Coolant loss mystery

[JohnCa]

Hi everyone,

I have a Citroen C4(2011., 70kW, petrol engine) which drives me crazy. The issue is coolant loss through filler cap. The most frustrating thing is that loss is not constant and it is happening once in a month or two. Also noticed the problem will appear during city driving rather on highway. I drive 300 miles, everything is fine and sometimes just 10 miles and there is a coolant loss

We've tried a couple of things:

1)Head gasket replaced last year.
2) Replaced the expansion tank cap.
3) Replaced water pump
4) Pressure test on the coolant system overnight and everything good.
5) Test for exhaust gasses in the coolant - we couldn't find gasses.

I'd really appreciate if you could help me.

[petarc1971]

Since all checks have been done, it should not lose coolant. When the head gasket was changed, it may have been necessary to check that a stem did not have a crack.

[JohnCa]

Since all checks have been done, it should not lose coolant. When the head gasket was changed, it may have been necessary to check that a stem did not have a crack.

I mean, if it has to do with stem, how it's possible that I drive over 300 miles and coolant is not missing and tests( exhaust gasses and pressure) have passed?

[white exec]

Is the radiator cooling fan(s) operating correctly?
A long journey on open road will provide ram-effect cooling, where urban crawl will not, so relying on the fan.
Might be worth renewing the thermostat too.
Could the coolant be over-filled?
Is the pressure cap sealing properly?
Has all air been bled from the cooling system?

[petarc1971]

These could be the symptoms of a micro-crack of the stem, after city driving, the engine load is higher and it heats up faster, which is exactly why it passed all the tests. Of course it may not be that it's just a possibility, it could be a defect and the engine head. When the head gasket was changed, was a hydro test performed?

[JohnCa]

These could be the symptoms of a micro-crack of the stem, after city driving, the engine load is higher and it heats up faster, which is exactly why it passed all the tests. Of course it may not be that it's just a possibility, it could be a defect and the engine head. When the head gasket was changed, was a hydro test performed?

Hm, not sure I understand "hydro test. Is this same thing as pressure test on the coolant system? Also when you say stem, are you referring to the engine block? Sorry, my english is not very strong when it comes to car terminology.

It makes perfectly sense what you said about engine load after city driving, but what I really don't get why is this happening sometimes? If there is any crack in the engine, engine block etc, this problem should happen very frequently and especially during the summer and this problem should getting worse and worse(white milky oil, white smoke etc)

[petarc1971]

The hydro test is performed in a machine workshop after processing (straightening) the cylinder head. When I said stem I meant the part in the block where the piston enters. I'm using Google Translate so it might be confusing.

[petarc1971]

Cylinder head after straightening, no hydro test was done because there was no loss of coolant - removal is due to a broken glow plug.

[JohnCa]

According to you, how can I check if there is really micro-crack in the block?

[petarc1971]

It can be tested by applying air pressure to the cylinder and observing for bubbles in the coolant reservoir.