Help please - Pressure in coolant when cold

Thanks for all the thoughts and comments, I'll monitor the level as if it goes down with the cap in place for a few days driving then the engines eating it somewhere.

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THe above diagram is awesome, Ill check for oil out the block to heaad join, no water in the oil ive checked that and I get a pass when testing thte coolant for hydrocarbons.

I have some blue smoke out the back sometimes, but this I think is turbo letting some oil out the into the exhaust. That said I still need to replace the egr to be sure.

I popped the filler cap in the rocker cover while running warm and revved it, and still got blue smoke puffs - so I dont think its crank case pressure giving smoke.

Anyway back the coolant, I will come back with findings of any water consumption Friday.....
 

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Ive checked the gasket using a tester and its saying its okay? Did a fair few tests on it. Maybe its a slight head gasket split, small for now! So to fix would need a head skim and new gaskets?
The manual says that a TDi head should not be skimmed. Head gaskets come in more than on thickness, the correct one must be used.
 
The manual says that a TDi head should not be skimmed. Head gaskets come in more than on thickness, the correct one must be used.
Hi Phil, good advice I recall this comment from perhaps your thread recently taking head off. This is due to powerful compression alterations?
I've been talking to my local and he's on board with gaskets, we've talked about using larger gaskets already. Just awaiting quote for the work, fingers crossed its worth saving!
Fairly convinced if the headgasket gets solved I'm left with good 140k tdi. The gearbox is great and it's driving really well.
I'll have turbo assessed when off.
Let's hope it returns to me and doesn't end up another dead tdi. I think its worth saving given its milage condition drive and history.
 
For many years, I never worried too much about the coolant level. Then I noticed a small puddle or two of water under the car, if it was left standing for more than two or three days. I immediately checked the water tank and to my surprise the level was half a centimeter below the minimum and never any marks on the dashboard! . On closer inspection, I noticed micro-traces of coolant on some hose/sleeve seals. Where I was able to access, but with tremendous difficulty, I also replaced and added hose clamps. The situation has improved, but only if, after each trip, I gently open the cap to let the pressure drop, then the level immediately rises by almost 1 cm. I close everything and when the engine is very cold the level is almost back to the same as at the start, less about 1 millimeter, after 100/120 km covered. I'll probably have to find a permanent solution
 
Interested to read this thread as I have the same phenomenon occurring with my Lotus Exige which running a K series does have a certain reputation for HG. That said the car was running fine but coolant tank was pressurising and level dropped sightly. Same thing, release cap even when cold and a slight hiss and the level returns to normal. Still to determine the issue though new header tank is to be fitted next on advice these can fail and weep. Having noticed some coolant underneath mine this seems a sensible precaution to swap out for a new one. Ongoing, hopefully not HG, will see though.
 
Interested to read this thread as I have the same phenomenon occurring with my Lotus Exige which running a K series does have a certain reputation for HG. That said the car was running fine but coolant tank was pressurising and level dropped sightly. Same thing, release cap even when cold and a slight hiss and the level returns to normal. Still to determine the issue though new header tank is to be fitted next on advice these can fail and weep. Having noticed some coolant underneath mine this seems a sensible precaution to swap out for a new one. Ongoing, hopefully not HG, will see though.
Oh yes legendary k series HG, dad had a nice 420 GSI ROVER, lovely drive but never lasted. I may try a new header tank but can't find one!
 
HI,

AMF tdi75 no mods all stock, no AC but with webasto.

Coolant level was checked, its at low line. Drove to work all good. Went out just now engine cold, coolant level dropped about 2cm form low line. I undid the cap and ''POP'' with some splurge out the vent of the expansion header tank.
Level back up to near min line again.

One thing I did do is change the coolant cap for 'similar' one I have in the garage, this was because I could hear it letting some air out, or sucking in, one of other when hot.

Engine sounds sweet, runs smooth and heats up normal time and doesnt overheat. Is the header cap the type that lets pressure in and out?

Other than popping old one back on tonight, any ideas good people?
The way I understand the expansion tank works is the air above the coolant acts as a spring. The coolant expands the air compresses. The coolant cools and goes back to its normal level. If the cooling system overheats or is over filled the cap relieves the pressure to protect the system components. If the system leaks when in use the cap will allow air in to compensate for the lost liquid.
The biggest worry is that you have a blown head gasket but you have tested for that.
It has been suggested there could be air in the system but, without checking, I believe you are confident there are no air locks.
I think as the level returns to normal when the cap is removed and you have tested for combustion gasses in the coolant I would not worry and just drive the car.

A thought though, do your pipes expand significantly when hot / warming up? Perhaps they expand more than the coolant allowing.the level in the tank to drop and air is taken in. At full temperature the system is pressurised below the relief pressure so some pressure remains due to the excess air as the system cools. That is the pressure you relieve when you take the cap off. Air is not in but it is getting in. A thought I came up with while reading through the thread.
 
Good stuff Phil, I think I'm going to flush the system nd start again as a next step, as I added some g12+ mannol coolant and now I can see some slime stuff so maybe the coolant in there isn't right? It was pink.
So to be sure I'm going to flush it out and put g12+ in, this should also clear and trapped air.
 
Good stuff Phil, I think I'm going to flush the system nd start again as a next step, as I added some g12+ mannol coolant and now I can see some slime stuff so maybe the coolant in there isn't right? It was pink.
So to be sure I'm going to flush it out and put g12+ in, this should also clear and trapped air.
I think I have G12++ in. Don't forget to flush the heater matrix too.

I'm taking Little Dog on a salad hunt shortly, will note what happens to the coolant levels and advise.
 
Firstly I can't see how coolant gets out or air gets in but I believe they both do:

IMG_0619.jpg


The car has been stood for a couple of weeks, there was no pressure in the cooling system. The coolant level is slightly above max:

IMG_0620.jpg


6.4 miles to the supermarket on fast A roads and the gauge has only reached 70:

IMG_0621.jpg


10 minutes later, tomatoes and cucumber bought we are back down to 60.

IMG_0622.jpg


I decide to go the long way home, steep hill climb plus a bit of motorway:

IMG_0623.jpg


That's better, the car made 90 at 9 miles but the motorway will have made sure the thermostat is open. Coolant level has increased slightly with the engine running:

IMG_0624.jpg


I turned the engine off and the level remained the same. I expect the level will return to the first mark when cold and there will be no pressure.

Conclusion @CrispyEdd , you have a fault.

Edit, 24 hours later the coolant is back at the initial cold level and there is no pressure in the system.
 
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The caps do let air in and coolant out. This is a cap from a MK2 Golf, pressure coolant relief is on the left. The disc on the right is a lightly sprung non return valve that will let air in.

IMG_0625.jpg
 
Firstly I can't see how coolant gets out or air gets in but I believe they both do:

View attachment 104936

The car has been stood for a couple of weeks, there was no pressure in the cooling system. The coolant level is slightly above max:

View attachment 104937

6.4 miles to the supermarket on fast A roads and the gauge has only reached 70:

View attachment 104938

10 minutes later, tomatoes and cucumber bought we are back down to 60.

View attachment 104939

I decide to go the long way home, steep hill climb plus a bit of motorway:

View attachment 104940

That's better, the car made 90 at 9 miles but the motorway will have made sure the thermostat is open. Coolant level has increased slightly with the engine running:

View attachment 104941

I turned the engine off and the level remained the same. I expect the level will return to the first mark when cold and there will be no pressure.

Conclusion @CrispyEdd , you have a fault.
Wow so good of you to do a test thank you, yes mines the opposite isnt it goes down with a pop when cap comes off! Your experience there is what I would expect. Thanks!
 
I think I have G12++ in. Don't forget to flush the heater matrix too.

I'm taking Little Dog on a salad hunt shortly, will note what happens to the coolant levels and advise.
How do i flush the heater matrix, by having the interior dial on max heat?
 
How do i flush the heater matrix, by having the interior dial on max heat?
Disconnect both pipes at the engine. Put a hose on on and flush until clear. You will have a small amount of tap water in there as I did. I additionally blew air through and and got a bit more out. I figured a bit of tap water was better than a bit of the wrong coolant.
 
Disconnect both pipes at the engine. Put a hose on on and flush until clear. You will have a small amount of tap water in there as I did. I additionally blew air through and and got a bit more out. I figured a bit of tap water was better than a bit of the wrong coolant.
These into the bulkhead you mean? but where they connect nito the engine bay somehwere, trace them back?

1677159595926.png
 
These into the bulkhead you mean? but where they connect nito the engine bay somehwere, trace them back?

View attachment 104945
Those are the two, I think they connect under the tandem pump. Mine are new so they must have had diesel contamination from the original pump.
I flushed the heater, engine and radiator separately. Probably overkill but my new antifreeze was not compatible with my old antifreeze.
 
The way I understand the expansion tank works is the air above the coolant acts as a spring. The coolant expands the air compresses. The coolant cools and goes back to its normal level. If the cooling system overheats or is over filled the cap relieves the pressure to protect the system components. If the system leaks when in use the cap will allow air in to compensate for the lost liquid.
The biggest worry is that you have a blown head gasket but you have tested for that.
It has been suggested there could be air in the system but, without checking, I believe you are confident there are no air locks.
I think as the level returns to normal when the cap is removed and you have tested for combustion gasses in the coolant I would not worry and just drive the car.

A thought though, do your pipes expand significantly when hot / warming up? Perhaps they expand more than the coolant allowing.the level in the tank to drop and air is taken in. At full temperature the system is pressurised below the relief pressure so some pressure remains due to the excess air as the system cools. That is the pressure you relieve when you take the cap off. Air is not in but it is getting in. A thought I came up with while reading through the thread.
I drive the car 50 miles today there was coolant on the header tank, the little vent hole was wet. The coolant level was low but hast gone down. I haven't opened the cap as I want to test it see if it goes down further. Hoses are not squashed under vacuum. The top hoses felt fairly firm though while hot.
I took a really good luck at the hoses under the tandem pump and one was ballooning quite a lot, its been cleaned off. I'll see what it's like when cold.
I'm checking for pressurisation.
 
The firmness I did experience but the balooning never. Also it is a different engine on ours so the temperatures might be different. Maybe you can also do the vcds test that I did with the measuring blocks and see if it makes any sense.

Have you tried the sniff tester after the car has sufficiently warmed up?
 
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