I have a 98 Ram 1500 5.9l. I have replaced the thermostat and heater core to try and fix my no heat problem. I still have barely any heat on cold days. Not even enough to keep the windows clear when there is more than just me in the truck.

The blower motor blows lots of air so I know it's working fine. Both of the hoses going to the heater core are HOT. The door on the passenger side to shut off the outdoor air works correctly, closes when on max A/C, opens on the other settings (vents, defog, etc). The selection door works fine and blows where it's set.

The truck's coolant comes up to temp like it should.

I don't know what else to do, we have a new born and he needs heat! If it was just me I wouldn't care that much.

 

Could a bad water pump cause low flow at idle? If I rev it to 2500 it blows much warmer air. The truck doesn't overheat or anything though.

 

Mine does exactly the same so I'm curious as to the responses to this.

 

go to autozone and have them test you rad cap... it maybe bad.... or just replace it... to rule that out of the pic... plus it may fix it

 

Has the air been all bled out? The heatercore can be a high point in the system and trap air?

If it blows hot air at higher rpms, then I would say that the water pump is potentially on its way out - or isn't putting out what it did from day 1. Combine that with an airlock in the heatercore? I dunno. Just thinking out loud here!

First things first, I would park it on an incline, or jack the front end up a good amount and start it with the rad cap off (COLD of course) and let it run a few minutes. As it warms up the air should be bled out of the system. Replace the rad cap and see if the heater hoses get hot (both).

In the meantime, you might want to do what I do... run the fan at a slower speed... the air coming out of your vents will be warmer as it has more time to warm up through a "cooler" heatercore.

Let us know how you make out...

 

The water pump could possibly have the impeller deteriorated or slipping.

 

Well the more I drive I notice the heat really doesn't get better when the RPMs are up. I will flush the shole system this weekend and also change the rad cap and put the front way up on the hoist to try and bleed the air out.

 

+2 on the radiator cap. I have been dealing with the same prob, so just for the heck of it I stopped at my parts store. They only had a brand new radiator pressure tester in stock, but I know the guy real good. So he opened it and we tested the cap. It would only go up to 12lbs then leak back down to 0. So got a new one and stuck it on. By the time I pulled out of the parking lot I had heat! YAY!!! LOL And just for info, every pound of pressure adds 3 degrees to the boiling point. So I was 12 degrees off which with these crappy gauges doesn't show up.

And btw it's around 22 degrees out. A balmy NH day! LOL

 

I threw a new radiator cap on and it didn't make any difference. I felt the hoses going to the heater core and they are not really that warm. The upper rad hose is hot, the lower is cold. That was after running the truck for 1/2 hour. It was fully up to temp.

Maybe the water pump after all? Truck has never overheated and I have most of the radiator blocked off with cardboard.

 

It also could have a plugged radiator core.