No cabin heat

I have a 2016 Tacoma 96,000 km . The temperature gauge has been coming up to its normal position ,when up to normal position my heater is not putting out the heat it should, If I put the temperature to 22°C with the airflow set at low the heat seems to work better, if I turn the temperature up to 28°C the temperature seems to increase,but if I turn the fan To a higher speed the temperature of the air slowly cools off to cool. Also if I’m getting a good hot air coming out of the heater I can pull over and park in neutral and in two minutes the temperature of the air cools down . I brought the truck in to the Toyota dealer they fixed the problem I drove home with the heater working stopped and let truck idle for two minutes and it started blowing out cold air. The Toyota dealership says it is the thermostat. My comment to them is the temperature gauge seems to be working normal the temperature gauge rises slowly and stays at its normal position which is about is in the middle of the gauge .
Here is another example I’m driving down the highway temperature gauge is normal position I’m doing 110 km an hour for let’s say 15 minutes I pull into the parking lot and leave the truck running in neutral and within two minutes the Hot air turns to cold air. My truck was serviced with the total replacement of all the coolant at approximately 80,000 km also note my coolant level is showing full.

 

Thermostat

 

Heater core clogged? Heater core lines clogged?

 

Min

Mine (2017) did something very similar and my coolant was low, topped it off and heater worked fine..... now to figure out what happened to that coolant....

 

Just saw you said coolant level was good.... maybe an air bubble in the sys?

 

I don’t believe it’s an air bubble I’ve had this issue for 3 to 4 weeks and I’ve driven couple thousand kilometers.

 

I am leaning towards a plugged heater core and not a thermostat like the Toyota mechanic said I did have the vehicle in to get serviced and they did replace the coolant at about 80,000 km totally replaced

 

Thermostat doesn’t make much sense from your description, but temp gauges are usually highly inaccurate, you’d be better off using something like a scan gauge for better reading. But Many vehicles (every Toyota I’ve owned) have a bypass valve to the heater core. This valve allows engine to heat up quicker, and allows AC to blow colder. I have no idea if the 3rd gen has a heater core bypass valve or not, and if it does how it’s operated, (manual or audio), but that’s what I’d look for first. Ie sounds like coolant is not running through heater core. But If it was blocked or had air pocket, you’d never get heat, that’s why I ruled those out from your description.

 

Buy a cheap temp gun, and compare inlet to outlet temps. If it's clogged, you'll have hot in, and very little heat out,,,, of course depending on how clogged it is/may be.

 

My bet is air in system.

 

Thank you everybody for all your ideas and suggestions I will give you an update my 2016 Tacoma has been worked on by a Toyota dealership. The main issue is my heater puts out some heat when I’m driving when I stop at a stoplight the air temperature cools down when I accelerate and takeoff I get heat coming out of my heater. There are 96,000 km on my truck still under drivetrain warranty which is good my truck has been in the shop for a month. The coolant level is full no leaks no water in the oil no oil in the water, they have bled the air out of the coolant I would say a half a dozen times ,there is still air getting into my coolant so far Toyota has changed the thermostat change the water Pump taking the heads off , head gaskets were OK heads were sent in and tested ...Vacuum tested warp tested the only thing they did to the valves was lap the intake valves, so the heads were OK put everything back together still have the same issue air getting into the coolant it’s now been one month ToyotaMechanics do not know the problem ! Oh ! in the beginning my temperature gauge would raise from cold to a position of 12 o’clock on my temp gage which was normal since I bought the truck brand new now the temperature gauge is climbing above 12 o’clock and going up and almost touching the hot tick mark but has not gone into the red hot area of temp gage . Toyota has done a ton of things they are all still scratching their head as to why there is still air getting into my coolant example they flush the heater core they did lots of tests with heat guns pressure tested the radiator but the biggest job was taking the heads off having them inspected vacuum tested putting everything back together still having the same issue Air getting in to the coolant. Thank you

 

Probably the the blend door relay/ hvac system.
There was another member here that had the same issue.

 

Frustrating, but thanks for the update.
Unfortunately, they've dug deep enough to cause a leak, fixing another leak. They will have to find the leak to fix it right. Did they put dye in the coolant, still they can trace?

 

Yes they did the blue test . That’s what they call it .
Yes maybe another leak ?

 

Ambient air temperature sensor?

 

I have the same problem, but with manual heater controls, not the electronic climate control (17 Sport). I found that the temp gauge would go to the center position, then, if the heat came on, the gauge would immediately drop a small amount and slowly recover. I found that heat was always present as long as the the engine RPM was constantly above about 1700, below that the heat would begin to go away, and at idle never any heat (with a manual transmission I have full control over RPM). In warmer weather, (generally above freezing) the heat often works almost normally in that it was present at a lower engine rpm (but not generally at idle) and would begin as soon as the temperature gauge showed a reading. Coolant level is normal, has never been changed or added to. I have not gone to the dealer with this problem yet. Winter driving to keep the windows from fogging up is accomplished by keeping the windows open...

 

If your windows are fogging on the inside, that’s a good indication of a leaking heater core.

 

dye in the system and a pressure test should be all that is needed. The leak will show itself real quick when the system is pressurized.

 

Thermostat stuck open ??

 

OP, with all that testing .... was the heater core hot? If so the issue is in the HVAC system in the cab ...