Why isn't the coolont control valve covered under the hybrid warranty

The check engine light coming on shows that the problem is with the engine, not with the hybrid system.

The failed valve in question is most likely for the coolant heat recovery system which reduces engine exhaust emissions by speeding up engine warm-up. This valve is part of the engine coolant system, not the inverter coolant system.

The inverter/transaxle coolant system does not have valves in the coolant loop. In any event, the hybrid components warranty covers only those components that are specifically listed in the warranty terms.

 

Is this what we used to call a "thermostat" in the old days???

 

Well, the Prius gasoline engine has a thermostat located in the usual place.

The coolant canister stores ~3 quarts of hot coolant upon shutdown. When the car next has a cold start, the hot coolant is pumped into the engine, supposedly to speed up warmup.

I think this is way too much complexity for the benefit obtained, which is probably why that design was abandoned for 3G.

 

I love over engineering though. A hundred extra parts to squeeze out a few fractions of a percent of efficiency, is beautiful.