Oil in header tank ? oil cooler or head gasket?

[alf1956]

I have a Merc Clk 270cdi 2005 reg which has been parked up for a 12 month period as it has a gearbox fault which i am eventually going to get fixed & i occasionally run it around the estate where i live & start it up to keep the battery charged up & today i started the car up & let it tick over for around 20 minutes & i noticed a small leak around the top radiator hose which has been like that for many months but not a massive leak more of a drip so i took the hose off & cleaned the metal part up & re-fitted it, i then topped up the water & ran the car for a while whilst stationary on the drive & topped the water up as i had lost some with taking the top radiator hose off & then i noticed oil in the water in the header tank but what is puzzling me is that water that came out of the radiator was pure water with no oil in it at all??? Head gasket or oil cooler? I fitted a new radiator on the car 12 months ago & i have not done 1,000 miles since the radiator was fitted.

 

[Tezz]

I would say check cooler, when its cold have a look around and see if you can see any water or damp area, will just be a tiny amount only when cold as it seals when hot.

When I looked after a fleet of 150, ever single one suffered the same issue, it took years for the maker to modified the cooler

what was happening was the ally cooler and cast block were separated by a rubber seal, when cold they all contracted at different rates, first sign was a small damp patch or drip of water, then after a few week it got worst till the seal between oil and water gave way and oil made is way to header tank, yet when hot there were no signs and all tests showed it air tight under extreme pressure, which is why took years to get part modified

Fixing issue was not problem, getting rid of gunk was

 

[alf1956]

Anybody got any info on what kind of job it is to change the oil cooler please?