I recently got the heater installed in my “Dord” and found I had no heat. The Cummins temperature sending unit, hooked to the Ford gauge never moved much off of the C on the gauge. I installed a “cardboard” thermostat in front of the radiator and was able to get the gauge to read about half way between the C and the NORMAL markings, (the gauge reads C \NORMAL/ H)and the heater to put out warm air. Yesterday I installed a Ford temp sending unit and removed the resistor that was in the Dodge harness where it attached to the sending unit. I drove the truck till it warmed up and the reading came up to the "R". Past experience with this truck tells me I had the temperature up in the 190 to 200* range. I installed a new 180* thermostat from Cummins, and removing my piece of cardboard from the front of the radiator I still have warm air from the heater and the temp reads at the bottom of NORMAL on the gauge.

Now for the questions.
After doing the above work, I have the top of the radiator hot to the touch, but the bottom is quite cool. I have never paid attention to this before, Is this normal?

Is 200* hot enough to damage the engine? I drove the truck 120 miles (about two hours) with the cardboard in front of the radiator.

 

On my Ford/Cummins, I used the Ford senders, right out of the old International.

I also had/have the original HUGE Ford diesel radiator, was old and now brand new exact replacement.

Before installing the engine, not knowing there was anything special, I installed a plain old 180* Stant thermostat.

I also have a mechanical temperature gauge.

No matter how long and hard I run the truck, heavy trailer or no, I have never seen the needle past 180*, ever.

It takes about three miles to get to 180*, it gets there and stays, no fluctuations.

At 180*, the factory gauge needle stays steady just at the leading edge of "N" for NORMAL.

I have plenty of heat, providing the shut-off valve is open.

The top of the radiator gets warm, maybe warm enough that you wouldn't want to keep your hand there long.

I have never thought to feel the bottom.

Which radiator are you using ??

 

I purchased a new sending unit from NAPA, which reads cooler than the one in my 460 gasser did. It should as the gasser had a 192* thermostat in it. I am using the Dodge radiator as I didn't have room to put my Ford radiator back in, the fan and the radiator would not have played well together. The Dodge radiator was half as thick, but quite a bit wider. I had to do some cutting and rebuilding on the radiator support to make it fit.

As far as a special thermostat, I was able to find my choice of thermostat temp ratings, I could have any thing I wanted as long as it was 180*. I called Cummins, NAPA and Dodge, they all told me the same thing.

 

Due to the design of the thermostat housing, a common mistake, and an easy one to make, is to install the thermostat backwards.

 

On a downflow radiator in cool weather, the bottom will be cool.

200 degrees is OK. 220 is where you should pull over.