truck running hot with a load on

i have a 1999 k3500 6.5 turbo diesel i was towing a 1996 nissan maxima with the car trailer and temp hand starting rising how do you fix this problem thanks

Welcome aboard!

What is "starting rising"? Up to normal-high, or above normal-high? Was the fan roaring? Is it losing coolant?

If too hot, begin with normal cooling system maintenance items. Service includes fresh coolant and external cleaning of the cooling stack (radiator, evaporator, coolers), as well as periodic check and/or replacement of the thermostat(s) and fan clutch. If you aren't hearing the fan roaring when the temps rise, it could be either, or both that's failed. If you aren't aware of when they were replaced, now is a good time to start. A pressure test can help identify a head gasket or other leak failure.

hand got up too 250 the fan wasn't roaring or losing coolant

Assuming the gage is minimally accurate, then the fan clutch is the likely suspect. You can verify by checking the temp of the radiator at the time it gets hot. If it's above about 160F and the fan isn't engaging, the clutch is shot. If it's near cool to the touch, then the thermostat(s) aren't opening. The thermostat(s) should be replaced, in any case, either by themselves, or when the clutch is replaced. A cooling system test, and full service if due, should also be a part of this maintenance cycle.

Bought a fan clutch still going to 250 im replace the thermosts hopes this fix the problem some one put a electric fan on the radiator

Is the fan clutch now engaging? If not, then it's likely the thermostat(s) are not working as they should. The fan clutch won't work if hot coolant doesn't flow through the radiator.

Thermostats should be considered a routine maintenance item, and certainly replaced anytime the fan clutch is replaced. One is useless without the other. Also check the cooling stack for external fouling. It should be clean, through and through. Remove the top shroud and get a good look in between them. Repair/straighten bent fins as needed.

Electric fans on working vehicles are fine as a supplement, but should not be relied on as a replacement for the engine-driven fan. Often, they tend to be an obstruction more than a help. Generally, they are not needed or wanted, except during extended idling periods when A/C is needed. Even the best electric fans are capable of only a fraction of the capacity of the engine-driven fan, and when they aren't helping, they get in the way.

If it's really going to 250* you can expect their to be damage to the motor, when cold and you first crank the motor check the upper radiator hose, if it gets hard with pressure fast you have cracked heads or a blown gasket and it will be blowing bubbles in the coolant tank..

Blocked airflow through the radiator (and condenser and oil coolers) will make it run hot and prevent the fan clutch from engaging as well.

thanks for the info