Coolant pressure testing question


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Coolant system pressure testing question

I did a pressure test on my radiator for my 03 leSabre. It held pressure but slowly dropped. In 8-10 minutes it had lost slightly more than a pound.

Is this normal? Should it hold without any loss? I found one place on the web that said a slow loss was not a concern.

The upper and lower gaskets were replaced a year ago.
Last edited:


Full Member
Buick Ownership
Buick lesabre
there should not be any loss. it should maintain a constant 15 psi. it will relieve pressure only when above 15 psi, back too 15 psi.


Full Member
Vancouver BC
Buick Ownership
1997 Buick LeSabre
One pound in 15 minutes is a fair bit. However, if the engine was still warm the contracting fluid could cause a pressure drop without a leak. Make sure you do your pressure test on a stone cold engine.

Also, if you have any air in the system, if the air dissolves into the water under pressure, you will see an apparent pressure drop.

You could leave the tester on all night then check the pressure in the morning. Then check around for any external leaks. The leak could be at the radiator cap neck if the pressure tester doesn't seat properly. If you really do have a leak, when you remove the pressure tester you will have an air space at the top of the radiator. If you don't have any air in the top of the radiator, it is probably just loss through the tester attachment.

However, an 03 isn't too young to have failing LIM gaskets. If they're the old plastic style I'd replace them for insurance! I did my wife's car which showed no leaks with my rad tester, but I found the gaskets were about to go.
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