As the title says very little heat has been coming out of my vents. The guy i purchased my truck from says he replaced the waterpump. But it's about 18 degrees out living in northern new york. And took the car for about a 20 min drive and it doesn't get much higher then about 150 degrees. which i thought was way too low for the truck so i replaced the thermostat with no change. The truck gets much warmer when im driving at a higher rate of speed but when I slow down the car gets way cooler. Ive checked all the hoses on the engine and they are all hot, radiator is full. What else is there besides the heater core. And is there a way to check that too?? Thanks. Trucks a v6. 3.9 magnum engine. 1998, 5speed standard.

 

what thermostat did you put in it? 180 or 195?

If it is not reaching 160, you should be getting an engine light for "Engine too cold for too long". I forget the code #.

 

Garrett, welcome to the forum... I have the same problem, have 2 almost identical trucks,2000 Dakotas quad cab 4.7 4x4'sboth a/t, 1 had the heater core replaced by previous owner,has very little heat when moving,lots of cold air coming in somewhere. 2nd has great heat. I plan on checking them side by side to see if I can figure out heat.

 

Welcome to the forum Garrett.

It is possible to have a bad "new" thermostat. I'd definitely be looking at a 195 for where you live. If the heater inlet hose is hot and the outlet just a slight bit cooler and you have hot air, it's working normally. If one is hot/warm and the other cold, you've got a blockage. If in doubt, disconnect both hoses and flush it out.

The heater core should not make the engine run cold however.

Modlite:

Yours is probably easier to diagnose. There is a big foam seal (#24 on the attached PDF) where the HVAC ties into the cowl, a $12 part. It probably was damaged during the heater core replace (they do break down over time too.) When it fails, you have a cold air leak all the time. Also, aftermarket heater cores are smaller than OEM, you usually have to modify the housing some and fill up empty space with more foam.

 

Thanks Dan, how hard is it to remove the complete heater unit to be able to check all the seals & doors etc, ? also where can I buy the seal ? Bill

 

The seal would be a dealer item I'm sure. It's used on a lot of models besides the Dakota so it should be available. You would have to pull the dash and it's a lot of work. To remove the HVAC assembly to open it you have to discharge the a/c as well.

You might be able to figure out something else.

 

I bought a 195 thermostat. Someone recommended putting cardboard infront of the radiator and cutting a softball sized hole in it to keep air flowing in it. Anyone ever tried that??

 

Well ran a piece of cardboard over the radiator and not much of a difference but a slight one. (its negative 5 here right now) The temp. gauge fluctuated from 160-170 while driving to about 150 sitting at a light. The air gets a bit warmer when the rpms are about 2000 but cold when they drop below 1000. Anyone ever heard of this problem? Thanks again.

 

in your case, I think it's a matter of "It's too FFFFFing cold out!". With the clutch fan still moving air, the wind chill of the -5 air has to be -20 on the radiator.

Since you say it improves with coolant pressure, I'm going to guess that your heater core is probably plugged.

 

Their is a way to fix the air leak if its as 00DakDan says

I did this and it worked great

Remove your cowl its your air inlet at the windshield wipers you will need to remove the wipers then the cowl the pop rivets.

Now is the hard part I cut strips of Duct tape and hand placed them over the joint that is leaking the cold air into the cab.

Now this is not as easy as it sounds but WAY easier than removing your dash to do it.

The hard part is you will need to be a Contortionist to get them down and into the air vent its not easy to do.

You can feel the gap between the vent and the HVAC box and the seal if its gone because its a thick seal and if gone or rotted off you will feel that.

This Pic should help explain it