Citroen C5 2.7Hdi - Coolant/Gasket Problem

[rav]

Hi everyone, I’d like to ask for your opinions on an issue I’m having.

After driving the car a bit harder and then stopping, I noticed coolant coming out of the expansion tank and some smoke/steam from that area.
I let the engine cool down, topped up the coolant and tried to bleed the system. At first everything seemed fine.
However, once the engine reached operating temperature (probably when the thermostat opened), the coolant in the expansion tank started behaving like it was boiling and was being pushed out violently.
Even with the cap loosened, the coolant was violently splashing out of the tank, almost like a small fountain.

My initial suspicion is a head gasket issue, but I’d like to get some opinions before jumping to conclusions.

[PaulC5]

Could be the head gasket, try a combustion leak tester, they do not cost much.

[wurlycorner]

That does indeed sound like head gasket unfortunately - surprising, as that's not a common fault on those.
Should be easy to confirm though, as Paul says.

[rav]

I’ll do this test over the weekend, since that’s when the car will make it to the garage.

The only other thing I’m wondering about is whether it could be one of the EGR coolers. In that case, the test would also show contamination, and replacing the EGR cooler would be a much better outcome than dealing with a head gasket or cylinder head.

[PaulC5]

I would think the exhaust gas pressure in the egr is less than that of the coolant and far lower than in a cylinder. If so then it unlikely exhaust fumes would end up in the coolant tank. Others may want to comment in case I am wrong.

[wurlycorner]

I would tend to agree with Paul - if the cooling circuit in the EGR was leaking into the exhaust circuit of the EGR, then I'd expect coolant to be drawn into the cylinder (as the EGR feeds the intake side of the engine).
Removing the air inlet pipe between the EGR and intake manifold should confirm - would reveal evidence of coolant in the pipe (and would be cleaner than expected, not furred up with carbon!)

[rav]

The car was delivered, and at the workshop they topped up the coolant and bled the system. And… absolutely nothing happened. After that, a CO₂ test of the cooling system was performed, which also showed no issues. I drove about 20 km and nothing at all is happening. I have a 120 km trip tomorrow and honestly, I don’t know whether I should go or not.

[Paul-R]

When you say nothing, do you mean nothing untoward? I.E. it appears to be fine now?

[rav]

Yes, it’s working completely normally. No errors in the control modules and no physical issues at all.

I’m wondering if the transmission might have overheated the fluid. I was driving in sport mode around the city, and I’m thinking the gearbox could have gotten too hot.

Or maybe the thermostat got stuck, and after the car sat for a while, it freed up again.

And just to say upfront—I know that wasn’t the smartest thing to do.

[rav]

On another look it seems like plastic part is leaking coolant.
Catalogue number: 1336.Y2
I’m just stumped how to get to it.

[MGmike]

On another look it seems like plastic part is leaking coolant.
Catalogue number: 1336.Y2
I’m just stumped how to get to it.

I find the easiest way is to remove the bumper and cooling pack!
It might seem overkill but the alternative is to go in from the bottom. You'll need to remove the AC compressor and the alternator but even then, there's not a lot of room to get the hose clamps off.