6.5 non-turbo overheating with no load

[Thor]

I have a 6.5 non-turbo that was a replacement for a 6.2 diesel, it is in a 89 k2500. The truck temperature quickly reaches 200 whether it is 90 degrees or 40 below zero, outside air temperature does not affect it at all. I have replaced the thermostat several times and it does nothing. I want to know if my radiator might need to be recored, can I try a lower temp stat, or do I have to look at a performane water pump. I just want to know where to start so I am not replacing everything, when it might have been something similar. If I pull a skid steer for 2 miles it will be pushing 220 degrees in 50 degree weather, something is not right. Thanks

[gmctd]

The change from v-belts to serpentine belt occured right about that time - the water pump rotates counterclockwise for the serpentine setup.

Any chance a serpentine system got belts, or vice versa?

Fan and clutch?

[rjschoolcraft]

Also check the temperature gage. Hook up an aftermarket direct reading gage and compare to the stock gage.