Now this is a curiouis one...Coolant over pressure and overheat....

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ant just a few thoughts for you to ponder. was there any over pressure? when you tried the sniff test? have you still got the stat out? maybe its only when at max temperature it releases the pressure. or is the pressure coming at lower temperature? also i should imagine with your petrol mode and the pressure problem you are not allowing the revs to go very high? could it be happen when the revs go higher? i had a cracked head in an escort many years ago that would only release the pressure at high revs. one last thing is there any pressure when you remove the oil filler cap?
 
johnsteele said:
ant just a few thoughts for you to ponder. was there any over pressure? when you tried the sniff test? have you still got the stat out? maybe its only when at max temperature it releases the pressure. or is the pressure coming at lower temperature? also i should imagine with your petrol mode and the pressure problem you are not allowing the revs to go very high? could it be happen when the revs go higher? i had a cracked head in an escort many years ago that would only release the pressure at high revs. one last thing is there any pressure when you remove the oil filler cap?
Click to expand...
Hi John,

Thanks for your thoughts....

There was no over pressure during the sniff test, the stat is still out and has continued to over pressure even with that out.

Even on Petrol she still gets a hammering now and then with high revs and fast running.

No pressure from the oil cap and no 'mayonnaise' either.

Curiously, and this is where I am heading at the moment is during running and immediately afterwards, the coolant is at normal level, this is proved by removing the cap after a long run and there is no excessive hiss nor is the coolant level over flowing the tank.

BUT, This is what I think may be happening, as she cools down the contraction of the coolant is drawing air into the system from a split hose, crack coolant/heater manifold on the back of the engine......then when I run her again, this creates an air pocket which works its way up to the top of the rad and sits there. this causes the level in the expansion tank to rise and over flow blowing coolant out when the air pocket gets hot and expands.

This I can assume, explains the reason why when you open the bleed screw the level in the tank drops as the air is expelled through the bleed screw.

It is pretty much now the only thing I can think of.....this contraction of coolant as it cools is drawing air in somewhere creating an air pocket!
 
Ant here is a problem ive got the large top hose that connects to the radiator whilst driving is fine no leak but when the engine is switched off and it cools down there is a minor drip. to combat this i have applied some instant gasket before i put the pipe on. i put it down to the after market radiator that i had replaced may be slightly different pattern to original. i note that you changed your rad so when its cool give the top hose a wiggle it could be a source for air ingress? failing that my cousin (a mechanic) told me there is equipment that can pressurize the coolant system when cold to find leaks. just an option?
 
Saint.V8 said:
Hi John,

Thanks for your thoughts....

There was no over pressure during the sniff test, the stat is still out and has continued to over pressure even with that out.

Even on Petrol she still gets a hammering now and then with high revs and fast running.

No pressure from the oil cap and no 'mayonnaise' either.

Curiously, and this is where I am heading at the moment is during running and immediately afterwards, the coolant is at normal level, this is proved by removing the cap after a long run and there is no excessive hiss nor is the coolant level over flowing the tank.

BUT, This is what I think may be happening, as she cools down the contraction of the coolant is drawing air into the system from a split hose, crack coolant/heater manifold on the back of the engine......then when I run her again, this creates an air pocket which works its way up to the top of the rad and sits there. this causes the level in the expansion tank to rise and over flow blowing coolant out when the air pocket gets hot and expands.

This I can assume, explains the reason why when you open the bleed screw the level in the tank drops as the air is expelled through the bleed screw.

It is pretty much now the only thing I can think of.....this contraction of coolant as it cools is drawing air in somewhere creating an air pocket!
Click to expand...
Sounds like a good theory Ant:)
 
A video paints a thousand words.

https://www.youtube.com/watch?v=kqguce0BHso

Car is cold, been sat at work for 6 hours after a 26 mile run to work.

As can be seen as soon as the tank is opened, the water forces itself out....open the bleed screw and the level drops.

When the car is hot after the same run, I can open the tank cap (with care!!) and the water level is exactly where it should be....

I can only assume as the coolant contracts it is drawing in air!
 
Last edited:
ant after the fluid has come out the level seems correct if you do not add any fluid does it do it again?. in mine i only fill until the indicator just pops up which leaves quite a gap for expansion
 
johnsteele said:
ant after the fluid has come out the level seems correct if you do not add any fluid does it do it again?. in mine i only fill until the indicator just pops up which leaves quite a gap for expansion
Click to expand...

After the fluid comes out and I open the bleed screw the level returns to normal, i do not top up from there.....

It does do it from there too, I am aware of the correct level position and also the correct bleed method, i have emptied and refilled the cooling system many times on this car and never had issues in the over two years i have had her...Just at the moment, something is amiss somewhere.

I do leave adequate expansion room in the tank, and fill to the correct level, i do not overfill.
 
long shot again ant but did you use any sealant recently/lately even 12 months ago on any assembly parts. if so I recon you have a bit of excess poss even a slither thats dislodged & found its way where its basically pushing/pulling with water & blocking/unblocking quite poss in header tank itself
 
wil2813 said:
long shot again ant but did you use any sealant recently/lately even 12 months ago on any assembly parts. if so I recon you have a bit of excess poss even a slither thats dislodged & found its way where its basically pushing/pulling with water & blocking/unblocking quite poss in header tank itself
Click to expand...

Only when I did the water pump nearly 21 months ago, just a thin layer to keep the paper gasket in place during refit.

I am curious by Johnsteele's comment on the top hose....as the air pocket seems to be at the top of the rad, this is a good place to start looking.
 
Sounds like a whole lotta fun mate
Have you pressure tested or vacuum tested the system ?

Mine took ages to bleed after my water pump, left it running for about 1/2 hour with bleed screw out and just topping up the header tank until eventually I got hot air from the heater and no more bubbles
 
holidaychicken said:
Sounds like a whole lotta fun mate
Have you pressure tested or vacuum tested the system ?

Mine took ages to bleed after my water pump, left it running for about 1/2 hour with bleed screw out and just topping up the header tank until eventually I got hot air from the heater and no more bubbles
Click to expand...
They can be a pain to bleed that is for sure.

The system holds pressure but not tried a vacuum test...!!
 
Saint.V8 said:
When the car is hot after the same run, I can open the tank cap (with care!!) and the water level is exactly where it should be....

I can only assume as the coolant contracts it is drawing in air!
Click to expand...

Thats what made me think about a vacuum test that was all, think that would test it if its drawing in air anywhere
 
UPDATE:

OK, having thoughts and a fiddle with Photoshop to make the Cooling system diagram a tad more readable....

I attach this here....

65600d1415803239-now-curiouis-one-coolant-over-pressure-overheat-cool_full.jpg


Now as a recap, I am getting an airlock in the top of the Rad and the expansion tank is pressurised and when cold will spew coolant everywhere....the level in the tank is right up...open the bleed screw to release the trapped air in the top of the rad and the level in the tank drops back down!

Sooooo, me thinking, if the Gearbox oil cooler stat is failed closed, the return line from the tank is fitted to an outlet on this stat....if it is stuck closed, then when the coolant contracts and tries to drag the expanded coolant back out of the tank, it can't as it is blocked...and an air lock is created in the rad where the contracted coolant has left a void at the top....

I have ordered a replacement GB oil cooler stat to fit and see if this is the cause....

Any thoughts??
 

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Saint.V8 said:
UPDATE:

OK, having thoughts and a fiddle with Photoshop to make the Cooling system diagram a tad more readable....

I attach this here....

65600d1415803239-now-curiouis-one-coolant-over-pressure-overheat-cool_full.jpg


Now as a recap, I am getting an airlock in the top of the Rad and the expansion tank is pressurised and when cold will spew coolant everywhere....the level in the tank is right up...open the bleed screw to release the trapped air in the top of the rad and the level in the tank drops back down!

Sooooo, me thinking, if the Gearbox oil cooler stat is failed closed, the return line from the tank is fitted to an outlet on this stat....if it is stuck closed, then when the coolant contracts and tries to drag the expanded coolant back out of the tank, it can't as it is blocked...and an air lock is created in the rad where the contracted coolant has left a void at the top....

I have ordered a replacement GB oil cooler stat to fit and see if this is the cause....

Any thoughts??
Click to expand...
if im right with my knowledge when liquid is cold the molecules are tight together and when heated they force apart so that's where the extra volume of hot liquid comes from?????? the part im struggling to comprehend when you fill from cold there's no pressure (extra pressure) just as an example lets say 10 litres (cold volume) the the engine heats the water lets say 10.1 litres (hot volume)then as the engine cools it will return to 10 litres (cold volume) therefore wouldn't the air have to be drawn or pressurized in somehow?. the hot volume expansion should be taken by the rubber hoses so as it cools it should return to negative?. i see on the video there's a fair bit of pressure? (when returned to cold) just a thought the small hose from the radiator to the expansion tank. if disconnected from the rad can you blow through to the expansion tank when the bleed screw is done up? would i be right in thinking the air should rise to the highest point being the expansion tank not the rad?? if there was a clear passage?? probably useless thoughts ant but just trying to help
 
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