07 Yaris S Blown Head Gasket?

[ylerT]

New to the forums and trying to get some info about an issue we're having. Quick rundown...my wife's 2007 Yaris S just hit 80k miles, started overheating and we were told by a mechanic that it has a blown head gasket.

About 3 years ago, she accidentally put a couple gallons of diesel in the car (long story, don't ask haha). We ended up having the whole car flushed, catalytic converter and sensors/misc parts replaced. Since then it has been running perfectly fine, no issues with anything.

Well last weekend we took a trip to Anaheim and on the way started seeing the coolant light blink. Turning off the AC would make it go away almost immediately if we weren't on a hill. Basically after getting further into Cali with the cooler weather it was fine. On the way back a completely different story. It was blinking constantly, a few times it went solid and we actually pulled over to let the car cool down before continuing home.

All this week, my wife has seen the light go solid after less than 10 miles on the freeway. If she is driving short distances on surface streets, it's rare for the light to even blink unless the AC is full blast. We took it down to a mechanics, he says everything seems fine (radiator, thermostat, etc) and that he had a Civic that did the exact same thing...head gaskets blown.

Basically I'm just looking to see if anyone has seen something like this before? I'm not very knowledgeable on cars but a blown head gasket at 80k seems strange. Could it have been affected by the diesel fuel years ago? Also, what should I be looking to pay for a head gasket replacement if that is what it needs?

Thanks everyone!