COX GTM running too hot.

[AndyB72]

Help... I'm having a problem with the car running hot and instantly boiling when the engine is turned off. Mark came over and set the timing so that should be fine. The 74 deg thermostat is working fine and once open water is flowing into the header tank and I assume around the system. I've bought a temperature gun thing and when heated up and stood in the garage with the electric fan on I'm getting 80-90 deg on the cylinder head, 60 deg at the header tank and 40 deg at the radiator, there is very little change in temperature across the radiator. When driven on the road the temp the temp goes to 90+ and sits there.

The car doesn't have a heater and I'm getting water coming out of the bleed tube on the radiator.

I'm running a mix of water wetter, water and antifreeze

I checked the temperatures on my 1100 Mini and that has 70+ at the cylinder head and drops 20 deg from top to the bottom of the rad.

Photos of the build and pipe routing can be found on this thread...

viewtopic.php?f=6&t=8731

[GTM71]

Cooling.JPG

Andy
Is this your layout? It sounds to me like you might not have enough resistance. A swirl pot might help.
Also is the hose route going from bottom of pump to top of rad, then bottom of rad back to top of engine?

[GraemeC]

On Rich's it had 2 header tanks - one down by the rad too. I think this was because he'd had problems bleeding it.
May be worth dropping him a line (if his 'beardy senses' don't mean he's already read the thread!)

[AndyB72]

This is the layout of my car...

Cooling.jpg

[Exminiman]

Just a thought, might be worth adding an electric water pump and some in- line stats to control speed and on/off.

Trying to predict how water will move almost naturally around a system like this is going fraught with problems.....


https://www.demon-tweeks.com/uk/search/ ... er%20pump/

[surfblue63]

Did you put in a larger water pump (MiniSpares EVO), because with all the extra pipework for the front mounted rad, the pump needs to do extra work to overcome the resistance of long pipes and the header tank.

From the temps you've measured it does suggest low flow in the system.

And I'm sure you've had the cap off the header tank whilst running to make sure the head gasket is not leaking and air locking the system.

Also Exminimans idea of an extra electric pump sound like a way of overcoming the extra resistance in the system.

[GTM71]

A water pump is a very effective mover of fluid, I would be surprised if its struggling to move the fluid around. More likely is a air lock somewhere or cavitation because of a lack of resistance. I remember when My Father and I built our first racing Fairthorpe it overheated all the time, we thought it was an air lock for ages until a Ex F3 mechanic told us to try adding a swirl pot to the top hose and hey presto no more overheating! Header tanks don't act in the same way as a swirl, they are generally for getting ride of air and add little resistance. Just a thought, I'm no expert!

[AndyB72]

I've fitted the new MiniSpares EVO pump. I've also run it with the cap off and there are no bubbles coming up so I assume the head gasket is ok but I'll do a compression test.

An electric water pump was one of the things I was considering, I know the Car and car Conversions GTM uses one, but I think that was down to the temperatures his engines was pumping out when it was turned off after a good hammering.

[Exminiman]

I've fitted the new MiniSpares EVO pump. I've also run it with the cap off and there are no bubbles coming up so I assume the head gasket is ok but I'll do a compression test.

An electric water pump was one of the things I was considering, I know the Car and car Conversions GTM uses one, but I think that was down to the temperatures his engines was pumping out when it was turned off after a good hammering.

With the rad and engine far apart you are also fighting the effects of hot water waning to rise, suitable placed inline electric pump will make sure the water circulates. in-line stats make sure that the pump speed relates to the temperature, and so is moving cold water or is not moving hot water.....

[IvorBiota]

This is the layout of my car...

Cooling.jpg

I think part of the issue is the pipe from the heater valve outlet on the cylinder head. This should be routed to the header tank so that any air in it at startup is removed.

From the engine photo, it forms an inverted “u”, perfect place for air to gather when everything has cooled down. As this pipe is used as the thermostat bypass, this is where the water (and any air bubbles) is drawn from when the engine is started down.

PS Great project, just needs to go as well as it looks.

[Oneball]

How full is your header tank when cold? Are the hoses below the level?

How much volume have you got for expansion in the tank?

I’d have run the head outlet straight to the rad and kept it lower than you’ve got it with a tee and pipe to the expansion tank so thats the highest point.

Have you checked for blockages in the rad and or pipes?

How clean was the block? I’ve blocked a rad on a newly built engine with crap that’s come out of the water ways and I’m not a fan of water wetter it’s kind of sticky.

[Cheeser]

I don’t have a Cox GTM but I do have a Davrian Mk8 with 1380 mini engine, which is used on the road, track days and a few hill climbs a good many years ago, I have not experienced over heating except briefly before getting rid of air locks.
It has a ducted front mounted Mini Spares 2 core rad served by 25 mm aluminium pipes.
Flow comes from the 82degree stat into the top of a high mounted swirl pot (which is plumbed to an expansion tank 13lb cap), then from bottom of the swirl pot to the top of the front mounted rad. Bottom of rad via the 25mm pipes to a standard water pump.
Using the car on the road and wet days on track I decided to fit a heater, so this is plumbed with 15mm pipe from the heater tap on the head to the heater, then from heater into a tee in the 25mm return from the rad which as stated goes back to the pump.
This setup works for me!
Thoughts….
1. get the swirl pot as high as you can, and fit a swirlpot rather than just a tank.
2. Jack the back of the car up as high as you can when filling the system.
3. You may need to bleed at the top hose on the rad.
4. Use straight forward antifreeze, as weak as reasonable .. 25% ?
5. Yes I agree that the arrangement of plumbing from your heater tap into the system may not be helping, try disconnecting and give it a try, although in principle I think it should work and it encourages flow through the head if you leave it open!
6. I don’t believe an electric pump is necessary unless there is a basic problem or you’re trying to gain a few bhp !
7. I did fit a larger rad but found it total overkill and more weight, there’s plenty of additional volume in the pipe work to the front mounted rad!
8.There are other Mini engined Davrians successfully operating with the same basic layout.
9. Obviously there could be other fundamental problems with scale/ blockages but I’m sure you’ll have already sorted that.

Good luck

[AndyB72]

Thanks for your replies all I'll keep you posted.

[hanlminiman]

Get in touch with Derek W of CCC GTM fame.

[Peter Laidler]

If it IS an air-lock, would it not be possible to plumb one of those little radiator air-lock bleed valves into the highest part of the cooling system. Air will always migrate to the highest part of the system - it's a law of physics. Just open the key, vent and that's it. Just like I have to do with the highest radiator in my house once a year. Or am I missing sumfink.....?