1999 Ram 1500, 5.2, Auto, 2 wheel drive It takes forever to generate heat in the motor, I have replaced the thermostat twice 194 degrees, and I even have a big *** piece of cardboard in front of the rad, It takes about 20 miles on the highway before the gauge even starts to move. Once the gauge starts to climb then I have heat in the truck and everything is OK, It just takes so long to get heat. I wonder if the thermostat is not closing all the way? I can see one being defective but 2 in a week? Hey it's cold up here in Alberta...Jon

 

Check your fan clutch as well..... (although, given that you stated highway driving, even if the fan IS running, it wouldn't make much, if any at all, difference)

I used to buy thermostats three at a time, that way, I had some assurance that I would probably have one that worked..... Get a GOOD termo. The Stant Super Stat is a good choice.

 

I thought mine took awhile to heat up. I get about 4 miles from the house before the needle starts to move (that's about 8 minutes of city driving). When I have my grill inserts in during the coldest part of winter, that is cut about in half.