pressure in cooling system

olistr · Jun 14, 2023

Hi,
I have a TD5 from 2002, all stock, it has 320k and when I am driving a while, pressure is building up in the cooling system.
When I stop the car, the cooling level is far down, when I open it, it bubbles a little and air comes out and then the level goes back to normal.
I have been in the garage, they are saying there are no signs of exhausts, in the cooling, so it is somewhere else.
It is not heating up, no loss of coolant.
Any Idea where this could come from? The garage couldn't find anything and suspects the motor block potentially being cracked.
Any suggestions are welcome.
Olivier

tottot · Jun 14, 2023

It is normal for system to pressure up some when running, this is done so coolant has a higher boiling point than if at normal atmospheric pressure. Opening the expansion tank when hot can be dodgy, [ and very dangerous if head gasket gone or other damage results in very high pressure in tank ] as some blow out can happen as pressure drops due to bubbles forming as you have observed.
As you are not losing coolant and temp gauge is good and have had exhaust fume check I recon its fine, just keep checking the usuals.

Turboman · Jun 14, 2023

olistr said:
Hi,
I have a TD5 from 2002, all stock, it has 320k and when I am driving a while, pressure is building up in the cooling system.
When I stop the car, the cooling level is far down, when I open it, it bubbles a little and air comes out and then the level goes back to normal.
I have been in the garage, they are saying there are no signs of exhausts, in the cooling, so it is somewhere else.
It is not heating up, no loss of coolant.
Any Idea where this could come from? The garage couldn't find anything and suspects the motor block potentially being cracked.
Any suggestions are welcome.
Olivier

Doesn't really sound like you have a problem.
The plastic expansion tanks on those don't last for ever, and can split on the seam, and allow a bit of leakage, but I don't see how that could ever draw air in, as there should never be negative pressure on the system.

If you do have a problem, it will probably get worse over time, making it easier to diagnose, so I would just carry on a usual.

olistr · Jun 14, 2023

Hi,
thx for the quick reply.
It only started doing it so I was a bit surprised.
I will try replacing the cap first, maybe just defective walves

johnlad · Jun 14, 2023

There’s a valve in the expansion tank cap which are known to fail on td5, a new cap ain’t expensive so worth changing it.

pressure in cooling system

olistr

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tottot

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Turboman

Mab An Gov

olistr

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johnlad

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