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Discussion Starter #1
Hi fellas,

I just got a '96 1500 4x4 (RED!). I bought it knowing the heat didn't work very well on it. Well, here's the problem:

When it's really cold out (say below 30 degrees (NOT 30 below 0)) the heat is almost non-functional. The guy I bought it off of said that he had flushed the core, replaced the t-stat and water pump already. Here's more detail on the symptoms.

If I leave the heat on low or medium it's nice and warm today (when it's +30 degrees, right now it's like 43 and it's pretty warm when I leave it on the floor on a medium fan speed). Whenever i put it on defrost it stays kinda cool, especially if I have it on high, then I might as well turn it off because there's no way it's defrosting anything. The thermostat seems to function correctly as I can see the temp gauge move when it opens. The guy said that he thought it was a problem with the HVAC unit. The blend door seems to move just fine because it will go from the "warm" that it does produce to cold and back just fine and I can hear it moving. Also the interior / exterior air door works fine too (I can see it through the glove box) but there are no changes in actual temperature by changing the settings to interior.

My opinion: Heater core because it operates better with lower fan speeds which kind of tells me that it's not getting GREAT flow but it's getting some.

Ideas anyone? Perhaps the blend door is moving over but not all the way?
 

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I would try to reverse flush it again.You could run some "clr" through it to help clean it out..
 

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Wow... not sure where to start. But I'll say this. Start from the beginning. Don't just assume the gauge is correct. The temp gauge on these truck is vague anyway. If you have access to a scantool, check the temp that way. That will show what the PCM sees as engine temp. Get a digital thermometer (one of the ones with a laser pointer preferred) and verify the engine is up to normal temp.

Make sure it gets to around it's hottest point (if a stock T-stat was installed... 192+ degrees) and make sure the coolant level is FULL on the overflow tank when warmed up. Add cooanlt if necessary, because the heater core sits slightly higher than the top of the block/heads. So if the engine/radiator is low, you'll lose heat. I would verify that I didn't have a leak somewhere by doing a coolant pressure test. If you have access to a tester, 16 lbs of pressure max. When I lost my heater core, pressure test didn't show a pressure drop, though, but after removing the glovebox door, I saw coolant on top of the HVAC box. I'd lose heat just like you described.

Once pressure check OK, and no leaks found, engine at normal temp @ driverside radiator tank/hose, coolant level good... then go to interior and look into mode/blend door operation. Sounds like (just a guess by what you spelled out here) that you're having a possible coolant issue, as opposed to HVAC problem. If it is a HVAC issue, may be vacuum @ control head or blend/mode motors?

Keep us informed what ever you find and Good Luck! :D
 

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Discussion Starter #4
Well, a few of the guys at work told me about this radiator shop down the road. I went there and when the guy said "$125 and you'll have heat, guaranteed or you don't pay" I jumped on it!

I've got heat now, but good! He said it took quite a while and a LOT of flushing but they got it done. Just the heater core needed to be flushed. Everything else was good. That's a lot better than replacing it... and it just seemed like far too good a chance to pass up!

Thanks for the help guys! The CLR idea sounded very promising... if all my hoses around the house weren't frozen. heh
 
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