Still losing coolant after head gasket

most people don't bother fixing the head gasket at 298k. you can buy another engine with less mileage for about $500 at salvage yards.

 

I agree it would have made more sense to install a used engine (and transaxle for that matter, while you are at it) considering the miles logged by your car.

Presumably the engine suffered some trauma which required the cylinder head gasket to be replaced, perhaps an overheating issue? The Prius engine, being all-aluminum, will not tolerate a significant overheating incident without permanent damage.

Have you had a compression or leak down test performed to see whether any mechanical issues remain with the engine? That is a quick way to assess the condition of the piston rings and cylinder head valves, as well as the seal provided by the new cylinder head gasket.

Is the check engine light on? If no, then the coolant heat recovery system canister is probably OK.

Is it possible that residual air remains in the heater core coolant loop? See my posts #22 and #42 in the following thread which explains how to drain and refill engine coolant. This is not a simple process due to the presence of the CHRS system and the need to invoke inspection mode to get the Prius engine to continuously run.

Changing engine coolant | Page 2 | PriusChat