Heater blows cold at idle but warm when higher RPM's..??

I have a 2005 Toyota Tacoma 4.0L Double Cab. It blows cold air when at a stop light or at low speeds. It blows warm air when RPM's get around 2K or higher. I have checked the coolant level and is normal. The temp stays normal in not cold or hot. I also had the 100,000 mile flush and fill with BG back in August of 2013 and had no problems this last winter with heating.

I really don't want to take to Stealership for repairs and I'm quite capable of doing the work.

Now its going on winter 2014 and having this issue. My question is I have seen many things it may be like:

-Low coolant (which is fine)
-Some sort of bad switch or relay
-Heater core going bad
-Water pump going bad
-Thermostat (but seems fine as it warms to normal and stays normal)

Has anyone had this issue before and if so what was your remedy?
What steps should I take to find the problem and get it fixed?

TIA for any info and tips.

 

some sort of flap that gains the access to the heater core for the air to blow pass? i would say pop the glove box and start searching

can you rev the engine in neutral and have the same result that match the problem while driving?

 

Yes I can pop it in Neutral while stopped and rev the engine or hold the RPM's at about 2K and it will be warm again..

 

Is the blend door vacuum actuated on these trucks? A leak in a vacuum line may explain it.

It was ok after the flush, then got worse again?

 

The actuators are all electric, no vacuum control. Thinking outside the box though, I like it.

OP, are you checking the coolant level in the radiator, the overflow reservoir, or both? It sounds very much like an air pocket in the cooling system, which can happen for various reasons without the level in the overflow reservoir dropping.

 

Flushed and filled back in August 2013 was fine last winter (2013) no heating issues. Realized now with colder weather that it does not blow warm air at idle or stopped at stop light, sign, going through town at lower speeds etc...

Never really got "worse" just started not heating a low speeds or idle.

 

Coolant has stayed the same level for a few checks so far. Reservoir stays at same level and pull off radiator cap and its full as well. My next step is to try and "burp" they system and see if I can get any air out of it. I can also sometimes hear a "gurgle"or what sounds like water dripping or "sloshing" behind the dash of the truck when revving it to get heat. Kinda sounds like air is in the system but I have no clue why or how it got in there if it was fine a year ago...

I've read some other threads on the "sloshing" noise and hoping its not a head gasket letting air into the cooling system by compression...

The truck has NEVER gotten hot.... I'll start with purging or "burping" the cooling system and see what I come up with.

 

Tried the "burping" method and no air was evident in the system. I did check the heater core lines in/out and one was warm/hot and one was cool/cold. So I think I have blockage in my heater core. Going to try and flush that out and see what comes out of it and if it has good flow.

 

Just out of curiosity how do you unblock the heater core? I've been having very same thing happen on my 09. It was 29 in Texas the last few mornings and I need heat

 

My Tacoma has 2 hoses coming out of the Heater Core on the back end of the firewall in front of the driver side under the good. If its getting flow, the two hoses are suppose to be warm or hot. One is flowing into the heater core and one flowing out. I used a hose line clamp tool to keep fluid from running out of the hose when it has pressure (warm engine).

Took a garden hose and ran it on both lines a few times. Nothing ugly came out of mine. I imagine it has some sort of buildup that may need some CLR or cleaning agent to sit in it a bit and break it down. (Lots of videos online)
Be sure to get all the air out once its flushed or it will have air in your cooling system.

I did flush mine with straight water out of garden hose a few times and can now get better heat when at lower RPM's but still goes cold at idle.

When it warms up I think I'll just to a complete flush of the system with some LOW sudsing automatic dishwasher detergent (no lemon or scented just straight up detergent). Longtime shop owner buddy says this works better than the flushing fluid at most part stores. Just be sure to flush it with fresh water a couple times and you can get an idea of what comes out of it.

Saga continues for me....

 

I discovered the same issue this morning on my 05. It comes on the heels of noticing a 2nd gear stumble as well. Not sure if they are related. I did replace the plugs a few weeks back. Not sure if I bumped something or have a vacuum leak.

Looking forward to any updates from you.

 

Most likely the thermostat. I've had this happen to me before. It's stuck open and not letting the motor warm up completely. Worst case scenario if that doesn't fix it you've spent very little money and time.

 

I know that you've bled the cooling system, but some are stubborn.

With engine cold elevate the front of the truck as high as you can get it. Floor jack.

Pull radiator cap - make sure coolant is fairly full. Start truck - set heat control to max heat and let truck warm up. The elevation may push the trapped air out. If this happens, you'll begin to get heat after 10-20 mins.

If you have no heat by the time the temp gauge shows things to be warm - gun the engine. Put a sock around the radiator neck to keep coolant from flying all over the place. Do this a 3-4 times - pausing for a bit between each throttle blip.

If you have heat now - the air is out. Top up coolant - install radiator cap.

 

I noticed mine doing the same thing with the heater the last few mornings. But interestingly, I also experienced the "stumble", or "shudder", when backing out of my drive, then later when I was doing about 25 or 30. But I've also heard some belts squeaking (not squealing), when the humidity is up. So I've associated it with belt slippage. I may be wrong, but I'm wondering if I just need to get the belts replaced? I think it was 90,000 when I did it the last time, and I'm at 150,000 now. I live in southeast Texas, where the weather can go from one extreme to the other in just a matter of minutes, so the belts may be brittle or stiff due to weather variations and humidity.

 

Do you have the air recirculating on or off or does it not matter?

I have noticed that without the recirculate on when sitting at a light the air will not blow out as warm as when the truck is moving and its a pretty big temp difference. Not cold air but more like room temp air, then as soon as get moving again it warms back up.

 

Tried this method. Getting HOT air when gunning up to about 3-3500 RPM's as expected. When truck gets back down to idle it cools waaayyy down. Did this a few times after the trucks temp Guage read normal or in the middle of the temp Guage. Noticed lower radiator hose is nowhere near the temp of the upper radiator hose.

Going to replace thermostat tomorrow along with hoses as its all still original and 10 years old now. Think thermo may be stuck just enough to give it fits. Was researching thermostat prices online and read there may be a bleeder on it for air pockets. Anyone know about this or was it some marketing bull?

I'll update status if I finally get hot or still cooler air at idle when done.

 

I had a similar situation in my 05 a couple months back. I replaced the thermostat and got heat back.

 

This. Its your thermostat.

 

*Update* 29Jan2015

Replaced Thermostat with O.E.M from dealer along with new O.E.M radiator cap, upper and lower radiator hoses, and belt as it was still original and since I had it apart went ahead and replaced em...
Put it all back together filled with pink coolant 50/50 and jacked up the front end as far as the jack would go and let the engine warm up, revved up the engine a few times once warm to get all the air pockets out. (I used the Lisle funnel kit and it worked fantastic!!) We have had decent weather lately so today was the first day it has been cooler. STILL getting cooler heat at idle and at stop lights, signs...

Heater core hose going in gets hot but heater hose coming out is cooler/cold. I originally flushed out the heater core and it ran out just fine so I'm still at a loss as to what it could be. I would replace the heater core but it sounds like its a Pain in the arse, pulling the dash off....

If anyone has any further suggestions please list them and I will give it a try.

Thanks,

-Josh (Tacomajaybee)

 

man I am having the EXACT same thing right now---

did you ever get this issue repaired mr. jaybee?