Coolant loss after thermostat opens

[Mischief]

After getting tired of topping up each week I decided to do a test, I topped up the coolant and ran the car, while the thermostat is closed coolant level stays as it was when topped up but as soon as it reaches temperature and the thermostat opens I get a lot of back pressure and the coolant just pushes itself out.

not sure where to look or what might need replacing so any help would be appreciated.

Cheers

EDIT: No oil/coolant mix BTW.

[T-Cut]

Your description suggests you did the test with the pressure cap off. Getting the system hot enough to open the stat will almost certainly result in ejection of some coolant through the filler neck. The cap must remain in place for the cooling system to work correctly. Basically, you have a leak somewhere. Diagnosis is a matter of step by step checking. How does the engine tickover when first started from cold?

TC

[Mischief]

Originally Posted by T-Cut

Your description suggests you did the test with the pressure cap off. Getting the system hot enough to open the stat will almost certainly result in ejection of some coolant through the filler neck. The cap must remain in place for the cooling system to work correctly. Basically, you have a leak somewhere. Diagnosis is a matter of step by step checking. How does the engine tickover when first started from cold?

TC

Ticks over normal as far as I can tell bit tappetey when cold but goes away when warm, it never over heats just loses some coolant (It only takes half or less of a 2ltr pop bottle every 2 weeks) I assume when it is at pressure it's never been a major issue as we don't drive that often during the week it's used mainly on weekends.

I just want to sort the coolant loss no matter how slight it is.

[T-Cut]

There are several weak spots in regard to coolant leaks. All need checking throroughly.

Every hose, hose connector and clip.
The pressure cap seals.
The inlet manifold gasket. Typically causes a lumpy cold tickover due to water getting into cylinders 1 and 4. Unusually steamy exhaust.
The water pump. Look for drips behind the crankshaft pulley.
The thermostat housing seal.

You should confirm the radiator fan works properly. Run the Demist test.
Check the typical running temperature using Diagnostic Mode. Should be around 90-95C.

TC

[Mischief]

Originally Posted by T-Cut

There are several weak spots in regard to coolant leaks. All need checking throroughly.

Every hose, hose connector and clip.
The pressure cap seals.
The inlet manifold gasket. Typically causes a lumpy cold tickover due to water getting into cylinders 1 and 4. Unusually steamy exhaust.
The water pump. Look for drips behind the crankshaft pulley.
The thermostat housing seal.

You should confirm the radiator fan works properly. Run the Demist test.
Check the typical running temperature using Diagnostic Mode. Should be around 90-95C.

TC

Radiator fan works, temp is as it should be no overheating at all just the slight coolant loss. I have been looking over all the pipes and joints after a run and simply can't see any drips or leaks which is why I am at a loss, It's not even a big problem just a pain having to check and top up every 2 weeks or so.

[The Rovering Member]

I also get coolant loss but get lumpy cold tickover syndrome so have a new inlet manifold gasket to fit.

[murphyv310]

Hi.
We all know that the cooling system is weak point on these cars. Personally I check my coolant at least once a week and before a long run. I wonder if the OP may just be overfilling the expansion tank and the "leak" is just the coolant level stabilising?

[Mischief]

Originally Posted by murphyv310

Hi.
We all know that the cooling system is weak point on these cars. Personally I check my coolant at least once a week and before a long run. I wonder if the OP may just be overfilling the expansion tank and the "leak" is just the coolant level stabilising?

I know exactly where to fill it to because I can read and have been topping the coolant up since 2011.

[T-Cut]

Internal leaks are a possibility. I had one with no external signs whatsoever.

TC

[Mischief]

Originally Posted by T-Cut

Internal leaks are a possibility. I had one with no external signs whatsoever.

TC

I have no oil/coolant mix though and no signs of issues when I had the service on the last mot a few months ago