What am I missing? Heater still cold at idle w/fan on full.

I think this is just the nature of the beast. My heater air goes cool when the fan is on FULL and the RPM is around the idle speed of 600. It's toasty warm when driving or when the fan is on the first of second click. I noticed this 2 years ago but might have done it since new 10 years ago. Here's what I've done.

• Checked and replaced the thermostat. Both the old and new ones open and close at about 180 degrees using a thermometer and hot water in a pan. The old one wasn't defective but I replaced anyway. You can't install these backwards and I know which way they should go. The engine temp heats up perfect and quickly yet never overheats. Needle is at half way as it's always been in 105 degree weather or 0 degree weather.

• Flushed heater core both front and backwards using concentrated Prestone flush and then clean water, and then mild compressed air. I forced water through it both ways under pressure but was careful not to blow it out. I even measured the output of the coolant before entering the core and after exiting the core and both are the same with engine idling. (Bought a spare gallon of coolant to dump in at the same time as it came out). No clog and no yucky stuff coming out. I replace coolant every 50K miles with Toyota OEM fluid.

• I have zero air bubbles in the coolant. I got them out. I never lose coolant and the level is perfect and always the same. I even installed a bleeder at the highest hose just before entering the heater core. There are no bubbles in the system.

The water pump has metal fins and there is no leaking from the seals. I haven't replace it because I think it's good. It cools the engine just fine when idling for a long time in the summer and A/C is on. I never have even seen the temp gauge rise above half way while pulling a trailer up a 6% grade for 45 minutes with A/C on.

I have taken the engine cover off and traced all the hoses. None have kinks in them. Coolant flows into a clean bucket just fine as I've tested. (Now that I'm typing this I could try pulling the return hose just before reentering the block from the core and measuring the output). I just don't think there is an obstruction from block to the core and back to the block.

These trucks don't have a coolant shutoff valve before the core like many other vehicles have. Coolant runs through the core all the time at the same volume. It uses a damper inside to mix hot and cold air. I think driving with faster RPM vs. idle wouldn't affect the damper though.

What am I missing? This morning it was 17 degrees and while waiting at a long light I noticed it blowing cold air on my leg.

Thanks.

 

Just my opinion, have you tried "Recirc air" instead of having cold air coming in from outside? I live in Northeast and when winter, I usually never go above 2nd notch for fan and set air to floor vents and are usually toasty. If its real cold, I turn off outside air.

 

The heater core is just a radiator that exchanges heat into the cold air you push through it. You’re probably pushing too much air that is too cold and the heat exchanger can’t heat it up. Try turning the fan down to a lower setting and see what happens.

 

Had this issue with a pathfinder, ended up using a vacuum coolant machine. The core had a large air pocket in it.

the customer had done the diy drain and fill/flush. Didn't work quite right.

many of the newer vehicles(2005 up) have very tight cooling jacket tolerances and trap air in the corners. The air has to go somewhere, heater core is the path of least resistance.

 

I have had the same issue the last two years. Also have done everything knaryb has. This last weekend I ended up replacing the water pump for the heck of it, and of course no change.

I dig this vacuum idea, how do I go about doing that DIY? Or do you need special equipment for that? I have had the truck up at a steep incline and no air coming out the rad. I really do not want to go about replacing the core if I dont have too. So much to take apart to get to it. Lol.

Pretty sure this issue started after the stealership did my 90k mile maintenance and did the coolant flush for me. It was early summer two years ago though I never needed the heat until that winter so never noticed. Of course their solution was to flush again and I wasn't going to pay them for that.

 

the vac machine is something you can buy, but it is expensive. The shops have em.

you can try parking the truck on an incline...say 15 degrees or more and letting the vehicle run at that point till hot.

the machine pulls the coolant out via vacuum and creates a negative void than then draws the new coolant out of the fill side of the machine, all that’s left then is a up to temp run and top off.

 

Got ya. I have run it at an incline several times (ramps on an inclined driveway) after replacing the water pump this last weekend I ran the truck for like 45 minutes revving the engine occasionally up to 5k RPMs, engine was good and hot. Still no change though. I do think the vac idea is worth a shot though before replacing the core. I know that sucker isnt clogged I get full flow out of it when running a garden hose through it.

 

I hate to say it, but Firestone does have a special on coolant service... dunno if I would trust em... have not looked into a diy way of doing this. There has to be a wiki or something about building you own.
The pathfinder did end up getting a new water pump, it was only a part of the issue. DIY install with silicone... gummed up the thing, heater core had about a 1/16 of an inch in air at the top, did exactly what yours is doing.

 

This has been discussed here a number of times, but winters coming, so I'll throw it up again.

The easiest DIY way to bleed air from a cooling system is with a product made by Lisle. They make a lot of specialty tools for vehicles.

https://www.lislecorp.com/specialty-tools/spill-free-funnel-606

This gadget is available for sale from countless places(Amazon, ebay, some local parts stores). Lots of how-to videos on YT.

If you don't want to spring for this gadget, remove the radiator cap, top up the coolant and fit an old sock around the neck like you would fit a skull cap on to your head. You don't stuff the sock into the radiator. Set the interior heat setting to full hot - start vehicle - set fan on to whatever speed you like. The higher you set the fan, the sooner you'll feel hot air coming out the vents. If you're not feeling hot air after the engine warms up, you may have air in the system. Blip the throttle - crank up the rpms. Do this several times. This should help push the trapped air to the top. Warmer air should now start to come out the vents. Really stubborn air may require that you elevate the front of the truck(floor jack); then go through what I just mentioned. The sock helps keep the coolant from flying all over the place when you blip the throttle, but it's not perfect. You may get some down below. Clean up before the cat walks by.

I threw the sock away after I bought the Lisle gadget.

 

Yeah I am thinking of spending some time on Google and Youtube and then break down and have a shop do a vacuum job when I don't find anything. Lol Thanks for all the insight, new minds are always a help.

@
Lester Lugnut
I have that little guy, or at least the Autozone version of it anyways, and have used it several times. Had the front end up the truck up more than high enough to get that air out as well as had a more mechanically inclined buddy of mine do it also to make sure. Of course he was stumped of this issue and told me to take it back to the stealership for further diagnosis. Lol.

 

I had a similar problem where the heat would only work at high RPM's. At idle (stoplights), the air would blow cold. After checking to ensure no air bubbles, I took it to a local repair place. They diagnosed something (can't remember the terminology) plugged in the heater core. They cleaned/flushed and all was fine. Apparently, high RPM's meant high "flow" of coolant (?) but due to the restriction, idle RPM's would not push enough heat through this device? My apologies for not speaking the typical language of "guys who know what their car sh*t"

 

After doing all that work I would of said bad impeller on pump but replacement pump rules that out.
It has to be air bound. If all parts of system are good, has to be air trapped in system.
Impalas were know for this and a head gasket leak causing slow loss of coolant.
If your level is always good, its trapped air.

 

Well the water pump is belt driven so there’s that.

 

The coolant flush machines are about 500 to over 2k in price... the 500 dollar one is listed as a vacuum fluid pump, might only be for removal of oil, brake fluid, power steering...

the coolant ones are exchange machines...

 

My thought was the same, like the impeller was slipping or something. But you would think engine temp would reflect that issue as well. I don't think its a head gasket issue, no little bubbles seen with the rad cap open and off, no moisture in the oil or any of that jazz. Coolant levels are always good, never low, gotta be stubborn air stuck in there. I may just let some cleaner sit this weekend in the core and flush it again.

 

True that, I did look them up online, super expensive. Lol. Autozone needs to rent those bad boys out. Ha ha ha

 

Makes sense, I would assume when the dealership did the system flush you would think nothing would be left behind, but then again, it is the stealership. Lol. May be worth doing my own cleaning of the core at this point.

 

edited: I read the whole thread and I noticed no one has mentioned the different doors for the heater/vents. You might want to verify they're completely doing what they're supposed to be doing and not just moving partially. Maybe they're moving all of the way but a seal has fallen off. Good luck.

 

Isn’t t installed sideways tho?

 

Oh snap, idk, that would definitely create an air problem. I'm on vacation and don't have my truck to look at. Why would they... never mind lol.