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

Had the same symptoms on my son's 2007 Grand Cherokee...heard the sloshing noises and everything behind the dash just as described.

It was low on coolant. Fixed.

Paul

 

Love this site. This just fixed my heater!!!
seriously

 

Your heater core is partially plugged. Remove both hoses at the firewall and use a garden hose with an attachment on the end like what comes on a dehumidifier attachment hose and seal it to the hose, stick the attachment into each hole and flush the heater core out going in both directions. Have used this method many many times with customers vehicles, works like a charm...

 

That is a NEGATIVE.
The only thing I can think of left causing problems is either heater core or a weakening water pump.
I have read on here and other forums that some say the water pump gets weak and at higher RPM's it works fine but at idle it just doesn't have enough flow. Some also say there designed to either work fine or fail, so I don't really know which is correct.
Now the heater core sounds like it's going to be a real pain to get to and replace as it's stuck behind the dash and requires removal of dash. The manual recommends dealer to do it. Also read here that dealer is about $2-4k to do the job.

Soo, I have just been living with it. Honestly I'm thinking of trading it in for a Tundra or Sequoia as I could use a full size truck now days..

If any Toyota Mechanics read this and could shed some light on the water pump or heater core thing in the he mean time that would be appreciated.

 

Read post #10.......

 

Just flushing it won't help,, needs to be back flushed too

 

A plugged heater core is indicative of poor coolant maintenance. I change mine way more often than Toyota's recommended 100K interval and drain block/radiator + flush/back-flush heater core when I change coolant.

 

This was one of the first things I did was flush it both ways. It seemed to have great flow as the water shot out of each end when hose was attached.

 

Have you ever used any cleaning agents for the Heater Core to clean it out or just flushing both directions?

 

You dotn want to use any Chemicals anyway. They will rust your engine inside out. Stay away from those.
Looking at what you replaced, you are probably right that it could be WaterPump.
You sure its not head gasket issue right ?

 

I avoid these snake oil treatments. If you flush the core both ways during coolant change out, there will be no need for such products. Same for radiator flush.

 

Likely not a bad waterpump if the truck doesn't overheat. Sloshing sound behind the dash would indicate low coolant. Somehow you have gotten air in the system me thinks.

 

Has anyone fix this problem I am working on it my coolent level is fine my next step is a new thermostat

 

Water pump output is low. Either partially blocked line, or the impeller is slipping on the shaft.

 

I had the same issue, Every time I stopped at a red light or for something long enough that I was at idle the heat would turn cold. As soon as I would take off the heat would turn hot again. I spoke with my local mechanic and he said head gasket. I had the thermostat replaced at the dealer since that's what they said it was. The dealer was wrong and the local mechanic was correct. After the head gasket was replaced no more issues.

 

Mine is still worm just not as hot as when I'm going down the road.

 

Why would a head gasket caused this problem I've never heard of such a thing

 

I don't know why the Head Gasket Causes this to happen, But somehow it does.

 

OP, don't even think about going after the heater core at this point. Otherwise you will learn a lot of new words and see the neighbors rush their kids inside....

Did you reverse the inlet/outlet hoses to the heater core by any chance. Not sure it would make a difference though.

You said you burped the system. In addition, the factory manual wants you to grab and squeeze the large radiator inlet and outlet hoses. Did you do this? FWIW it made a difference on mine.

The bad head gasket thing is curious. I'm wondering if that cure was really due to having to drain, remove a bunch of stuff, and refill/burp the system as part of the procedure and maybe just coincidental?? IDK.

 

Check around your over flow bottle. If you see a white crusty material from where you have been boiling over that is a good sign that you have a Head Gasket issue. That was one of the signs my mechanic was looking for when he was ring to figure out my issue. Another is when you park your truck after a decent drive look or listen for your coolant to be boiling in the overflow bottle.