If you look at my signature my truck is far from stock. I was going down the road and all of a sudden my temp Gage went to 240 and my heater quite. My first thought was head gasket. Then the temp would go back down to normal. I pulled over in a Covent spot and popped the hood no leaks no white smoke and the radiator over fill jug was at a normal level. But what I thought was strange was the radiator cap was cold. Truck did the same thing one more time before I got home.

The whole problem is the radiator was about 3/4 a gallon low on water. I have put about 500 miles on since filling the radiator and have had no problems. I have no leaks the reservoir jug is still on the full line. At this point I am not sure why water isn't going from the reservior to the radiator.
Just thought this info might interest some of you and prevent trouble down the road.

 

Need a new cap.

 

Yup, a bad cap that does not seal correctly will not create pressure to suck water into the radiator... Even though NAPA products are good, go straight to Cummins for a new cap. Should only be about $10.

 

Really a Radiator cap I can afford one of those

 

Yeah its nice when you find out it's a cheat fix!