Diagnosing over-heating on a k series

[Irrotational]

I know this is now almost a 30 year long topic, but I am having trouble with my car. I've read many threads in the past, from fillling via the heater hose, to winching the front super high with an engine hoist...but is there a guaranteed way to avoid airlocks?

Also are the symptoms below an airlock, or something more sinister?

After 2 or three minutes of tick over the hoses on the non-exhaust side get hot, and hot water goes up to the heater and back down the exhaust side to the radiator. I can feel those hoses get hot.

The radiator got hot, across the whole rad, although the final inlet hose on the exhaust side seemed to have a suspicious cool spot on it.

Water temp was reading 80 to 90 through out - didnt sky rocket.

Water starts "pulsing" from a small hose from non-exhaust side of engine back into the top of the expansion tank. Expansion tank slowly fills and then after another couple of minutes water starts escaping around the cap.

Shutdown engine!

The engine has just had its head gasket replaced (not by me) and i was assured that it had been filled/bled properly...but after that I dsocvered one of the apollo hoses was leaking oil and the ECU was toast....so the engine has never really run once HG work was done. I have fitted new apollo hoses and the emerald ECU..so now the engine starts and runs!! BUT i am back to overheating.

I'm just paranoid the HG was not done properly or something...but I'm hoping its "just" an airlock sitting between me and life on the open road.

[jeremyc]

Is your radiator fan kicking in (assuming it's an electric one)?

Also, you might want to look at replacing the expansion tank cap - if it's not holding pressure then you'll get water escaping as you've seen.

[Tupwood]

Does the engine shutdown, or do you turn it off?

I've not had any airlocks in my K-Series (yet) and my refill method ie to jackup the front, and fill from the heater hose… very slowly.

Could the change to Emerald ECU be part of the issue here?

[Tupwood]

or you could add one of these…

https://www.sevensandclassics.com/online-shop/p/re...

which allows for easier bleeding and better temperature monitoring.

[Irrotational]

jeremyc said:

Is your radiator fan kicking in (assuming it's an electric one)?

Also, you might want to look at replacing the expansion tank cap - if it's not holding pressure then you'll get water escaping as you've seen.

The radiator didnt kick in as the water didnt seem to be getting that hot.

I'll order a new expansion cap from caterham.

Edit - caterham don't have any - or they're for a newer round style tank. I have an old square one. Apparently origina square one is EAP8713, and i'm hoping the cap that goes along with it is the PCD100160...ordered it from a random company called Discount Rover MG Spares, but RimmerBros also sell it was an "A" at the end of the model number

Tupwood said:

Does the engine shutdown, or do you turn it off?

I've not had any airlocks in my K-Series (yet) and my refill method ie to jackup the front, and fill from the heater hose… very slowly.

Could the change to Emerald ECU be part of the issue here?

Sorry - bad choice of phrase - I just meant that I turned it off. I think the ECU is fine as it's running the engine no problem.

Tupwood said:

or you could add one of these…

https://www.sevensandclassics.com/online-shop/p/re...

which allows for easier bleeding and better temperature monitoring.

OK thanks - I'll have a look at that too - will see what the fitting instructions are like.

Edit - then I find thread like this that talk about all sorts of layouts, plus there was an article in LF a few years ago with a "MUST DO" mod on the coolant system*...so then I have no idea how the layout is even supposed to work.

Loads of great knowledge but i just want one view on how it SHOULD be.

https://www.caterhamlotus7.club/forum/techtalk/k-s...

• it was an article where someone had spoken to the original k series and metro engineer and they suggested a mod to make the whole loop work better and avoid thermal shock when the thermostat opens.

Edited by Irrotational on Monday 1st May 13:13

Edited by Irrotational on Monday 1st May 13:30

[Irrotational]

I'm sure there will be more twists and turns but a new pressure cap seems to have sorted it!! Coolant stayed where it is supposed to, hoses got hot in right order, radiator got hot then the fan kicked in!

V excited to have a car that can at least idle. Maybe I can even drive it!?🫣🤔😂

[jeremyc]

Irrotational said:

I'm sure there will be more twists and turns but a new pressure cap seems to have sorted it!! Coolant stayed where it is supposed to, hoses got hot in right order, radiator got hot then the fan kicked in!

Glad you got it fixed, and the answer was relatively simple.

[Irrotational]

jeremyc said:

Glad you got it fixed, and the answer was relatively simple.

Yeah thankyou!

A lot more twists and turns through 2023 but this definitely worked at the time!

[Turn7]

For future reference, use Redline for Caterham parts….

Chris Mintoft carries a lot of spares for older 7s as well the modern stuff.

https://www.redlinecomponents.co.uk/

[brums evil twin]

Hey mate (thanks for the email, will reply to it properly)

But another thought - my K series over heated last year, managed to pull over and it boiled up and I lost all the coolant. Re filled but it kept pulsing out like yours. Ended up with the AA and he like me could not get it to settle, he thought blocked rad but it just had a brand new rad. So we could no figure out what it was.

Turned out there is a one way (ball bearing) valve / restrictor - to / from the head which had got stuck closed. Apparently they rust up. Might be worth having a look at that too.

Just got mine back from that fix - first drive on Saturday, now great coolant flow and if anything it might be over cooling, but that's an easy fix with a bit of something to block some of the airflow