I’m at a loss as to who to believe now. Recently, my 2013 Chevy Sonic (approximately 140,000 miles on the car, recently new water pump and thermostat and housing) began beeping with an oil pressure light on constantly. I took it to my regular mechanic, where the oil filter and oil pressure sensor were both replaced, twice, to no avail. Then, I took the car to a dealer. There, they diagnosed a coolant leak originating in the thermostat and housing that had gotten coolant into the wiring and the ECM (electronic control module). They quoted me over 2,000 dollars to replace the thermostat and housing, replace the engine wire harness (which they told me was completely fine, just potentially wet), and to replace the ECM. I did not let them do these things.
I took it back to my regular mechanic to ask them to check the thermostat and housing for a leak and clean up the wire harness if possible. They then told me that the thermostat and housing looks completely fine, that the wire harness replacement is unnecessary, and that they thought what the problem actually was. A blown head gasket, sending oil up into the coolant.
Now, these things do not seem related to me. Just looking for some thoughts from the community, since I have no idea who to believe at this point. Thanks!