C200cdi using coolant

[R W]

I have a Cclass 200cdi. My daily commute is 12mls each way. The car does not loose coolant. On a 30ml journey it requires coolant topping up. When it's needing topped up slacking the cap releases pressure and coolant fills the header tank. Had the system pressure tested, no visible leaks. Did a snif test showed nothing. A week later run up to temperature and did another sniffing test keeping engine at 2000rpm and it showed a change in test colour. I suspect head gasket starting to fail. But over 1000mls it's got no better or worse. Any advice would be appreciated.

 

[DSM10000]

Have you not already confirmed that the Head gasket is failing?

 

[Jobsworth]

EGR cooler a more common problem than head gasket on om651

 

[R W]

Jobsworth. I have been thinking the same over the past few days. tried by-passing it yesterday but didnt have joints the correct size to by-pass the cooler. Next chance will be Saturday.
If it was head gasket it would have surely got worse over the weeks of running it.
I will by-pass the cooler and take it for a run over the weekend