2008 A6 4.2 80k

Oil light came on, as it's done before many times... Every A6 I've owned has burned oil. But when I opened the hood to add a quart, I noticed the top of the coolant reservoir has become dark. I remove the screw cap to the reservoir and there's oil right on top sitting there. It hasn't mixed in the pan (or mixed in the coolant reservoir), and when I pull the coolant hose that leads from the throttle body to the back of the reservoir it pumps mostly coolant but every few sec or if I rev higher, some oil starts to flow. I cleaned out the oil and refilled with coolant. I let idle and it took about 2 hours to start to pump oil into the reservoir again.

I'm thinking oil cooler. Advice appreciated. ANyone seen such a thing?

 

First thing, don't wait till the "oil light" comes on to check the oil. Second, is it oil or is it transmission fluid getting into the coolant? If it's transmission fluid, the cooler in the radiator is leaking. This is NOT good for the transmission. I'd drain the transmission fluid and check for coolant in that first. If no coolant is found, you can breathe easy that your transmission is not damaged.

If it's engine oil, there's definitely a leak somewhere. Most likely a head gasket as I don't think oil is circulated into any of the throttlebody elements.