No Heat: Coolant Pumps During Main Mode, Not While Running

This is for a 2011 with 215K on the dash.

Heat went out a week ago. To troubleshoot, I:

1. Backflushed the heater core with 2 gallons of water/white vinegar. Some debris came out which appeared to be from some head gasket sealer, but all in all, it was not so bad.
   
   
2. Hand-pumped about 2 gallon through the system and back into the reservoir to check for any obvious debris or blockages, but the coolant appeared ok except for some air bubbles.
   
   
3. Bled the coolant by elevating the corner with the reservoir on the jack, then running maintenance mode through 2 fan cycles (approx 25-30 mins) with the cap off. Significant air was expelled in the first cycle with little to none in the second. The coolant flow seemed to indicate that the water pump and thermostat are functioning adequately. I then closed the cap back up and drove on the interstate for 6 miles, turned on the heat, and drove back another 6. Still no heat.
   
   
4. After cooling down enough to remove the tray under the wipers (~30 mins), started the car and turned the heater up to 80. The blower cranked up to like 5 out of 7 bars, but was still blowing cold air. The ICE only came on for about 2 mins before shutting back off. I felt both hoses get a little warmer - the input warmer than the output - but not like "hot." Most notably, watching the coolant reservoir, I never saw the coolant getting pumped. Typically, the blower speed lags when the motor is cold until it has a chance to reach sufficient temperature, but the blower came on immediately at 3 bars with the climate control set to 72, even though the car had sat for at least a half hour while I took the front end apart.

On the Reddit - as I've seen in this forum as well - someone suggested that the water pump can "partially fail." Could a partial failure of the water pump cause it to run in maintenance mode, but not during normal operation? And if so, should my next step be to replace the water pump (and thermostat?)? Or, is there something else that is more likely the culprit for my lack of heat (heater core valve? blend door? temperature sensor?)?

As I bought the vehicle used, I don't know when/if the water pump may have been replaced previously.

 

Thank you all for your replies!

You're talking about the "blend door"? How would I test that?

I alread dug out my old knockoff Techstream cable to try to test this, but I need to get it to play nice with Windows 11. Anyone managed this?

Are you saying a clogged radiator could cause the heater to stop working, or do you mean the heater core?

Yes, sorry, I know it is a sin, but seemed a lesser sin than the "earthquake in an anvil factory" that was happening otherwise.

Ok, but like I said, I backflushed the heater core with 2 gallons of water/white vinegar, and while some debris did come out, it wasn't significant and it ran clear by the end.

Ok, but like I said, I only saw the coolant flowing when in maintenance mode, and not while idling with the heat on.

Do you mean "the top hose"? Looking through the side of the reservoir, I can see when the coolant is and isn't flowing from the top hose. How would someone do this from the bottom hose?

I'm not sure I follow. If I leave the temperature constant and push the "mode" button to cycle through, I can hear the actuator, but that is to route the air between the floor, vents, etc., isn't it, and not the blend door? Alternatively, if I leave the mode constant and cycle the temp from "hi" to "lo," I don't think I hear anything.

Does that mean it's the blend door?

 

UPDATE: Last night, I was headed down the interstate when I got a "Check Hybrid System" on the dash - along with a bunch of other lights - which eventually shut any power to the wheels down. After letting it sit, I limped it off the interstate to a gas station where I pulled the ground wire to reset the computer. After that, I drove it 12 miles (on surface streets) without codes or other issues, idled it overnight (I'm a Prius-dwelling nomad), and drove it an additional 15 miles today, still with no codes or other incident.



Additionally, I took it to AutoZone and had them test the 12V for good measure.

Thank you for additional responses, which I will address...

I guess it's all relative, and certainly compared to working on my old 3 series BMW...

The horror... the horror...

:: Adagio for Strings plays while thousand yard stare ::

I mean, I'd love to, but it seems to be holding for now :: crosses fingers :: and I'll be in a much better place to address it if I can get some heat in the meantime!

Exactly - at the ports that pass through the firewall.

Not by me. Are you recommending I do so?

Mercy! I don't even know which version of the cable I have at this point, and probably need to start from scratch, if I go that route.

I assume these are sellers you're referencing? Where's the best place to start (over) for an aftermarket Techstream?

Ok, granted. As I said, however, I hand-pumped coolant through the return hose into the reservoir without much effort, as well as I see the coolant flowing when in maintenance mode, but not under normal conditions with the heater on. What about this makes you think there's a clog (as opposed to needing a new water pump)?

On this I think we've found agreement (assuming that "coolant pump" and "water pump" are the same thing). Except, if I'm going in there, ideally I'd like to flush, drain, replace the water pump and thermostat, refill, pray a decade of the rosary, and see what happens.

 

For the sake of clarity, when I backflushed the heater core, there was debris which came out. While this debris could have been clogging the heater core, it also could have been free-floating through with the coolant. I can't say.

That makes sense, and I suspect that may be the case, based on twice when running maintenance mode and getting a harsh, squealing noise after some time.

Yes, it's true, I have not yet found a sentient stop leak product (but give it a few years and maybe... ).

As I understand it, stop leak for head gaskets is typically based on suspending silica in the coolant. Therefore it remains fluid except where the coolant encounters exhaust gasses, which evaporate the coolant, leaving the silica to harden into glass - no sentience required.

That having been said, I think there's a possibility that even under this assumption, some lesser amount of coolant could evaporate, allowing some amount of silica to congeal without blocking the hole for which it was intended, or could break off after forming at the hole for which it was intended, leaving a larger clump floating in the coolant line which could then create a clog.

All accurate except that I could afford the repairs, if I had to. However... can anyone truly afford to pass on an opportunity to evolve herself through the process of DIY Prius repairs? :: rubs chin ponderingly ::

Thank you for the concern. I'm happy to report that visual inspection confirmed the presence of my cat.

Thank you for the recommendation. But why not the OBDLink MX+?

Ok, now I think you might be trolling me. I mean, why just replace the motor, and not the whole vehicle?

 

Please excuse me that I wasn't more clear earlier.

What I mean to say is that when I weigh my options, this is what I see:

1. Buy a (2024) new Prius - Yay, it's new, but depreciation, etc.
2. Buy a recent used Prius - a quick check of CL shows a 2019 for $20K and another one for $5K down, both with remaining powertrain warranty periods.
3. Buy an older used Prius - I see some still available for under $3K.
   
4. Replace the motor - costs as much or more as a down payment on something that still has a warranty, and maybe twice as much as rolling the dice on another used Gen 2 or 3, while still being a roll of the dice as well.
5. Bars Leak it for as long as I can - this may last only a few weeks, but it's also only $20 a shot. It may mean more frequent water pump changes and ultimately destroy the motor, but may be mitigated by chasing the Blue Devil with an oil change and coolant flush and change.

Than again, a new head gasket may take care of everything... until it goes out as well... assuming the head isn't warped... or cracked... or the block...

It just seems to me to go for the simplest fix and see how it holds. And if it doesn't, i just can't see replacing the motor, when the replacement could be just a few months away from the same result that could happen from Bars Leak.

Options 3-5 all seem like a roll of the dice. So if I'm rolling, I'll put $20 more Blue Devil in it, until I see how that goes, and then save the motor money to use as a down payment on something with a remaining powertrain warranty.

 

... unless, of course, I find one of those little, independent, Prius mechanics who can do the job for under $4K... which I did, and now I will have to add a review of ISH Hybrids to let others know.

And yet :: overly dramatic pause :: I still have no heat.

So, I guess I'll go looking for more info on the blend door...

EDIT: ... and I'll find so very little about it, that I'm halfway convinced it's a conspiracy - no videos on YT, and no explanations on here or elsewhere.

So my question is: have I just somehow overlooked them, or is this something that is probably beyond my skill level, and before I travel onward, I should see about getting this mechanic I found to do the work?

 

Yes. "Japanese engine with low miles," he says.

Hollywood, Florida - 3625 Pembroke Road, 33021
Ish Hybrids website
954.801.5434 (M)

"Yes I do everything on these cars," he said, when I sent him your questions.

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So, any ideas on accessing the blend door? It's been a few years since I took a dash apart - and that was to get to the display on a Gen 2. Any ideas on where I go to see how to get to the blend door actuator?

Or, should I even be looking at the blend door? It occurs to me that it could be a sensor issue, as well. My climate control display currently reads "outside - 73," although the weather channel says it's 80. Still, if I set it to "MAX," that shouldn't even matter, should it? I think it's gotta be the blend door.