Truck wont warm very much
 

My dad has a 2001 24v cummins. The truck used to warm up fine. Now it wont warm up much. It did it before we changed the thremastat. Thinking it was the thremastat but that didnt help at all. It was all of a sudden. Put a piece of cardboard covering the radiator and that helped some. It barely gets to 190 coming up a hill and wont go above 140 going down hill. No check engine light or anything. Any ideas what it can be? Thanks.

Try another t-stat. My truck will heat me right out of the cab even in -10 weather. Or try to flush the heater core. Take the hoses off and flush water backwards through the core.

Sorry I didnt make myself clear its not the heater its the engine tempature.

I've purchased new tstats before that were junk, try another one, and I think they sell premium ones too, well worth the money.

maybe see if you can put a mechanical guage in to make sure its not the gauge in the dash i had 2 pickups that did that to me before.

Just put a new engine thermostat in and you'll be all nice toasty warm again. They are real easy to change.

Not good to run these engines too cool. They work best and last a lot longer when they are run warm.

Cardboard over the radiator is not something I'd do.