2011 Prius overheated - warm air taking longer to come out vents

I've been fighting this on a generation 2 for about a month now You got an air bubble floating around in your system or you're actually losing coolant and you don't know from where and when the coolant gets down just about it 3 oz coolant will not make the loop and you have no heat mine does this 40 minutes after filling the system I go for a drive for 40 minutes The hosees get hard as basketballs and everything seems to be fine The bottom hose is warm and so on and while I'm driving in this first 45 minutes the heat will go from blazing hot like it does in my other three cars and it will turn cold while I'm driving and I get out all the hoses are hard everything seems fine apparently I've either lost coolant or an air bubble has developed and I have no heat the overheating triangle and the little car with the thermostat showing which is different than yours comes on every 30 seconds and goes right back off It's like the air bubble gets over the heat sensor in the engine causes the lights to come on and the little thermostat to show then it moves and it goes off My engine is not overheating I don't think yours is either and that's where you are That's where I am right now I just filled up again yesterday and ran through all the tests and everything is still the same and all of a sudden I'm not getting my overheating and triangle coming up and my heat is stayed on for almost 2 hours so tonight when I get home and park it and the pressure comes down I take the cap off and if I don't see coolant at the top of the radiator neck that's a problem because that's where I left it when I completely filled it so I add coolant until it brings it up to the top of the neck. And I sit there and watch and I watch it drop and I keep doing this until it will not falter down the neck and it sits right at the hole getting ready to go to the reservoir then I go in the house and leave it. When I come out in the morning 9 hours later the coolant has dropped down the neck again but if I squeeze one of the main radiator hoses it rises up and I see the water at the top of the neck so again I had water to the top of the neck put the jug down take one of my other cars and go on about my day 5 hours when I come back the water will be down again to the same exact place I squeeze on the hose same thing again I can't find the leak in this vehicle anywhere not a drop not a permeated hose nothing there's no water in the oil nothing and this is not a damper door that's moving out of the way and changing me from hot to cold air no sir that's not what's happening The hose is going to the heater core are cold or one is slightly warm and the other ones dead cold so there's no flow I have a mechanical water pump not electric so I don't think my mechanical pump is the problem your electric could be but usually you can call that up with software and watch it work Good luck.

 

Those electric water pumps tend to get intermittent, then fail outright. I'd shot-gun it, with that kind of mileage on her, water pump, thermostat, coolant.
FWIW, your overheat issue would be readily apparent in the summer months, climbing the hills and mountains in your area. If you read the footnotes of your maintenance manual; coolant change is suppose to be done every 50K after the initial 100K+ coolant change. You should probably flush out the brake fluid system too, if that hasn't been done.

Good Luck....

BTW; You never want to see the temperature lamp light up in these cars. When they do, your ECT is in excess of around 240F - hot enough for things to start breaking. There's a lot of plastic bits in these modern cars, plastic and heat don't mix well - just saying....

 

The loop that runs through the cabin heater runs past the thermostat, not through it, precisely so you can start having cabin heat before the engine is at full temperature and the stat opens. (In fact, that bypass flow is what makes sure there is hot coolant flowing around the thermostat so it can sense when to open.)

The idea of an intermittent water pump problem sounds worth looking into. A suitable scan tool can log the water pump rpm.

 

I don't think you're going to get a water pump code until the impeller starts chunking out enough and causing a flow problem which is I think what the 261B is right insufficient water flow or coolant being pumped or something along those lines so if you're moving just enough to almost get you by it may not throw that code but looking at the freeze frame data of the RPM the pump is trying to turn and what it might actually be turning is something else by now if this is your original pump you're impeller should be peeling the plastic when you remove it you'll see it this takes 30 minutes find somewhere for the coolant to go a container and undo a couple bolts You may or may not have to set the air conditioning compressor aside I can't remember exactly but it was very quick the bolts on the air conditioning compressor without evacuating it a couple minutes best they're 14 mm I think kind of long and then the compressor can just hang you know go down towards the ground and sit there and that gives you a bird's-eye view of your water pump of course you have the noise filter off of the air filter box and that stuff out of the way no issue soon as you pull that impeller out you should see the white plastic peeling off the impeller and you may not be able to turn the impeller by hand or it'll go a little bit and then stop something like that that's what your motor is trying to do with it goes a little bit and stops maybe goes a little bit and stops now while it's disassembled you can plug it back up to the car stick the impeller in its hole call it up with tis keeping your finger on the center of the impeller so it doesn't try to fly out see if it turns when it's called for by the software sitting in your hand essentially unplugged up so you'll have to hold it down low like it's in the car I bet the thing barely turns might be your solel problem

 

Your engine water pump can be turning slower than it should be turning, and it will not trigger a P261B code. When the pump is turning slower, less water is pumped through the engine, and the engine overheats. The overheating will occur when using more throttle, like going up a hill or at highway speeds. You should replace the water pump ASAP. If you plan on keeping the car for more than a year, get the Toyota OEM pump. Cheap aftermarket pumps only last about one year.

 

@Prius @Todd (boy, that username does not want to auto-complete):

To your knowledge has the water pump (and/or the thermostat) ever been replaced? If not I wouldn't hesitate to do both. Genuine Aisin WPT-190 is the pump Toyota sources, maybe a bit cheaper.

The consensus here seems to be replace by 150k (miles). 100K is safer still: there's been quite a few reports of failure by 150K.

Buy Genuine Toyota 161A029015 (161A0-29015) Pump Assy, Engine Water. Prices, fast shipping, photos, weight - Amayama

 

That's OK, he can wait for the code to pop up - In the mean time the car will be running above 200F, so we can take bets on which will go first. Head gasket, another code or something else..

This kinda reminds me of people driving off the road or into a lake while they were following their GPS. The software code is written by people, we all make mistakes, If the computer sees certain things, it will throw certain codes. If certain parameters aren't violated, no codes are thrown. This is also limited by sensor placement and types of sensor information available to the cars ECU.

 

The threshold shown in the repair manual for setting P261B is the water pump doing less than 900 RPM. I don't know that you get the code if it's doing more than 900 but less than the ECM's target water pump RPM.

You can watch both the target and the actual pump RPM on a suitable scan tool.

 

It’s hearsay, don’t know conclusively, but Aisin apparently makes the Toyota boxed pump, the only difference being the housing casting has additional text saying “TOYOTA”.