I have an 05 with Edge juice.No other mods.About 30000 miles ago I changed the water pump. I used a pump from the local parts house as I needed it right then. It has worked fine and still seems to work ok,I think!? The problem is the water temp. fluctuiates from 189-214 degrees per the edge monitor. The dash gauge moves around as well and mirrors them numbers as best I can tell. It does this when I leave from a stop light. At idle its around 194 and jumps to 200 when I take off under gentile acceleration,then settles back into around 192-198. Under a load it will jump to 214. The truck usally runs around 192-194,regardless of the load. The outside temp. is around 35-45 degrees.I traveled 600 miles with a trailer weighing around 4000 lbs.and the temp stayed steady at around 192-196.The belt appears to be in good shape. No squeeling from under the hood. What do you guys think the problem is. I would change the pump again with a genuine cummins if that will solve this. But dont want to find out thats not the problen hundreds of dollars later.The truck has always ran around 194 after it has warmed up,and never fluctuatied from that. The erratic temp changes happen fast too,it goes from 214 back to 189 in 10 seconds and back up before it settles in. Radiator and over flow are filled to the fill levels as well and has not been low. Thanks in advance.

 

Sounds like either a air pocket or the thermostat is going bad. Get a Cummins thermostat, they work best.

 

WARNING: DO NOT LOOSEN THE RADIATOR
DRAINCOCK WITH THE SYSTEM HOT AND PRESSURIZED.
SERIOUS BURNS FROM THE COOLANT
CAN OCCUR.
Do not waste reusable coolant. If the solution is clean,
drain the coolant into a clean container for reuse.
1. Disconnect the battery negative cables.
2. Drain cooling system until coolant level is below
thermostat (Refer to 7 - COOLING - STANDARD
PROCEDURE).
WARNING: CONSTANT TENSION HOSE CLAMPS
ARE USED ON MOST COOLING SYSTEM HOSES.
WHEN REMOVING OR INSTALLING, USE ONLY
TOOLS DESIGNED FOR SERVICING THIS TYPE OF
CLAMP, SUCH AS SPECIAL CLAMP TOOL (NUMBER
6094).
CAUTION: A number or letter is stamped into the
tongue of constant tension clamps. If replacement
is necessary, use only an original equipment
clamp with a matching number or letter.
3. Remove radiator hose clamp and hose from thermostat
housing (1).
4. Remove the three water outlet-to-cylinder head
bolts and remove the water outlet connector.
5. Clean the mating surfaces of the water outlet connector
and clean the thermostat seat groove at the
top of the thermostat housing.

1. Inspect thermostat seal for cuts or nicks. Replace if
damaged.
2. Install the thermostat into the groove in the top of
the cylinder head (2).
3. Install the thermostat housing (1) and bolts. Tighten
the bolts to 10 N·m (89 in. lbs.) torque.
4. Install the radiator upper hose and clamp.
5. Fill the cooling system with coolant (Refer to 7 -
COOLING - STANDARD PROCEDURE).
6. Connect the battery negative cables.
7. Start the engine and check for coolant leaks. Run
engine to check for proper thermostat operation.