Heater intermittently blowing cold air.

Hello,

I've searched around on this forum, and another forum, but didn't find exactly what I was looking for.

This all started last winter, and has been getting worse this winter.

While driving, the heat will cut out, and blow cold air. What I've been able to determine has some effect on this, lately, is engine speed. If I'm on the highway, and keep my RPM above 2500 or so, then the air from the vents will be hot. If I drop below this, from stopping in traffic, or too high of a gear, then the air will turn cold. If I return to higher RPM, then after a couple of minutes the air will turn warm again.

All the while, the temperature gauge indicates as appropriate. It'll reach the middle of the operating band a few miles from home, and stay there the entire time.

I just went out and drove several miles. On the way out, as the engine got warm, the heater blew warm air. I stopped, and felt both heater hoses. Both were warm to the touch. But due to that stopping, the entire way home, cold air blew from the vents. When I got home, and checked the hoses again, the top hose (as going through the firewall) felt warm as it had, while the lower hose felt cold.

I also felt both radiator hoses after I returned home, the top hose was hot, and the lower hose was warm. Based on my searches of the forums, I think that these are indicating normally.

I've already bought a new thermostat and gasket for it, but I'm not convinced that replacing them will solve the problem. It makes sense that the problem could be the heater valve, which would control the flow through the heater hoses and heater core. However, I haven't been able to locate anything that I'd call a 'remote operated valve'. Of the two heater hoses, one seems to attach to the lower block, and the other attaches to the head. The upper hose, to the head, might have had a wire connected near it, but it didn't seem to be loose, as I was hoping.

What else do I check? Is that the heater valve, mounted in the head? Is there another valve in the dash that would be the heater valve?

Thank you for any help.

James

 

sounds like you have air in the system. first id replace the radiator cap and make sure the overflow res is full to the mark. another trick is to park it uphill or on ramps when its cold and start and warm it up to burp any trapped air out. fill if needed

 

Thermostat.

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^^^^

 

Not knowing all the Tacoma systems, you didnt say what year this is. But, if it is a vacuum operated valve or vents then it could be a vacuum leak...if its a cable operated valve then thats either on or off as long as the valve is not corroded and locked up or broken, the cable could also be bent...the water flow is the next issue...I used to manage a radiator shop and worked on ac and heaters. Water should be hot going in and warm coming out just like the radiator-a heater is just a small radiator. I would guess if all else is correct then its a water flow or air in the system issue. Remove the rad cap when motor is cool. Run the motor till the thermostat opens and the motor and rad is hot. Then add fluid to be sure it is full. You may have to do it a couple of times to get the air out. If the thermostat was bad then the rad wouldnt be hot and the heater cool.

 

Thank you all for your responses.

My truck is a 2006, by the way.

I'm still hesitant to replace the thermostat. After I read your responses, this 'Similar Thread' was suggested at the bottom of the page: http://www.tacomaworld.com/forum/2nd-gen-tacomas/294003-heater-not-blowing-hot-air.html

It explains why I didn't find the heater control valve, and also suggests to get the air out of the system.

I peered inside the radiator cap earlier, and I couldn't see any coolant. The reservoir was empty, also. I have a bottle of coolant I'd bought for replacing the thermostat, so I'll fill the radiator and bottle first, and go through the paces for burping the system.

I'll give it a whirl this week, and report back with my findings.

Thanks again,

James

 

So far, filling the reservoir and radiator has produced remarkable results. I'd have saved myself a lot of cold rides if I maintained this truck better.

Thank you all.

James

 

I had the same issue. I had asked my mechanic check it out when I had my CV joints replaced. He didn’t look. Not sure how I lost fluid but I added fluid burped it and now it’s back to heating up like a stove.

 

As suggested, if your radiator cap is original, go ahead and replace it. OEM strongly recommended. Keep a close eye on coolant in the reservoir and make sure the level isn’t dropping over time. That coolant went somewhere, you’re going to need to track down what will likely be either a leak or a head gasket issue. Take a look at the oil to make sure it isn’t looking strangely milky, which would indicate the coolant is mixing with the oil. Do stop driving the truck if you see that.

 

This is a very old thread but none the less the Op's issues sounds like a plugged heater core as evidenced by one hot and one cold heater hose to the firewall. Options are to back flush it with clr and/or flip the heater hoses around and drive for a while. If no change then the heater core should be replaced

 

No, he was just low on coolant. For starters, it is a good idea to replace your radiator cap every few years. The OP didn't report back after January, 2015 so we will assume adding coolant took care of his problem (as stated by OP), and that he didn't have anything more serious going on.