No heat at idle - Heat gets warmer when above 1500 RPM

What?

 

There is an electric heating element that starts before the coolant gets warm, you can do a forum search for PTC heater.

 

That's cool, thanks for the info!

 

So Update 12/21
My closest appointment I could get was 12/23 8 am

however today I needed to drive to the post office which is about 7 miles away and about half way there its stop and go traffic.

First - Fired the truck up and let it run for about 30min
- popped the hood checked the coolant level and it is at the full mark in the res tank, also popped the cap when it was cold and the radiator was full
- hopped in the truck and it is ice cold heat settings as follows - fan 2 clicks on HI, on defrost and floor (I appreciate everyone's suggestions on settings to get the heat to work but either you actually don't own a tacoma or you don't know what the hell your talking about. Even talked to the shop foreman at the dealer ship and said there is no special way to heat the truck up... Put it on hi and dont be a dick and crank the fan to max... you think that would be common sense. I have warmed the truck up the same every year since brand new the same way heat on defrost and floor, on hi with a few clicks of fan speed and within 3-4 minutes truck temp is pipping hot.)

OK rant is over moving on

-looked at the dash gauges - Temp is in the middle right where it should be pop the hood one more time coolant level correct and Heater core hoses seem to be pretty warm

- I take off to the store. with in about 30 seconds of touching gas heat is hot again

- now I am keeping an eye on my temp gauge

- about 3/4's of the way to the post office (about 5miles) as I get into a little more stop and go traffic I notice the temp gauge starting to creep up over half with steady driving but nothing crazy...but its creeping

- go into the post office let the truck run just to see what it will do come back out and the temp gauge is right back middle

- take off and head for home now I'm noticing right off the bat temp gauge is climbing a lot faster and can notice a pattern. accelerating the temp drops ever so slightly back to almost where it should be, but then as increased steady driving occurs basically after accelerating to the speed limit the temp gauge starts climbing. Once I get to a stop then it really starts climbing it hasn't pegged yet but now its getting closer to the second to last mark where the "H" starts. This pattern seems to keep recurring slowly getting worse until I get home.

- I now pop the hood and check for some things like low coolant or leaks or hot heat coming from anything

Coolant is sill full, heater core lines still hot to the touch (still no heat at idle),
NO smell of antifreeze in the cab or it burning off the tail pipe. no leaks under the dash. So I let the truck idle a bit and it returns back to normal temp on the gauge...

Anxious to see what the dealer ship has to say. and really hoping that air somehow was introduced mysteriously into the system to start this whole mess... I've owned 34 vehicles to be exact from beaters to brand new and this bull shit is a first. I know I'm jumping the gun but if it is a cracked block or head or any other item like a heater core, Toyota can F off, especially that this truck has followed the recommended maintenance schedule since new to a T. It will be my last new one Ill ever buy.

 

If your temp Guage is actually moving, that's wild. I believe I had the truck up to 240* and it was barley moving. These trucks will definitely lie to you if you don't have the PID readout

 

Still sounds like air in the heater core.

 

I really hope your right!

If it is something stupid I'm still toying with the idea of pulling the trigger on a brand new one lol

Trading mine in with this crazy market

 

The VAG (VW-Audi) vehicles I have owned (too many) have a weakness in the heater cores. They tend to self block due to mineral build up and the fact that the "efficient" heat exchanger design tends toward small water passages. The use of "turbulators" to increase coolant flow agitation doesn't help.
I've needed to replace cores in both an A6 Allroad, and an A4. I tried chemical flushes, but once the passage is blocked , it;s blocked.

Perhaps Toyotas are similar IDK.

I suppose an infra-red imager could make any blockage of the core evident. I don't have a clue how to even get at the core except for just dismantling the glove box.

 

If the impeller slips on the shaft that would cause temps to rise as coolant is not moving. As temps rise, the hot coolant gets the impeller to swell and catches the shaft and starts moving coolant.

 

Because of the interference fit? That's a good point.

 

I’ve seen water pumps with impellers that are loose and with broken vanes.

 

Usually if water pump goes bad, it overheats or water boils through radiator into the overflow. Usually will see leakage or splatter somewhere under the hood. Needs a mechanic to run through it to be absolutely sure.

 

Depends on how it fails kinda.

 

Think about it

If the Water pump fails to circulate the HEATER core water, it also fails to circulate the ENGINE cooling water.

It would show on the engine coolant temp gauge on the dash

Lack of flow through the core is the reason, the cause is hard to diagnose without a through understanding of how it all works.

I might try a couple of " engine runs to red line" to push any air locks along. Then I would do a thorough inspection of the heater core. Might even take it out "just to be sure".

Any one know what a replacement OEM costs?

Autozone doesn't list a replacement for a 2020 4wd sport (selected at random)

ouch! what a PIA
https://www.tacomaworld.com/threads/heater-core.407504/

 

Tbh, I misread your post and was thinking about the seal failing and leaking through the weap hole. But even still, if the impeller is slipping on the shaft, it could be intermittent enough to throw one off. Air is still the most likely culprit imo though.

 

I've been fighting the same problem with my 2010 for 3 winters. You name it, I've done it.

• I've timed how long it takes for a gallon of coolant to go through the heater core vs. inlet hose into the heater core with the engine running. Both the same.
  
• I've back-flushed the core with air/water/coolant including an overnight soak in Prestone flush. Little to no particles come out in a clean white bucket.
  
• I've replaced the thermostat twice and tested them on the stove using a thermometer.
  
• I know I have zero air in the system since I installed a bleeder valve on the highest hose next to the firewall to going into the heater core. I lose no fluid over a year.
  
• I've put on 2 new OEM radiator caps.
  
• I replace the coolant every 50K miles.
  
• Pressure tested the coolant system.
  
• I have zero leaks anywhere on the truck.

Mine will go significantly cooler when fan is on high and the temperature outside is about 25 degrees or below. I can drive on the freeway for a half hour then it will get cool when waiting on the exit ramp for the traffic light. My temperature gauge never moves from a little less than half way. I never has any overheating issues on 100 degree summer days. I can't see how it can be anything except a water pump but with metal fins I don't understand how it can reduce volume if it still spins. I just live with it by moving the fan to low when stopped. I don't want to spend the time and money to replace the water pump when I'm not 100% sure that's it. I'm also a little scared to use CLR on the core due to it reacting with aluminum but I know many have done it.

I hope you can find the solution because I'll be watching. Good luck.

 

"engine runs to red line" will not push air out of a high spot in the cooling system -- You can't push a bubble down hill.

You can remove the uppermost heater hose with the (cold) engine running however and burp out the air.

Many vehicles use the heater loop as the bypass for circulation when the thermostat is closed. If the bypass won't flow as designed the thermostat doesn't see an accurate temperature and therefore can't respond correctly.

 

I like where your heads at! I hope that's what it is, I love my truck and the thought of buying a post covid/ manufacturing and quality slipping makes me want to keep my 16

 

Another thought:

On some vehicles the heater core has a valve on one of the heater core hoses to control the coolant flow; closed is cold, open is hot. Some of the valves are operated by a cable, an electric motor, or even vacuum.

On some vehicles the heater core is always hot, coolant is always flowing through. There are flaps that open and close off the air flow of the heater core into the HVAC box system. These flaps are operated by a cable, motor, vacuum.

What do our 3rd Gen trucks have?

 

Another good point. A while back I was asking about cleaning the coils of the core (to get rid of the musky smell) and someone posted the diagram of the box. I'll see if I can find it or if it has any info.