Tacoma loses heat below -10°C; thermostat changed, fan clutch issue

my 97 Tacoma stops putting out heat in the winter and temp gauge shows maybe quarter the way up. but this only happens once it gets to like 10 below Celsius, like right now no problem getting heat have to turn it down or it gets too warm in cab. and at current temps heat guage hits halfway and stays there. through middle of summer it didn't over heat once. so it keeps itself cool in summer but doesn't get to temp in winter. thermostat was changed not that long like last year, it was a 170 that was put in.

coolant is at proper level. ac was deleted (well belt removed) as compressor packed it in. i read somewhere about door in airbox getting stuck, is the same one that changes between heat and cold or is there another door between ac and non ac function? is it possible that clutch fan is not disengaging enough to not over cool engine in colder temperatures?

 

Does the truck sit outside? That is 14 degrees F, I'll bet the hoses to the heater core are freezing up. How far or long do you drive it when it's that temp?

 

that's after truck has sat there warming up for 10 or so minutes before heading out for work

 

14°F is nothing, a proper coolant mix won’t start to slush up until near -30°F.

 

True, But the only thing that turns off the heat is the heater core on/off switch on the firewall, not the blend doors. If it works until that temp something is freezing up somewhere. Wrong Aini-freeze mixture? The AC compressor has nothing to do with heat.

 

Unsure what normal is for your temp gauge needle since I don't own a first gen, but I'd suspect your temps are a bit low.

When an engine is struggling to reach temp, one possible issue is a stuck thermostat. I had an issue where my thermostat had an O-ring go bad and caused it to stick open in my 2008 GMC Canyon. The truck struggled getting up to temperature and even threw a code.

It could be worth replacing since they're usually pretty cheap and eventually need replacing anyway.

Edit: not sure why I missed that you already replaced it.

Did you purge your system of air? If you did, how did you do so? That can cause heating issues as well. The coolant reservoir (and sometimes the radiator) can all appear full but because of the air trapped in the system elsewhere, you can run into heating issues.

 

the work was done by the technician in the shop I work at. after replacing the thermo he used a vacuum system to create negative pressure in cooling system then draws coolant back into the system as the pressure is equalized again.

 

Don't quote me but I'm quite confident you have the incorrect thermostat. Most likely the correct temperature is a 185-190* thermostat. 170* sounds like too low a temperature to be opening up. It could simply be the wrong temperature thermostat

 

Wrong thermostat will definitely have an impact, if that's the case. (Especially if it's extra cold outside). It also sounds like the heat works other times, so it doesn't sound like a major issue with the system.

The other thing to consider is that idling vehicles don't warm up very quickly; you have to drive them to get them up to operating temp. The days of warming up before driving anywhere died with the carburetor.

 

What I recall is halfway would be normal on my wife's 1G Tacoma. I would think you are on to something with that @RedWings44

I'll second the thermostat, at least it's a cheap job and probably needing done soon anyway.

Never did one on my Tacoma but I recall long ago that most fuelie cars (so pretty much everything now) needed a 185 or so. We bought my parents a car that the stat had been removed..my having driven only old carbureted vehicles went to the parts store for a 170 stat and when I gave the vehicle specs they said it needs a 185 because fuel injection/computer crap to run right. I took the stat home, tossed it in, and 10 years of use after that proves the point.

 

OP, if you put a new TStat in use a factory TStat… yes they are pricey. You did not mention what motor you have, on the 3.4 install the Tstat with the jiggle valve at the 6 o'clock position on the 4 cylinders it goes at the 12 o'clock position.

 

I'm not familiar with that method, but that doesn't mean it is bad. One way to tell if you have air trapped in the system (aside from checking both the overflow and radiator) is if you only seem to get heat while driving or if you shut the vehicle down and sit in it for a bit and start hearing a liquid dripping/running sound from inside your dash.

As some others have mentioned, it sounds like your thermostat may be too cold for the proper operating temperature. I've also heard of thermostats being installed backwards causing issues.

 

This 100% sounds like a thermostat that is stuck open.

FWIW, a thermostat that is fully functioning but otherwise installed backwards would cause the engine to run hotter since the end that needs to be heated up to open will be on the side where lower temperature coolant is coming in from. It'll still operate (theoretically), it'll just make it run hotter since it will open way later due to the temp difference.

 

its halfway on the gauge where it runs all year except for in the winter especially when it's like -20C/-4F or colder.

 

Yeah, the gauge is not super accurate only because it takes a huge temperature change for the gauge to actually change where it's at. If you get a scangauge or some kind of OBDII reader you'd have a more accurate telling of what temp the engine coolant is at.

 

Oooh good catch, @Murd3rd

 

The fact that it would be showing low and not blowing hot would still indicate an issue.

 

I agree and tells me that it's more than likely the thermostat.

 

Or low coolant, but it seems we've dispelled that.

That said, a bad stat "could" mimic that effect if it's not letting the coolant circulate as it should. I'm leaning that way or perhaps a water pump issue if pressed.