Cracked head (gasket?); need advice on what to do next

[Scoobey]

Hi, helpful folks! My 2009 C70 (124,000 mi.) has been running a little rough for the past week, then the other night we had the following sequence of events:

- No heat from heater. (My brain: ok, need a new heater valve, nbd.) Then:
- Oil light comes on. (A grocery store's right there, so I pull in, buy a quart, put it in.) Oil light goes off.
- A couple miles later, oil light and then check engine light come on. I pull oil cap; visible vapor comes out (very hot oil?), but temp gauge shows dead center.
- Half mile more to destination, park car, Lyft home, have it towed the next day.

Mechanic just called, said it was completely out of coolant and that an air bubble around the thermostat might be responsible for there being no indication of high temp. Said it's probably a cracked head gasket that allowed coolant into the cylinders until it was all gone, and that replacing the gasket, machining the current head, replacing valves, etc. will be $3,500-$4k (and a few hundred more if a new used head is needed). Codes he pulled included ECM3100, 3110, 3120 (specific cylinder misfires), ECM3410, 341c, 341d, and 2B00 (bad thermostat sensor -- ???), and 304c (knock sensor).

Questions:
- Does my mechanic's explanation sound right? Do head gaskets just fail like that in the absence of some other problem? I'm more used to high temp CAUSING a cracked head etc.
- Would you recommend replacing the gasket etc., or would it be better to find a low-mileage used engine, or even a remanufactured engine?
- In short, what's your advice for restoring this car to reliable condition without breaking the bank, and making sure it doesn't happen again?

Thanks!!

[Clemens]

If you can source a known good engine a swap might be the cheapest solution.
And yes, these sound like plausible head gasket failure symptons.

[June]

Sounds like you drove it for several miles with no coolant. Therefore I would never try to fix the gasket. I would buy a used engine complete with turbo. Oil light means that turbo and engine ran without adequate oil while no coolant = bad news for turbo as well as engine. Remember that turbo was spinning faster than the engine without any protection. So +1 for used engine. June