Peter, the mechanics that
Peter, the mechanics that discouraged you from replacing the head gasket the gen 3 Prius sound like alarmists. If the engien runs fine at any time during your test, the main components are still good. A problem like a bent rod doesn't come and go. I've never seen a bent rod occur on startup. If enough coolant has leaked into the cylinder (hydrolock) to cause this kind of damage. The engine simply won't crank. It will just stop when it reaches the hydrolocked cylinder with its valves closed. The only time hydrolocking will bend a rod in a Prius engine is if a copious amount of coolant enters the cylinder while the engine is running and the piston has the momentum of the spinning crankshaft. And if a head gasket leak is so severe it could fill a cylinder within a few milliseconds, I doubt that engine would have been able to run at all. The only time this amount of coolant can enter the cylinder is while the engine is stopped and it slowly fills the cylinder. But again, the engine won't even crank. There are lots of mechanics who are afraid of head gasket jobs because of lack of confidence in their own ability. For some, it takes several dozen to gain that confidence. Some will never get over it. It's just easier on the brain to cover your butt and recommend an engine replacement. I've had old-timer mechanics who are so uncomfortable doing them, I'd have to reassign jobs.