Air bubbles in 2012 toyota prius coolant system

What brand engine water pump did you buy and install last year?

What brand engine water pump and thermostat did you buy and install last week?

It sounds like the water pump you just installed is not working correctly.

 

A lot of the time I just point out what the car's engineers said to do, without trying to second-guess why they said it. They say to do the warmup with the cap on, so that's the way I do it, and I haven't had a problem.

If I had to guess why, well, with the cap on, the system's normal operating pressure is close to the 108 kPa marked on the cap (in absolute terms, about twice atmospheric pressure). With the cap off, you've only got atmospheric pressure. Any bubbles are half as big with the cap on, may move through the hoses more readily.

I'm not positive what you did "didn't work"; there may be explanations besides "air bubbles" for why your car overheats.

 

Bingo! I think the engine is overheating, which is causing the coolant to boil, and you see "air" pockets being pushed through the hose back to the plastic reservoir.

 

If the car overheats while running at high speed or climbing hills and does not overheat at slower speeds, your engine water pump is not working correctly.

Are you using the scanner to monitor the engine coolant temperature?

 

The boiling point of 50/50 glycol is pretty high though, especially under pressure—definitely above the temperature where the light comes on—so this would make the most sense if the bubbles are only seen after that light appears.

Another source of perpetual bubbles could be exhaust gas coming through a head gasket; those might be seen even before the coolant gets as hot as all that.

 

If you don’t lose coolant level when bubbles are coming out, it is unlikely to be entrained air from new fluid introduction. The gas could be combustion. Get a combustion gas tester at the auto supply and check it.

I have changed my 300,000 v coolant at least ten times and never pulled off anything. I used maintenance mode with the cap off a few times but now just start the engine normally with the cap off and the heat on ‘hi’. Bubbles come out, cap it and go. I then drive it and check.

Obviously I watch coolant level and oil at least every fillup because of this engine design.

How hot does it get? Higher than 210f?

On these cars you do not normally lose fluid in the early stages of hg leaks as they seal quickly. The characteristic rattle is extremely random even on multiple cold starts for weeks. Probably a function of valves closed on shutdown.

Questions:

1. How hot does it get while driving?

2. Do the radiator fans work?

 

Are you saying that you purchased a brand new OEM water pump from a Toyota dealership last week, and you installed it and the engine is still overheating?

Or, are you saying that you replaced the water pump last year with an Aisin pump and replaced the thermostat last week. Where did you buy the Aisin pump from?

Your problem is definitely with the water pump and not with air bubbles trapped in the cooling system.

 

Why did you replace the thermostat last week if you were not having any problems with it?

Did you buy the thermostat from a Toyota dealership.

 

See my post #23 for my response.