Prius heater not getting hot enough!

If you are measuring correctly (?) something is seriously wrong. Normally they will be around 185-200f the same as the two coolant temp sensors. The bottom radiator hose supplying the thermostat may be 10-15f less than the engine operating temp.

The smaller reservoir hoses are at engine operating temp and are visibly flowing through the reservoir when the engine is warmed up.

To emphasize how wrong 55-60f is on the four radiator lines, my v has been off for over 3.5 hours and those lines are still 92-95f as is the reservoir.

 

Perhaps you didn't drive it enough for the thermostat to open?

 

In post #54, you said that you were buying a new Toyota OEM water pump. Is that what you just installed?

Sorry I did not see your post #28, if I had, I would have responded to you.

 

If I remember correctly, the Gen 3 has a heat exchanger inside the exhaust, where the coolant lines run in a loop to rapidly heat the coolant to save on fuel while heating up the interior. In order to prevent the coolant from boiling away and over-pressuring the coolant system, there is a thermostatically controlled gate which diverts the exhaust once the coolant has reached a certain temperature. Yours may have malfunctioned.

 

It is unlikely that a stuck exhaust heat recirc valve would overheat the engine but a clogged radiator, bad water pump or improperly operating engine thermostat could.

The exhaust heat recirc system has a coolant temperature sensor that can be monitored with many apps including the "Car Scanner" app below. If the recirc system does not reduce its heat exchange as designed the left recirc sensor will be higher than the engine sensor.



The exhaust heat recirc system primarily adds heat to a small diameter, low flow coolant loop flowing through the heater, egr cooler, exhaust heat recirc, throttle body and the thermostat bypass port. This low flow loop allows some coolant flow.

During initial warmup the engine thermostat is closed and the big radiator hoses and the radiator are blocked.

So we have warm up flow from the water pump through the engine, to the heater, split from the heater out to the egr cooler AND to the exhaust recirc system. The split flows are combined again at the egr cooler output and return to the thermostat via the thermostat bypass port. A small portion of this flow is diverted to the throttle body to warm it up and returns to the thermostat bypass port.

As long as the thermostat is closed almost no flow goes through the radiator or coolant reservoir loop. If the thermostat does not open or the radiator is clogged it overheats the engine once it warms up.