Oil in Coolant?

[MattBLancs]

could one of the causes be the oil cooler?

My understanding is the oil "cooler" (which is an oil-coolant heat exchanger) can fail but tends to be very significant volumes of oil into the coolant (and header tank full of black muck rather than your frothy cappuccino )

Potential you've only "early stages" of cooler failure but otherwise head gasket is possible.

How is coolant temperature behaving (not running hot?) no experience of 1.6 HDi in a C5 but other applications it has normal running temperature of 90° C on the gauge.
How is engine performance - hard to say if you've not had it long?
How are coolant hoses? (Not rock hard as under significant pressure?)

Is is pushing any coolant out of the expansion tank?

Perhaps ignore me as seems I'd missed 2 extra pages of responses!

[PaulC5]

Just thinking this out, when the expansion tank cap is off and the engine is cold, putting the cap on locks in the air and coolant. As the engine heats up the coolant and air expand and the pressure goes up, also the coolant vapour pressure increases. Then when it cools down the pressure should then drop back down as the air and coolant contract. Only way the pressure can remain high once cooled down is if more gas has gone in which goes not condense and that can probably only come from a leaking head gasket. Hope I am wrong but it could be the head gasket is leaking.

[Hannya92]

Hopefully you wrong but I agree... The only thing that would led me to thinks it's not head gasket is the fact that the car performa well and there's no errors, also fuel consumptions are perfect. I had cars with faulty head gaskets and you could definitely see something weird on the performance of the car...this is not the case.

[myglaren]

Try an exhaust sniffer to see if the coolant is contaminated with exhaust fumes. Could be a very small leak. Best to know early as it will only get worse.

[MattBLancs]

Just before that, has the original fault: yucky mayo in the coolant not returned since the cooler replaced and many miles covered?

(Just catching up on the other responses and don't see any further mentions of the header tank mess since)

If coolant remains ok, temperature is ok (and 80°C is ok, as you say 83°C thermostat), engine performance seems ok- then I'd be tempted to use it for a bit and see how it goes, but with regular checks:

If you see any overheating,
Or it's pushing coolant out,
Or the mayo returns,

Then something is amiss,

[PaulC5]

Yesterday on tv there was a Flipping Bangers episode where they had an old Renault 5. They had been told it overheats but they could not find anything wrong, the car ran normally and they did not get it to overheat. Tests included driving it, flushing the cooling system, making sure the water pump was working, put the engine fan switch in hot water and the fan ran, tested the cylinder compressions. As a last resort they used an exhaust fumes test on the expansion tank and it changed colour from blue to green showing the presence of carbon monoxide and hence the head gasket had a leak. On taking the head off they found some slight cracks on the head at the gasket surface and it was possible to skim it to remove them. Their test was only about £20.

[Paul-R]

That second series was made in 2018 so prices will have gone up a bit.

It's a good series showing the warts and all. Although they do gloss over an awful lot. I watched an episode last night where they did up Triumph Herald and it was only in the last few minutes when they rolled it out of the workshop that I noticed the four new tyres. Not mentioned at all and not included in the costing.

[Paul-R]

That second series was made in 2018 so prices will have gone up a bit.

They had a pixel display repair done to the instrument binnacle by Cartronix and it cost them £100. Latest price is now £120. About what I would expect I suppose.

[Hannya92]

Left the car for 3 days without running and when e removed the cap (slowly) the coolant came out bursting again....wondering if this if the pressure release hose should be connected to the highlighted red part instead of the orange

[moizeau]

That is not happy coolant, deffo oil in there. I did a test on a friends car with a suspect HG failure using a swimming pool PH tester. At the very least it's another drain, flush and refill before the place of contamination can be found. I wouldn't bother using antifreeze, just water as it's for testing purposes.

[Mihael_M]

As you can see on the other engine, the connection is the same as yours.

[Hannya92]

Thanks for confirming, FYI the coolant in that picture was before I changed the oil cooler, now it has shown any signed of contamination

[Mihael_M]

Well, that's fine with the coolant then.
And what you're noticing is that there's still pressure in the system after 3 days, maybe it's nothing controversial. Maybe if you can get another cap for the coolant reservoir. That cap should release excess fluid and pressure. It's not an ordinary cap that just closes.

[Hannya92]

just want to close this post to say the initial issue was a bad oil cooler followed by a stuck open thermostat...

[ekjdm14]

Glad to hear it, I've only just caught up with the thread again but thought I'd mention I've had a few cars where they held pressure after sitting & never had a problem with them. Only time I'd be worried is if the antifreeze concentration was suspect & the pressure (possibly, in theory) caused by some kind of off-gassing/byproduct of corrosion but doubt this is the case as it's fresh coolant.