2013 XC60 T6 (non turbo)
Preface: We presently live in Doha, Qatar and the temps have been 110*F lately.

Problem: Yesterday my wife was driving home from work in middle of day at height of heat. Probably 10 miles. It stalled on her when coming to a stop at lights a few times. Push the button and it starts right up and goes but did it a couple more times. I took out today and drove same amount and did on me once. But again pushed the button and it started right up. Another time I pulled over and the rpms went to 0 but then popped back up to idle rpms.
A mechanic who I'm not sure I trust stopped by and said either the fan wasn't working or it was the head gasket. The fan works fine. I did replace the control module about a year ago but have had no issues. I had a car once with head gasket issue and there is no sign of head gasket issue here. No white smoke, no "milkshake" in the crankcase, not losing oil or coolant at all. Not sure why he was saying that and didn't sound correct. and he was making the diagnoses without even testing the usual signs. But I'm no expert mechanic either. My thoughts were it's just vapor lock due to the heat. Any ideas? The problem here is they just throw a "fix" out there, then the next, etc until they finally solve the problem and head gasket just doesn't sound right.