Heatup Issue

is it possible that all the air wasn't evacuated from the coolant? i have read that it can be tricky

 

That's kind of late in the day; how clogged was it?

Is it stable too, not dropping?

 

Time to burp the baby or it's gonna start crying!

 

First 96c is normal. 99c is only slightly hotter at 210f and may set off the steady warning where a shutdown is advised. Flashing is trouble.

Water pump is likely. Normally you can see movement in the reservoir after it warms up. Usually there will be water pump codes.

The thermostat is possible but not as likely. This could also stop the reservoir flow.

Failing head gasket or a coolant leak would mean the coolant level in the reservoir would be low. A bad coolant cap could be releasing fluid as well.

This is a significant threat to the aluminum engine. Don't guess or wait.

 

What did you use to check codes?

I ask because there are things in the car besides the engine that can light the overheat light, and your engine wasn't hot enough to light it. For the engine, that light comes on at 120 ℃ (248 ℉), still above what your gauge is showing. But in your post, I don't see the temperatures of the inverter or motor-generators.

Those other things typically set codes when they overheat, but those codes are in the power management control ECU, which many generic scan tools will miss.

(Also, the engine has two temperature sensors, one that's wired to the ECM and one that's wired straight to the combination meter. If the one wired to the CM overheats, a B1503 code is set, but again, that's in the combination meter, where some scan tools will miss it.)

 

May also be a clogged/dirty radiator.. checking the simple stuff first might be a good idea

 

I also have B1503 error code; it also stated combination meter /Exhaust heat management warning Detected, I started having issue on freeway, it overheated, if you try and start now it runs very rough and shakes, it's a 2012 toyota prius plug in, any ideas on what it could be??

 

Go to Google and type this in so your results look like image below and start reading...

Prius 2010-15 related posts apply to your vehicle:

 

I wish more of those threads mentioned right up front that B1503 does not refer to the coolant temperature sensor that's screwed into the cylinder head (that one's wired to the ECM), but to the other coolant temperature sensor that screws into the tee fitting in the rubber hose at the back of the engine bay, where the coolant comes back up from the exhaust heat exchanger. That one's wired straight to the combination meter.

Either one can make the overheat light come on, either directly for this one, or via a message to the combination meter from the ECM for the other one.

It could mean either that the temperature really is 120 ℃ or above, or that the sensor or wiring have a problem that makes the reading appear weirdly low or high.

If you could look at the ECM's idea of the coolant temperature, from the other sensor, at around the same time, that might help fill in the picture. I might suspect a wiring problem if this sensor is reading 120 ℃ or above while the cylinder head sensor isn't looking at least kind of hot. On the other hand, if both sensors are reading hot, I'd be a believer.