Very initial stages of investigation: Prius v at 250k+ miles. Coolant slowly going down. No noticeable white smoke. MPG doing fine, at least lately. Car started making a brief rumble or shake, becoming more frequent (maybe once per trip). Sometimes at startup and stop-and-go traffic. Now code P0301. What are the odds this is head gasket failure?
Pretty good. Do an egr block to eliminate a sticking egr valve (however egr would not cause loss of coolant) or move straight to a high quality articulating borescope when cold with the coolant pressurized. Car Care Nut HG Borescope at 660s Egr block flow test https://youtu.be/lFVNaDJ6HOI?si=lZjJK932oimbrx8R&t=238 At about 10:15 in the video he starts talking about the egr valve letting "air" into the intake manifold. He means exhaust gasses.
Would your guess be that it's in the early stages? My average MPG has actually being creeping up by tenths over the last few months. Moreover, I've owned the vehicle for 15-16 months but had it for about a year before noticing low coolant.
You ever monitor the ECT while traveling? Hopefully the previous owner didn't put 'stop-leak' into it to cover-up that issue.Has that electronic water pump ever been changed? If it turns out to be the HG; the engine may have been 'running hot' and popped that HG.
Normally early stages are very occasional severe rattles without coolant loss. I would do something asap because of possible overheating, warped heads, bent connecting rods or worse. The famous "Hey Walt" video
Right, I never requested a full Carfax report from the dealer. It was originally a CA car; I'm in MN. It would be good to know about service history. Would a failed water pump throw a code? And do Priuses not have an indicator light for engine overheating?
Prius gen3 engines do have an overheating light but it is often momentary with low coolant. Monitoring the engine temperature with an aftermarket reader is useful before problems exist to possibly see normal 185-205f coolant temperatures move up. Sometimes they don't move up to the light's 248f setpoint, which again, can be momentary and missed with low coolant. No overheating code usually appears but a misfire code is common when you are past the early stages. Water pump codes can be stored but there are some "impeller dragging" situations where water pump codes do not occur.
See that was previously disclosed, should read more carefully. Any 3rd gen or v, for sale with 220k miles, there's a decent chance it's being dumped with a stop-leak product in the engine coolant.
The Prius doesn't save or log over-temperature. The water pump will only throw a code if it there's a dead short or open in the current pathway. So if it's intermittently stalling, you won't know unless you notice the temp lamp flashing. PS; there's no accompanying alarm or beep sounds when this happens - you just need to notice it. A 3nd party HUD that plugs into your OBD2 port will remedy this.
