this normal and we just need to let it get up to 110C or something before the thermostat opens fully. I’ve heard Duratec’s run hot anyway and the standard Caterham shipped thermostat only opens at over 100C.
  Also, the fan is not running at that temperature. We’ve isolated the fan and hooked it up to 12V, and it runs fine.
His response:

Hello John,

Sorry I haven’t got back but I was off yesterday, it sound like you have an airlock in the system, when you filled the system did you remove the bolt on top of the rad as this can help, the fan will not come on until the temp is around 100 anyway.

Kind regards

I sent this by way of response but didn’t get a comment back… wasn’t really expecting one…

Thanks Derek, I thought you might have been off.

Yes, I removed the bolt on top of the engine and let fluid run out of it. It certainly feels like I have an air-lock but I can’t put my finger on it at the moment. I’ve removed a few of the higher pipes and haven’t got it yet. My next plan was to take off the bottom radiator hose next to the thermostat in case there was air just before the thermostat. After that I’m not sure what to try but I’ll get there. I just needed you to say it sounds like an air lock and I’ll keep going.
Any news on the bonnet?
At this point I was also chasing the resprayed bonnet being sent back to me.
As well as asking Derek about the temperature I also posted to the private Facebook Caterham Tech-Talk page. I got some suggestions that I should check the coolant temperature as reported to the ECU by the sensor on the rear of the cylinder head. This one…
Cylinder Head Rear Temperature Sensor


So I went and bought a cheap OBD-II data scanner from Amazon (AutoLink AL319). It also does fault reset stuff but I’m not so interested in that at the moment.

This is the first of 11 screens the OBD-II reports, I’ll do a bigger post on OBD at a later date… when I’ve got some real data from it and some miles under my belt. The OBD port is under the dash, cable-tied to the steering column assembly.

OBD-II Screen showing ECT (Engine Coolant Temperature) while engine off and cold

On a quick fire-up of the engine the OBD gadget was reading about the same as the analogue dashboard gauge.

Long story long… this got me to the point where, today, I could start to have another look at whether I had a coolant air-lock. Even with Derek’s re-assuring words I had not had the fan cut in or the thermostat open yet and before getting the car up to temp again I wanted to make sure there were no air-locks and I was performing a good test.

Throttle Pedal Position

But before that, I started the day off with a simple job… setting the throttle pedal position. My reasoning being that if I had to have the car running for a period then I might end up sitting in it keeping it ticking over. Having the throttle pedal working would make sense. I had already set the tick-over the previous weekend when we ran it up for the first time, so that didn’t need to be looked at again.

Jam a philips/posi screwdriver down the end of the pedal and yank-to-fit (TM).

I then “yanked-to-fit ™” the pedal with a philips screwdriver inserted down the shaft of the throttle pedal until the cable in it’s slack position just fit snuggly into the throttle pedal. I had made sure that the cable, when slack, allowed the throttle to be fully shut. And at the other end of the scale I made sure that pulling the throttle cable so the throttle was fully open meant that neither the lower or upper throttle pedal limits came into play. I set the throttle pedal position, by bending the shaft, so it “just” created some positive tension in the cable… i.e. it wasn’t slack when fitted, nor did the pedal pull the throttle open at all.

Coolant Air-Lock Hunt

 So, on with the hunt…

We’d looked at most of the places we thought there might be an air-lock the previous weekend but I wanted to go through them again and spend some more time on it.

First up was to see if there was anything locked around the heater pipework. This is the highest point in the plumbing system and therefore I thought naturally somewhere air would collect. However, my hunch was that, if anywhere, there was an air-lock around the rad-bottom-hose or thermostat but I wanted to start with the simple stuff first and not have coolant everywhere.

Checking for air-locks and refilling coolant around heater pipework.

Next up (or down) I lowered the rear of the car to see if I could shift any air-locks that way.

Nose up, rear down… chasing air-locks.

I also tried the other option, nose down, rear up.

At this point I decided to fire the engine up again and see how I was getting on letting it get up to temperature.

The primaries were all getting equally hot and the head to around 180C…

Primaries and head getting up to temp.

The gauges were reading about 103C when finally the top radiator hose got properly hot…

Gauges at the point the top radiator hose got hot and the thermostat was therefore open

Then the fan kicked in at around 107C…

Fan started up at around 107C

Oil cooler was showing around 85C at the point the fan cut in…

Oil cooler at around 85C at the point where the coolant fan cut in

It’s also interesting that the 5/16th hose from the rear of the cylinder head is pumping coolant to the header tank…

Ok…. So… now everything seems to be running ok. The thermostat seems to open just over 100C and the fan cuts in at around 107C.

… but I hadn’t really done anything. There had been no sign of any air-locks in the heater pipework and no sign of any air when I’d pulled various hoses off and put them back on again. There was also no drop in the coolant level in the expansion tank as I jiggled the front and back up and down (which might have indicated air moving into the expansion tank from the pipework). In the end I think we just weren’t brave enough getting the engine up to temp.

Having done a bunch of research on the Duratec engines, this seems about right. The high running temp is meant to help emissions and the coolant system is clearly set up to be pressurised at over 100C.  While I’m not so worried about emissions I worried that the cooling system is up to its job.

Another Email to Derek

I then spent a few days doing some more in-depth research into the coolant system and created my build session 17.5 post along with another email to Derek.

Hi Derek,

  I got the engine running for an extended period today. Its sits at about 105C on the temp gauge. At a steady tickover the thermostat is open and the fan cuts in an out to regulate the temp. Does that temp sound right? In the end I don’t think there were any airlocks. I did a couple of hours trying to find air in the system before leaving it to run for long, but in the end I don’t think there was much in there (I’ve done a lot of plumbing along with bleeding air out of old bangers, so reasonably familiar with air locks 🙂 ).
 I’m wondering if the thermostat might have stuck on for the first run and perhaps thermal cycling it got it going? Is that likely or something that happens?
  On the way to getting the water sorted I did a lot of research this week on the water systems on Duratecs. I did a bit of an in-depth (that might be an understatement) blog post on it. Complete with animated 3D renderings! I’d appreciate you giving it a once over if you have time. It might also be something to point other people at if you feel the editorial is good enough. Feedback appreciated. The blog post is here:
Derek’s response was a little concise but I took it to mean there was nothing wrong with the temperatures we were seeing…


Hello John,

Your animation is very good and everything looks to be going where it should be, I might use this myself.

Kind regards

Here’s my coolant system model again in case it helps to be on this page too…

Now, the big question is whether this running temp is too high for normal operation, let alone track days. Will high load mean we get thermal overrun when we stop after a track session and the fan is unable to keep the temperature down?

The only controls here are to a) fit a lower operating thermostat (85C) and/or b) add a bigger, higher capacity fan. The worst case appears to me at the moment would be after a track session and then sitting the car still with no airflow over the radiator – only the fan cooling the system. In this scenario I don’t think it will make much difference having the thermostat set to 85C vs 105C. The coolant will be getting to a high temp anyway and if the fan isn’t big enough to take the excess heat away from the engine then it won’t matter a great deal about whether it starts at 85C or 103/5C for the thermostat to open. On the fan size, sure that might help if there’s thermal overrun but I’m not planning to to change that at the moment. I guess there’s a third parameter here, potentially the fan operating temp could be set differently in the ECU, but that would need an aftermarket ECU – to my knowledge you can’t change anything like that in the Caterham ECUs. Again, just having the fan cut in earlier probably won’t make a big difference to things if the whole coolant system can’t cope with the track-load-and-stop scenario…. temperatures will run away no matter what. I presume this is all part of Caterham’s design thinking so I’m not too worried that I’m going to get into trouble with my initial light road use or even a timid first attempt at a track day.

I’m also wondering if a Duratec runs better when its hot or when it’s not so hot. I see lots of posts on forums where people switch out the factory fit thermostat for an 85C “race” thermostat. It’s not obvious whether this is for 2.0L Duratecs, wet or dry sumps with oil coolers, etc etc. Does having an 85C thermostat mean you get to a temperature equilibrium at a lower point than with a 105C thermostat? Is there thermal runaway and having an 85C stat mean you can run longer as the runaway builds? There’s clearly also a thermal gradient set up from the radiator all the way through to the internals of the block and head… does having an 85C thermostat mean you get a more optimal temperature in the block/head than when running a 105C thermostat at high load??

I’m new to this level of theory around engine running temps. Clearly you don’t want temps so high that you get pre-ignition or fueling problems on the inlet side (though running injectors is probably going to be easier than having a carburettor setup – due to increased fuel pressure?? – that’s a guess). And clearly there will be a point where the pressure release valve on the expansion tank will operate and possibly cause boiling in the system as pressure drops. I’ve heard stories of cylinder heads eroding due to micro-boiling where hot spots are created due to insufficient coolant flow… that needs more research too.

Hmmm. Lots to think about. My natural inclination is to put sensors everywhere and grab some real time data – but that’s another project.

Something to keep and eye on then, but for the moment I think the coolant system is working as intended. We need to be getting on with some more of the cosmetic stuff now…

Build Session 26 : Coolant Bleeding – Unproductive

After the euphoria and relief of getting the engine going yesterday we thought we’d have another look at what might be causing the coolant temperature to get so high. We only had an hour or so in the morning but couldn’t resist another look to see if we could find any obvious air-locks. Little did we know at this point that the coolant temperature was supposed to get that high (105C is normal), but we weren’t taking any chances.

We played around for a while, attempting to bleed air from the system: heater connections, rear of cylinder head, thermostat T-piece and radiator top hose. There didn’t seem to be any air in the system from what we could tell and due to a lack of time decided again to consult with Derek and see what he said in the morning.

Three wise monkeys reviewing the coolant system

At the end of our efforts the engine bay still looked like this…

Engine bay the day after first start