Temp question? bad thermostats?

[540s10]

When I first start my truck and venture down the road empty with no load, the temp gauge will go up to 215 degrees, and then drop down to about 180 and then creep back up to 200 and stay there for as long as i drive it, and never go back to 215 until it sits overnight and i leave the next day.

it does this even on the highway so I think i've ruled out the fan clutch, as there should be more airflow goin 65 than the fan would produce, and being 15 degrees out its being cooled plenty.

anyone ever hear of a lazy thermostat that takes too long to open the first time, but then works fine after?

 

[bk95td]

Any thing other than a AC Delco or robertshaw thermostat will do that on a gm diesel

 

[matuva]

Check T-stats, verify there's no leak at your waterpump, good serpentine belt.
Get sure too the cap of the surge tank is OK

Consider doing the fun clutch mod

1st of all, make sure your rad is clean, especially between water rad and others.
And if your engine is running till several years with Dex-crap, flush the all thing and put regular cooler