I have a 99 3.9l 4x4 Dakota. When I was deployed some guy at a parts store told my wife to run some stopleak though the coolent. Now the truck does not heat up. I heater in the truck is cool air, and the temp gauge is about 170. I used a heat gun to check the temp of the coolent hoses. Upper hose was a 140-150, lower coolant hose was 100-130. Heater core hoses were 150. Should I replace my thermostat? I know I should replace the heater core and I am about to start the long ordeal now. Any help or Ideas would be great help.....

 

170 is way too low, yes, change the thermostat.

You can try flushing the heater core first, or was the stop leak to fix it leaking?

 

No, the stopleak was for a coolent leak. But I think the heater core took to the stopleak better than the leak did... lol

 

Yeah, that's usually the case.

Still, it's worth a shot. When you change the thermostat backflush the heater core.

 

All stop leak stuff is crap dont use it most of that stuff will clog what you put it in its a bad idea.

 

Yes stop leak is meant as a emergency fix when your out on the road not a long term solution to a leaky rad. You will prob need to flush your whole system a couple times.