I recently bought a 1991 3500 7.4L Dually. The truck overall seems to be in great condition. It starts and runs well but I am concerned with the temps that I am seeing. At first it would run extremely cool, as in 160 degrees or so and it varied greatly depending on my driving speed. However, at idle the temps would start climbing and never stop so I would have to shut down once it crossed the mid-point on the temp gauge.

I checked the thermostat to see if it was there or stuck open. To my dismay, the thermostat was installed upside down AND it was stuck open (guess that was good in this case). So, I corrected that with a new and properly installed thermostat. Now, the truck reaches around the mid-point on the temp gauge but it creeps over the mid point at idle and even at driving speed. It makes me nervous because when I open the hood it feels extremely hot under there. I cannot touch almost anything under the hood because every surface seems extremely hot. I also noticed that my oil pressure starts dropping to around 25 to 30 when it is at these temperatures. My instinct tells me that it is too hot and that the oil is breaking down and losing viscosity.

I am just not sure what to think and it makes me nervous. I am about to go down the rabbit hole replacing things just to make sure that it is able to cool the best it can. I already did the thermostat. The next thing I have ordered is a fan clutch from NAPA. If it still seems excessively hot, then next will be a water pump and then finally a radiator. I figure at 30 years of age it won't hurt to replace any and all of these things.

My interest is in others experience and what running temps you are seeing with a stock setup in the early 4th gens. Especially with a 7.4L engine. There is so little information about the 7.4L in these early 4th gen trucks that I can find so I don't know truly what normal is. Does anyone have any experience to share?