Good day all.

I have a 2005 s40 2.4i, the car runs just fine but I recently noticed a creamy or foam like substance in the expansion/coolant tank lid/cap. Looking at the coolant it seems to have an oily look to it but can’t really confirm this. I check the oil lid/cap and also dip stick and the oil seems fine no milky goop there.

What could possibly be the issue. Videos I’ve seen on Youtube suggest a failing head gasket and some suggest air is coming into the coolant tank and that I should replace the cap.
one video even suggested I add a head gasket sealer to the coolant as a quick fix.

also the check oil light flickers when stopped at a light or in bumper to bumper traffic.

 

Everything points to your oil and coolant systems being intermingled. Head gasket is a very likely source. Driving like it is now is only going to make it (much, much) worse. If the oil is compromised (or low) enough to cause low oil pressure at idle, your engine is going to be toast soon unless you get the problem fixed.

There are ways to determine where the leak is occurring, but I'm betting these are not in your wheelhouse. You're probably at the mercy of your best local mechanic.

 

the flickering oil light could also be pointing to an issue with the oil pump seals or its pick up or possibly an issue with the pressure sending unit. You'd need to drop the oil pan to see if there's any debris etc in there and filter the oil when draining to see if there's something in the bottom of the pan as well. Also some models/years have a recommended replacement part for the pick up - may be worth checking in with a dealer on that.

As to the head gasket concern, there are kits to test for HCs (ie exhaust gasses) in the coolant ($40ish at Autozone etc). Another test is to see if the system pressure is too high (ie combustion gasses again) - you can have a shop or find a tool to measure system pressure as well. Have you noticed if the hoses appear to swell or feel rock hard when running?

Its possible that you have a radiator problem and you are getting transmission fluid mixing with the coolant as on some models the tranny cooler is part of the radiator, so check to see if you have any froth on the transmission dipstick as well.

I agree with habby that its best to have a pro do some tests to be sure. In the mean time you can google on these topics to see more discussions.