1994 dodge 2500 Cummings has never heated very well in cold weather 20 degree and colder.this engine has a small hose bypassing the thermostat could this be why I have little heat and why is it there to begin with.

 

Your thermostat could be stuck or non-existent. Unfortunately there are a lot of idiots who take out their thermostat to make the engine run cooler. This hurts performance and mileage.

 

have changed the thermo 3 times and even got one from the factory and had no change also block off the radiator at 20 degrees and colder

 

Can you post a pic of this bypass hose you speak of? I need to see where it goes.

 

the hose is right at the thermostat just below the income to thermostat and right above the thermostat the hose is about 3 inches long

 

Is it connected to a tube that runs toward the back of the engine? If so that is the heater line.

 

I have one of those thermostat housings as a spare and believe it is just to allow a little bit of warm water to bypass the T-stat before it opens so you can start to get a bit of heat.....so I highly doubt that is the reason for your problem.

Sounds like a problem I had many years ago on my 1st gen crewcab conversion. I was getting little to no heat, tried several different T-stats and the problem still persisted. I eventually figured out what the problem was.....turned out I had lost the vacuum source to the shut off valve on the heater hose inlet line to the HVAC box, it closes off the coolant flow when the A/C is turned on, so the AC works a little more efficiently. I hooked up the vacuum source and my heat started working like an oven again. So perhaps your shut off valve....is you have one on a 2nd Gen...is no longer functioning properly.

 

no the hose is just on the water jacket. ordered the truck new in 94 its a strait stick and has no air conditioning so would it still have the vacuum hose

 

Does the engine temp gauge run in the correct range? Is the engine getting warm, but no heat in the cab? Is this a recent problem or since the truck was new?

 

no the heat stays down around 145

 

It's possible the thermostat is defective. You can take it out and test it in a pan of hot water with a thermometer. It should be fully open at 195 deg. If it opens sooner then that's the source of your problem. With a lot of the parts now coming from China I'm always suspect that even new parts are mismarked or just plain crappy quality.

Edwin