I checked the dipstick and there was no oil showing on the dipstick, which means that the engine lost at least a quart of oil into the coolant in a matter of seconds (it was full before I started driving). Needless to say I got the car towed, and had her taken to a local indie Volvo shop (don't have time to fix myself right now). I need a bit of help figuring out what's going on. My thoughts are this was either a head gasket failure or a catastrophic oil cooler failure, one that caused enough oil loss in seconds to give me low oil pressure--although I've searched the forums and haven't found an account of this exact thing happening. My gut is telling me that the oil cooler makes more sense--the car didn't overheat, and was running smoothly with no CEL when this all happened. Doesn't fit the picture of a blown head gasket. To add complexity though, a mechanic I took the car to for something else 10 years ago said that a coolant test strip showed combustion products in the coolant (indicating a head gasket leak). Although I trust his word I wasn't sure that the test was accurate at the time since the car had no such issues, and the car has run great for 25,000 miles since then with no issues, no CEL, no coolant loss, no water in oil, and no overheating problems since then until this week—I’d basically forgotten about it and seemingly with no issue.
Now, with my car in the shop for the current oil loss problem, my mechanic calls me today and says that it's "definitely the headgasket" because there was "pressure in the coolant circuit." I believe he's referring to the oil/coolant that sprayed out, and I don't believe he's done any actual tests yet. To me this pressure could logically be caused by a failed oil cooler leaking oil pressure into the coolant circuit. When I asked him about the oil cooler he said it might ALSO be an oil cooler failure on top of a head gasket failure.
I'm skeptical that the headgasket and oil cooler would fail at the exact same time, and that with a major headgasket failure the car would still be running fine with no CEL. I’m skeptical there is anything wrong with the head gasket, or even if there is, that it caused this recent catastrophic loss of oil pressure and oil in the coolant. Would really appreciate any input on what could be most likely, and also if there are any tests (leakdown testing, pressure test the radiator?) that I should have my shop do that would tell us if this is really a blown head gasket or if it’s the oil cooler. The reason this is so important to sus out is if it's just the oil cooler I'll have it fixed for about a grand, but if it's the head gasket I probably won't be fixing the car :'(
