03CTDCO

Replaced my water pump and t-stat a few months ago. I haven't had the truck out on the road much since then. I typically drive 6 miles to work and back. Not enough to really heat up the truck much. The other day I took it out on the highway and noticed the temps were around 200-205 empty at highway speeds (65 mph). Noticed also that when I slowed down for a stop light the temps drop pretty quickly to 180. This is the opposite of what I'm use to. Could I have a bubble in the cooling system ? The coolant was changed (50/50 mix Zerex G-05) when the water pump and T-state was changed.
Any thoughts ? If its a bubble what is the best way to get the bubble out.
Thanks

IPDiesel

if it is a bubble, you could try removing the thermostat & bolting the flange back up.-drive down the road & the waterpump should be able to overcome the bubble with that restrictive valve in there.

I have also hear about a special valve located in the cooling circuit that allows air to escape but not coolant-someone else might know better-but if it does exist, yours might be buggered....

Dr.Dizzle

The third gens use jiggle pins. A thermostat can either have jiggle pin(s) or a calibrated bleed hole in order to purge the system of air during a service fill procedure and subsequent engine operation. I believe the factory Cummins thermostat is equipped with two jiggle pins. Many of the thermostats available in auto parts stores contain one jiggle pin or a bleed hole. I would describe jiggle pins as brass rivets located on the flange of the thermostat. Given the reasons you mention, I recommend the Cummins thermostat as replacements. The quality and robust nature of replacement parts at chain stores seems to be hit and miss anymore.

From the service manual.

REFILLING COOLING SYSTEM - 5.9L DIESEL ENGINE
Clean cooling system prior to refilling

1. Close radiator drain plug.

CAUTION: Due to the use of the one-way check valve, the engine must not be operating when refilling the
cooling system.

NOTE: The diesel engine is equipped with two one-way check valves (jiggle pins). The check valves are
used as a servicing feature and will vent air when the system is being filled. Water pressure (or flow) will
hold the valves closed.

2. Fill the cooling system with a 50/50 mixture of distilled water and antifreeze.
3. Fill coolant reserve/overflow tank to the FULL mark.
4. Start and operate engine until thermostat opens. Upper radiator hose should be warm to touch.
5. If necessary, add 50/50 water and antifreeze mixture to the coolant reserve/overflow tank to maintain coolant
level. This level should be between the ADD and FULL marks. The level in the reserve/overflow tank may drop
below the ADD mark after three or four warm-up and cool-down cycles.

Grey Wolf

There is a Allen pipe plug on the top of cylinder head towards the front that should be bled. Start it and open the plug slightly until the air stops coming out.

MikeyB

^Yep. Makes it a whole lot easier when refilling.

MikeyB