Head gasket blown after catalytic converter repair?

While it's always tempting to be suspicious, as a mechanic who is often on the other side of this... Sometimes coincidences are nothing more than coincidences. But, just in case, if you can avoid giving that shop any more of your money and have someone else do the work that'd be wise.

Also in general a failed head gasket diagnosis on a Gen3 Prius doesn't mean you instantly have to fix it. As long as the engine isn't running rough on start up and your coolant reservoir isn't going down very fast you can use the car for short trips around town, sometimes for years without much of an issue. Just don't push it too far because once the engine starts running rough you can ruin the dampener inside the transmission and that will get super expensive.

 

I doubt there is anything the mechanic or anyone could have done to create a hg problem.

I would get the car back and check the symptoms. As suggested, it may run fine for awhile or it may be time for a hg or engine. The risk is a smaller hg job could progress to an engine. Either way, shop around for an independent shop.

If it is a head gasket, odds are it was leaking an occasional small amount of coolant and sealing itself off everytime you started it. Normally this creates no codes but could have had a random start up rattle. But sitting for six weeks under the right conditions could aggravate a small leak enough to create a full blown hg leak that will create codes.

Or it could have been fouled plugs due to the gen3 liquids in the intake problem or several other reasons. Driving it yourself might tell the story.

 

178K miles. And presumably the EGR circuit (including intake manifold never cleaned)? You've done better than some to dodge head gasket failure this long. And Toyota's done squat, basically.

 

Makes me think the root of Toyota's denial is based on as long as the car gets at least 100K miles before headgasket blows, it's not their problem.

 

I guess this is a carb certified car and one of those funny States is why it went to the dealer for the converter I wouldn't have to do that here so makes a humongous difference you know $1,300 part versus $140