Replaced the clutch on the fan with no change. Only does this when I first start out, then it is fine (??) last night I took a different rout and it did it again when I was stopped at a light, but then immediately dropped to normal. Ghosts??

 

At this point other than the temp sensor, that is my only remaining guess unless you have some kind of blockage it is very wierd.

But to make sure I have things correct

• You startup
• Drive for while and the temps keeps going up almost to the top of the gauge
• Then it drops to normal and stays that way until the next start
• There are no other indications of an overheat such as lost coolant, or that very hot engine smell

 

Temp sensor was replaced, changed to a 180 thermostat, no change, then changed to a new 195 thermostat, and a new upper hose. When the truck sits overnight, When I open the coolant cap, it has a bit of pressure (new cap) so I don't believe it is a head gasket, r it wouldn't hold pressure.

when I first drive it, the temp goes up to 193. after a bit it starts going higher until it gets above 230 and then drops quickly and acts normal. vehicle has done this driving at 45, and at 65. same thing driving at 30-35 it doesn't seem to happen (??)

 

Ah but what are the RPMs, speed does not really matter so much as engine RPM.

But you have a D1 so pull the thermostat, now you will be running full coolant flow is it any better ?

 

I'll get some RPM readings changing from a 180 to a 195, the running temps at 55-0 mph were about 195-200 with the 180 stat, and 195 198 with the 195 stat.

 

Testing tonight, 63 degrees temp outside, as soon as I got on the highway and held RPMs at 2235, temp started to climb. As long as I held steady light pressure on the gas, temp kept climbing (same RPM) as soon as I backed off on the gas for a few seconds, temp started dropping even after I continued to accelerate to previous RPMs (2235) The rest of the time once temp dropped, it stayed constant at 199 temp for the rest of the drive. I am not one to mash on the throttle to get on the highway, just a steady acceleration with minimal RPMs to get the job done.

 

Well that matches what I see that underload in my D2, around those rpm's my temp will climb to about to 194-195 from 188 (180 thermostat). With the 195 thermostat 199 would be normal, I think, as far a running temp goes. It seem to me it is acting like you have an air pocket in there, once the air clears the thermostat everything works normally but I will admit that is a guess.

 

Thank you!

 

With variation of temp that wide and fast, air pocket is my best guess as well. Not always easy to get rid of them though.

 

I have tried running pass side up on a high curb, but that doesn't seem to work. I need to find a larger hill, maybe my neighbor's driveway approach as it is a bit steeper. Made sure everything was topped off and still the same thing on the way home tonight.. I'd think once the temp dropped back down, the bubble would be in the radiator or the coolant tank.