Heater not blowing hot enough

In a generation too your water control valve may be acting up It's on the driver side right behind the radiator just a little bit below the level of the inverter I think it might be called the three-way coolant control valve they are known to get weird at high mileage and I believe this can affect your heat It also can be that the damper door in the car that opens and allows air to go across the heater core and into the car for your heat also have problems at high mileage The metal from the potentiometer that controls it and gets a little foo bar and you may be able to clean it or you may have to replace it If you get down and look up above the plastics near where the steering mechanism is this device the air damper door is up in that area somewhere I think and there are some posts in this Prius chat with pictures of the whiskers and the stuff that get in the system that have to be cleaned replaced something It's similar to cleaning old stereo volume knobs if you remember anything about that. Good luck won't take much to get it straight

 

Gen 2 has a belt-driven engine water pump, so it stops when the engine does. There is a separate electric water pump back by the firewall that has to kick in to keep the cabin heat flowing when the engine is stopped. Has that pump been checked?

 

The pump is part 87200-47030 and it is back near the firewall, within one short hose of the heater core fittings. Callout 87200A here:

With two thermocouples, you could clamp one to each fitting of the heater core, and measure the temperature difference, how much it drops between the supply and the return, with the heater blower on high. It would be hard to interpret without comparing to the same results in another Gen 2 with satisfactory heat, in the same conditions.

If it is hot when the engine runs and not when the engine is stopped, I would still lean more toward something like that pump. A clogged core will be clogged the same when the engine runs or stops.

 

That's the pump I took off of another car to use as my inverter pump on my '09 That's the pump that's rated at 14 volts The one in the fender well that looks the same for the heat recovery coolant system is marked 12 volt and thus has a different part number but the same plug and they will both run on 12 volt Not sure why the different stickers are on them I have several of these laying in a box here now when my inverter pump goes in one of the other generation twos I used the firewall mounted to the brake actuator plate as my inverter pump. I would be interested to know if that pump is failed also should be interesting to note because this pump usually pretty much last forever it's very well built . That's why it didn't cross my mind in the response because I've never seen one burnt up blown up or not operating I have seen the same exact pump with the different voltage marking in the fender on the left side for the heat recovery tank I've seen many of those bad I've plugged them up and watched them go bad I don't know why they both look exactly the same. And I wouldn't think plugging of a heater core or the radiator for that matter would cause the symptoms you have unless what's clogging is able to move which usually isn't the case. But that's a good call on the pump which I'm not understanding how that could really be anyway because anytime I have my heat on the engine predominantly runs If I come to a stop sign and I don't have the heater on I just have flow through ventilation heat comes out the vents because the car is moving that type of thing. And I stop at a stop sign and then there's no heat coming out If I put the heat to on and put the fan on say medium the engine will immediately start up I guess because of the call for heat I don't know It does it in all of my generation twos and they all have excellent heat they will run you out of the car. Matter of fact I don't even turn my heat on most of the time I leave it off it said it high then everything is turned off and the screen is in the consumption mode I have no fan on but air comes out the vents when I'm moving forward If I get on the highway it can get so hot in the car I have to open a window with no fan running.

 

It really helps to have tools to measure temperatures. They make dial gauge thermometers to read HVAC air duct temps. What's the reading with ICE running vs not? I might expect some difference even with a restricted core if the electric pump is much "weaker" than the mechanical pump.

Testing the electric pump is easy if you have a capable scantool with bidirectional controls. If I recall, you have to go into the Hybrid Control module to find that test.

They also make non contact InfraRed pyrometers.

For a good heater core, I typically see no more than a 20°F drop across the heater hoses (with ICE running). More than that usually indicates a restriction.


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Those non-contact IR tools can be very easy to misinterpret for this kind of thing. Are you reading off the aluminum pipe nipple of the heater core, or off the matte black of a hose that's attached there? Or off some thin black tape you wrapped around the aluminum pipe to increase the emissivity? How thick is the hose? What value for emissivity do you plug in to your IR gun (if it allows you to set that)? If it doesn't let you set that, what fixed emissivity is it assuming?

You might work up to getting pretty repeatable results if these are measurements you make really often, the same way, on the same kinds of cars, and for a while you were carefully cross-checking against a thermocouple, but otherwise you could easily end up fooling yourself with readings that are really all over the map.

 

True enough. Lots of limitations with an IR gun. But it's reasonably priced and good enough to get a temperature differential for two hoses.

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I gave up on a similar mission with mine once. Readings just too all over the place.

 

Actually in most of these situations I'm usually just using my hand on a regular car I can run my hand across the heater core to feel for hot spots in the middle or somebody's put that stop leak in the radiator or in the system I can feel in and out on the main hoses going to the engine whichever engine it is etc etc. I rarely take the fluke heat IR gun off the hanger it hangs on. The extra hoses in the coolant heat storage tank on the Gen 2 make this a lot of fun.

 

At first glance I thought your message said "Hunter not blowing hot enough" LMAO

 

I just had to change the two front fenders in the bumper cover on the '09 where I put the heater booster pump as my inverter pump to pictures of it again yesterday it's still working fine just sitting there and it looks like it'll be there a long time .added some wiring for fog drl lights . Now it looks like a cab or a Hurst Olds w30 from about 1976 gold and black colors the parts I got from a mint condition black car they look really good I'm glad I did not for the hood so it's a gold car with black front fenders and front bumper cover I might go back and get the doors because I can get them for basically free and they're all four of them are perfect but I may not.

 

Maybe the coolant control valve right there to the side of the left headlight and behind the radiator or the radiator support It's the other coolant valve.

 

I don't know usually you have codes It could be just simply an air bubble Do you feel the heater hoses getting hot? I guess you're not getting any coolant heat storage tank codes or what have you so probably no need to look anywhere around there after you go out for a good run not necessarily speeding so much but a good long run 45 minutes something Is the car getting hot I don't know whether you have a temp gun or experienced hands or what have you but you know you're looking to see if you're car is actually warming up but the Prius all of my Prius have ridiculous heat I don't care how cold it is outside it'll run you out of the car unless you're you know like in your pajamas and slippers then it's very comfortable but if you're in your outdoor clothes you have to turn that sucker down quick I don't turn it up to begin with is generally how it works but plenty of heat.

 

Usually when the three-way valve or coolant control valve goes bad there is codes involved and it'll make a funny noise that awkward times things like that I personally have not had to replace one yet so I'm either getting cars where that's already been dealt with or I'm just lucky same with water pumps people say these water pumps on the generation2 are finicky. I just seem like standard old 1.3 l k e engine water pumps actually and usually my experiences they've been they last for life or well into the hundreds of thousands of miles usually and when they don't you just slap on another one it's mechanical has a belt nothing to it But that wouldn't be any part of your heat problem your water pump will be leaking or something but it won't really actually stop pumping unless the belt is broken.