Hi Peter.N.

I had a similar problem with my C5 HDI 110 some years ago. The Citroen dealers denied any knowledge of head gasket problems with these engines, and were adamant that this was not a head gasket problem. My symptoms were similar to yours, loosing coolant with no trace. I established that the cooling system was becoming pressurised - after running at normal temperature - say an hour or more - allow the engine to cool down. My header tank still looked full until I removed the pressure cap . . . not easy, as the internal pressure was significant. I found the header tank was still pressurised the morning after a long run. Any good garage should be able to do a gas analysis in teh header tank to detect exhaust gasses. When the Citroen dealer removed the head they found the gasket blown between the water jacket and No. 4 cylinder, AND some corrosion to the head - would an earlier strip-down have been beneficial? They couldn't skim the head as the engine mountings are positioned in such a way as to limit the facility for skimming to max 5 thou - according to Citroen. Precious little change from £1K, so it was time to replace the C5, which I still miss . . .

Hopefully yours will be something minor . . .

Its the word in the middle that causes the problem!

Sorry to hear of your diagnosis, there's a lot of it about, wouldn't be to expensive to do it yourself though.

Hdi engines are much better than the old XUDs for gasket failure, I have a 406 with over 200k on it with the original gasket and my C5 has done nearly 150 but when I was looking to buy these cars I came across several with leaky head gaskets.