Weird Overheating Issue

Wondering why that would matter

 

Somebody read Mad Magazine as a child.....................and still does!!

 

I edited my post #20 by adding "I know this is not related to your overheating problem, I am just curious."

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I commend you on your troubleshooting process to monitor both of the temperature sensors.

My guess is that you still have some air trapped in the exhaust heat recovery coolant loop or what ChapmanF wrote in post #17 about the exhaust heat recovery thermostat maybe being the problem.

Can you please tell us in detail the process you used when you refilled the coolant and how you tried to bleed the air out of the engine coolant system.

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I checked my car tonight.


7C0 is the Exhaust Heat Recirculation Coolant Temp Sensor.



The Exhaust Heat Recirc piping cools off much faster than the engine block/head sensor and stayed 4-5 degrees cooler when the engine was fully warmed up.

 

Radiator cap on or off? I have done mine at least twenty times always with the cap off to release air.

Typically thermistors do not intermittently go higher on their own. Usually they open circuit or short. Even a bad connection normally won’t reduce accuracy by more than 1-2 degrees.

A quick check with a low cost infrared thermometer verifies the sensor against your scanner. Easy. My sensor was within three degrees of the scanner.



If the sensor checks out, odds are the piping at that measurement point is getting hotter. The flow diagram in post 25 suggests the Exhaust Heat Recirc valve may not be opening. If so, the coolant may be getting hotter.

 

As you have a Gen 3, which has a degas-bottle cooling system, there is a fairly straightforward procedure in the manual. When you look at the degas bottle, you will notice there is a line marked B, up above the line marked FULL.

When refilling a system, you fill right up to the B line, cap the bottle, start the engine, and run it long enough to be pressurized and hot, and several minutes after that. Some squishing and shaking of hoses is involved. Then you turn it off and wait for everything to cool.

Once everything has cooled back to ambient temperature, you look at the bottle again and see the level dropped down to the FULL line. The extra coolant in the bottle traded places with the air in the cooling system. The distance from FULL up to B is the amount of coolant the engineers knew it would take to do that.

All that said, I suspect "trapped air" gets blamed for strictly more cooling system issues than it's really capable of explaining, and this is probably the kind it wouldn't explain very well.

It's a thermistor sensor and those don't go bad a lot.

There's some troubleshooting information in the section of the repair manual for trouble code B1503; that's the code the combination meter sets if that temperature reading looks unreasonable. That sensor is wired straight to the combination meter, which is why it gets a B code instead of a P code like you'd expect to see from the engine.

The instructions for checking the exhaust flow control valve and its thermostatic actuator are earlier in the manual. That stuff is pretty easy to see, once you're under the car.

 

The instructions for checking the exhaust flow control valve and its thermostatic actuator are earlier in the manual. That stuff is pretty easy to see, once you're under the car.

Toyota Service Information and Where To Find It | PriusChat

The rod should be at least 7.2 mm further extended at operating temperature than at ambient.

That's probably ok, though if you ever do it again, to follow the manual you would have the cap on, so the system can reach pressure and make the bubbles smaller to work their way out.

 

You should also fill VERY SLOWLY.... A little at a time.
This allows the coolant to settle and push the air up and out.

If you fill slowly, eventually to the "B" mark on the tank. Let it sit for a few minutes then
top it off, you'll notice that it is at the full mark after it runs for a few minutes.

What I have done on my Prius is start the car, after filling coolant, let the engine run until it shuts off.
Check the level and it's right at the full mark. Then I drive the for a mile or two close to my house.
Then I park it level, clean everything up and then check the level. The 4(?) times I've it it has been at the
full mark or just below. I fill it just past the full mark and it stays there.

I've neve had an over heating problem.

Filling it fast traps the air.

 

I would bypass the coolant hoses to the exhaust and try it again.

 

I do not think that this helps very much in the diagnostics of his problem. It will only prove that coolant flowing through the exhaust heat recirulation loop does not get hot after you do the bypass. It will not prove that the actuator is sticking a little during the warming up phase.

 

I agree with your theory that the actuator is sticking a little during the warmup phase. Is there a way to keep the exhaust flow control valve in the open position? If so, try it and test drive the car and watch the coolant temperatures.

I would replace all the parts in the actuator assembly. You only want to do this once.

EDIT: The exhaust flow control valve maybe is not opening smoothly when the actuator is trying to open it. It might not be a sticky actuator.

 

I would bypass as the repair.

 

OK.

If you do the bypass, then the exhaust flow control valve will not open in the exhaust pipe. Will this cause any problems in the long run?

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You could replace the actuator and heat exchanger (valve is likely carbon clogged), force the valve open with a clamp or forget about it.

I would not buy parts until I knew the bypass fixed the overheat issue. The temperature sensor has not been verified or there could be a serious engine cooling issue.