No heat when idling. Help diagnose.

I remember the old road tractors, dump trucks & most all diesel trucks wouldn't heat while idling, exactly like this Tacoma is doing. Most had throttles so you could idle it up just a little & it would heat just fine. I drove an old "78" Peterbilt that had no throttle. I had a stick, cut to the right length, to put between the accelerator & the bottom of the dash to keep the RPM up just a couple hundred so the heat would work. Wondering if this normal problem with the old diesels would shed any light on this rare Tacoma problem?

 

FIXED!!!
Ok for what it's worth I had this issue on my 2013 that started out of the blue last winter. The heater just stopped blowing hot air when I stopped at a red light, then warmed up when I started driving again. So I took it to the dealership. They said they needed to hook it up to the diagnostic machine, which they did and told me my heater core needed to be replaced for like $2000. That sounded crazy so I asked him to just flush it, but he wouldn't. So I tried flushing it myself after reading this thread. I probably did it like 3 times or so. But I must have done it wrong because it didn't fix it. So then I take it to a mechanic and ask him to flush it. So he does, but it doesn't fix it, then he replaced the thermostat, nothing, then he decided to replace the radiator, nothing. that was all last winter. Well now i'm cold again and decided to take it back to the dealer and talk with someone else. I mentioned all the stuff I've been reading on this thread about blend doors and head gaskets, and whatever else. He said none of that would cause this issue and went ahead and did the flush. I made sure they did the back flush and everything else I've been reading. Ok, so long story short, and for whatever reason, this time it is fixed. The heat feels like a damn bonfire weather I'm idling or driving.
So if anyone is having this issue, maybe it's just a simple flush done right. He also mentioned that if you're using a hose to flush your system at home, and you're on a well as your water source, that well water is full of minerals and stuff that will clog the core, which is exactly what i did. so there's that also.

Good luck

 

So it may not actually have made any difference. That temperature difference could be the entire change.
Here's the thing about cooling systems; even when the thermostat is CLOSED, it still flows a bit. That could be enough to keep the system *cool* when ambient is that low. When you speed the engine up when driving, the amount of fluid flowing through the radiator will remain about the same until the engine actually warms up FULLY, BUT, the amount of heat that you are adding to it will be significantly greater. You've also got a 4.0, so aluminum block with a lot of surface area (you wouldn't believe how hard it is to warm up a SUBARU -- those boxers have about enough surface area to cool in the winter without a radiator!).

 

I tend to think you have a point. I hyper-analyzed every component of the cooling system and what I've come up with is that it's just the nature of the beast and normal for less heat at idle - especially if it's an A/T still in gear running like 600RPM. I even started the engine with a tube coming from the outlet of the heater core and timed how long drain 1 gallon of coolant. I then put the coolant back in and did it again at the inlet hose, totally bypassing the heater core and both were nearly identical. I don't have an issue with a clogged core, thermostat, trapped air bubble, radiator cap, low coolant, kinked hoses, or water pump output. I have an electric infrared surface temperature thermometer and my temps after driving for 1/2 hour with 30 degrees outside are: upper radiator hose 157, lower radiator hose, 71, heater core inlet 171, heater core outlet 116. This is while idling with heater on full hot and fan on full speed and waiting 1 minute before measuring. This week we had a morning that the outside temp was 16. I live about 4 miles to the freeway entrance and about a 500 foot drop in elevation. The truck does a lot of coasting and sitting at lights for the first 10 minutes. After driving 75 MPH on the freeway for 20 minutes and while sitting in my work parking lot it will cool down slightly if the fan is on high. It's unusual in a normal situation to be running a full fan after 30 of driving since the cabin would roast. At 3/4 or less fan it's hot after a full warm up. I'm not going to worry about it anymore.

 

We see a bunch of "lack of heat at idle" issues in the winter, all makes and models. The heater core passages are so restrictive, it doesn't take much to plug them up. A good back flush usually does the trick, if not it's heater core time.

 

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There is one thing you could try that may improve the situation; block airflow into the radiator. There are "grille covers" that you can buy, or you can make one. When you are approaching this as a solution, be aware that there are three air accesses into the radiator; the grille, the space in the middle of the bumper, and the space between the bumper and the splash pan.