I just bought a 96 2500 and noticed that when the truck warms up it goes to 220 degrees or so and then all of a sudden the temp drops to 150. It does this more than a few times is this normal warm up procedure or do I have a t-stat problem. I also hear air bubbles in my heater core in when I first start it up. Im crossing my fingers and hoping its something easy and not something like a head gasket. The cummins has 250K on it so........ thanks in advance for any help

 

If I had to guess, and that's what I'm doing, I would say there is air trapped in your cooling system, and/or a stuck thermostat. I would look for a place in the system to purge air, if you can't find any vents, you could have a radiator shop pull a vaccum and then refill your system. Keep us posted.

 

I have a 95' Ram and I get the same sound in my heater core too. I have all new core, thermostat, and hoses. I think the noise is normal because the heater core "in and out" lines are slightly higher than the top of the radiator. My thermostat has a small vent on it as well.(looks like a small jiggly rivet). That piece must be on top when it is installed or else it takes forever for the system to bleed the air. The small gurgling when you fisrt start the truck, imo, is normal.

As for the temp, mine goes right to the center line (190) sometimes befor it cracks open. Going down to 150 is hard to achieve except for cold, cold days. And that would be a stat stuck open. (supercooling)


I would say your thermostat has reached the end of it's life expectancy, not failed mind you, just fatigued. Try changing it and see if your gauge displays normal operating temps after installation and filling. Let the air works itself out. I doesn't take long. If you still are not satisfied with the readings, change your coolant sensor, and make sure your fluid is acceptable as well. Bad coolant is bad because it has lost the properties that make it disipate heat. (sp?)

Good luck.