Prius intermittent temp light when driving uphill

i'm no expert, but i would be worried. idk what temp sets the light, but it can't be a good thing

 

Did you install a Toyota OEM water pump or an aftermarket pump?

 

Certainly not normal with the noise and coolant running too hot.

 

Usually, the trapped air will bleed itself. In my old 1985 Corolla LE FWD, if air was trapped during coolant drain and refill, there would be no coolant circulation whatsoever. The solution was as easy as pumping the coolant by repeatedly squeezing and releasing the upper hose and then adding more coolant. Also, the jiggle valve on the thermostat, which helps bleed the coolant, needs to face up.

You use a 50/50 water/antifreeze mixture, right? Using a higher antifreeze concentration will result in a lower cooling efficiency and higher coolant temperatures.

Check for leaks and a bad radiator cap. If no leaks are found, it could be an improperly installed head gasket that is sucking air or perhaps a a bad or improperly installed water pump.

 

Comparing 1985 gasser car to a 2011 hybrid car for troubleshooting contrast, mice

 

You made it onto the archive.

 

206f on a steep hill in hot weather is ok. But you said 206+. Does that mean 240f or higher? Typically the light comes on at 248f.

Gen3 has two engine-coolant temperature sensors to monitor and either one can flash the light. One is on the engine while the other is on the hose coming from the exhaust heat recirc system. With Techstream one is in the ecm pids while the other is in the Combination Meter group. Both are called Coolant Temps.

As noted in a July 14th post, the exhaust recirc thermostat could be stuck in the heat exchanger position adding unnecessary heat after warmup. This was reported at least twice now. The engine temp could be fine but the exhaust heat exchanger sensor (Combination Meter ecu) could trigger the light.

I use the Car Scanner app to display both engine-coolant temps.



Normal capture of both temps (Exhaust Heat Coolant Temp in Red)


Overheat light caused by a stuck exhaust heat recirc valve. (Exhaust Heat Coolant Temp in Red)


In the above Car Scanner capture the red trend exceeds the other sensor but not enough to trip the warning light in this test run. However the owner MSB87 replaced parts of the exhaust heat recirc system and eliminated the problem.

 

Did not compare. That was only a mention in a lengthy post. He likely has an air leak, which could be from the head gasket or water pump as I explained.

 

But the coolant is bubbling, which means there is an air leak unless there is an unlikely air-bleed issue.

 

Engine vacuum changes when you release the accelerator pedal (an increase in vacuum) and also when you activate the brake booster (a decrease in vacuum). So, it does sound like the engine is sucking in air through the newly replaced head gasket and it is mixing with the coolant.

Check to see if the coolant is mixed into the oil. You can do so by a used-oil analysis, which you can order through Blackstone Laboratories or other oil-analysis places. You should put a note to check for antifreeze when you place the order.

Oil analysis | Blackstone Laboratories

https://wearcheck.com/

 

You still have not mentioned exactly how hot it gets. Are there any codes? For the light to go on requires higher than 206f.

Has the coolant been low requiring topping off?

If there is air in the system it typically accumulates in the reservoir and is released. A gen3 normally does not trap coolant in heater lines where it might be heard "bubbling" in the cabin.

However if there is a head gasket leak again (not unheard of) then combustion gasses may continuously inject into the coolant.

The temperature light is concerning and could be caused by low capacity due to previous sealer clogging the radiator, low coolant, weak water pump, or a bad thermostat.

If it is losing coolant that is not a good sign. Regardless I would get a monitor capable of displaying both coolant temperatures and see what is happening. Both should closely track each other. Low cooling system capacity may show higher than normal temperatures without a steep hill climb.