No Heat After Multiple Tries? Gen2 07

You should make sure your hoses are not crossed and connected correctly. It takes a while to properly bleed the coolant. Check a few hours after driving the car and make sure the radiator is full (don't do it when it's hot). You may have to fill the radiator a few times before the coolant level is full. Then check your heat and see if you have heat.

 

Monitor your coolant temperature and check your coolant pump, radiator for cold spots, both upper and lower radiator hoses should get warm warm to hot if circulating properly. Has the thermostat been replaced and how many miles on it?
If you haven't been changing coolant per OEM specifications, that flush may've knocked something loose and is blocking proper coolant circulation within your system.

Good Luck.....

 

Review these two videos and make sure you didn't skip any steps:

I second the suggestion to check the hoses. It is possible to hook them up wrong and take part of the cooling loop out of action.

 

Here's a diagram.

I assume that if the engine doesn't overheat, then the water pump and drive belt are ok? Is that true?

If one hose is warm but the second is cooler, then the heater flow is restricted - could be kinked hose, airbound, or clogged core (I don't see cloggs often on Toyotas).

If both hoses for the heater core are warm but the heater air is cold then something might be wrong with the temperature blend door operation.

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Did you check the pump that is specifically for the heater? This car has a lot of fluid pumps, there are 3 in the ICE cooling system. I agree that the car would probably overheat if the mechanically driven pump had failed, but I think that only the heat will go out if the little electric pump that moves fluid through the heater core was dead.

Are you sure that the blend door is working?

Presumably you can flush the heater core like any other sort of device with a fluid inlet and outlet. However, it might not be a bad idea to post flush it with distilled water before reattaching it to the coolant loop. At least if you have the same sort of incredibly hard water that we do. All those minerals might not play nicely with the Toyota coolant.

 

Please read this thread if you have not already done so:

No heat - what's next? | PriusChat

Regarding the electric pump for the heat. While that is only needed when the ICE motor isn't going (so that the belt driven water pump is inactive) it can still be the problem. If it is clogged with some foreign substance then the coolant cannot get through it. There is some suspicion that cars with the foam rubber bits in the coolant get those from a damaged thermos. The theory being that the thermos has foam between two pieces of metal, but if it is smashed in a wreck while the ICE motor is running the inner metal can be breached, foam breaks off and enters the coolant, and ends up all through the ICE cooling system.

No heat in cabin, ended up being foam stuck in heater core pump! | PriusChat

The other possibility is that the car at some point either had a leaky radiator or head gasket, and somebody put stop leak into it. That is a common cause for heater cores to stop working (in general, not just this car.)

It would be odd though for either the foam rubber bits or stop leaks problems to wait 7 years after you bought the car to show up.

In this article:

Mastering the Gen 2 Prius Engine Cooling System - Automotive Tech Info

they note that the 3 way valve can fail in such a way that there is no heat to the cabin. There are apparently two PIDs, one to set the position and one to read it. So with the proper hardware/software you can test the valve and verify that it is working. Techstream would be the tool most of us would use for this.

 

The best explanation of the ICE cooling system, complete with arrows to show what flows where, that I have found is here:

How The Same Technology That Keeps Your Hot Chocolate Warm Reduces Emissions On The Second-Generation Toyota Prius - The Autopian

In particular, this image from the article:


suggests that after the car has warmed up the hose to the 3 way valve should be hot. If it isn't then something in that loop (follow the arrows) is jammed. That could be within the motor itself, near that outlet port. You have already ruled out the heater core itself. Was the motor itself ever flushed? I have lost track.

If both hoses at the heater core are hot then there is a problem with the blend door, either something mechanical, or more likely, the actuator has failed.

 

Sorry this is happening. Have you tried the approach suggested here?

No Cabin Heat After Coolant Flow Control Valve Replaced, 2008 | PriusChat

It might not work, but at least it is an easy thing to try and you don't even have to get your hands dirty.

Review how they did the "professional flush". Did it involve forcing fluid through the outlet at the motor that goes through a hose directly to the 3 way valve? I give even odds that the flush was just for the motor and the loop including the radiator.

I think the most likely place for something to jam is in the loop from that outlet to the inlet at the thermostat, rather than in the motor. Not the big inlet from the radiator, the other one near it. In fact, looking at the loop, perhaps that inlet itself is jammed with something. I have not laid eyes on it personally, but I would expect that it is a much smaller opening than the one from the radiator, perhaps small enough to catch a piece of rubber or other contaminant.

After the car has been driven for a while, and then turned off, and immediately after the thermos motor has made its racket, is the inlet hose to the thermos hot? If not then the problem is upstream from there. Probably. Wait, that logic is wrong, but it would be a helpful piece of information.

 

Right side heater core hose is hot?????

If the coolant is moving in a hose the temperature along it should be relatively constant. If heat is moving only through convection and diffusion there is likely to be a pretty big gradient. If the left side heater core hose is accessible enough to get temperature measurements, it might be helpful to get one at the midpoint and the two endpoints. You may not need to get a hand on it, just a clear path to it, if you have an IR temperature gun, like this:

12:1 Infrared Laser Thermometer

You may want to contact that service department and find out exactly what they did for that flush.

 

Well, let's think about that.

"Cold weather models" had two 400W PTC heaters in the dash, one in the heater core and one in the air duct. See the "air conditioning" section of the repair manual. Both are driven by a "PTC relay". I believe this system is only supposed to be active up until the time the ICE has warmed up. If this is what is causing the warm air pulling the "PTC relay", wherever that is, should turn off that little bit of heat.

Climate control set to provide heat, cabin fan running, car on and warmed up.

Engine on: Mechanical water pump on, electric pump for heater core off.
Engine off: Mechanical water pump off, electric pump for heater core on.

We know the mechanical water pump works because the car isn't overheating. (So it is pushing hot coolant through the radiator, but possibly not out the outlet that goes to the 3 way valve.) So that suggests that somehow when the electric pump is turned on it gets a little hot coolant (because warm, not hot) into the heater core, but it doesn't when just the mechanical pump is running. Which would be very strange, but there we are. That predicts that if this is what is happening the inlet hose on the heater core should warm up under these conditions and cool off again when the ICE motor shuts off.

Just thinking out loud here. Imagine there is something stuck in the inlet or inside the coolant control valve, which mostly blocks flow. When the mechanical pump is running the blocked fluid backs up and can go around through the radiator or through the bypass passage. However, when the electric pump is running it can only move fluid through the coolant control valve, past whatever that blockage is. Because of its position, the electric pump is more effective for moving coolant into the core in this scenario. Even though it isn't all that great either (because warm, not hot). The blockage could also be in the hose leading to the pump, or inside the motor near that outlet, or maybe even stuck in the heater core. Check the full length of the hose from the motor to the valve, maybe it is pinched or kinked somehow? That would do the same thing as a blockage.