Update on engine temperature readings.
Drove truck to a shop about 3 miles away. By the time I arrived, the temp gauge read H.
I had to wait about 30 mins to use the thermometer. We took initial readings - above the TS housing and below, radiator, upper/lower hose, front and back of engine. At that point the engine readings were 135 in the front and 140 in the back. Checked the temp gauge and it was at H. So, that tells me there is an issue with the sending unit or gauge.
Started the engine, revved it up to raise the temp. Focused on the TS housing and engine, we observed that at 181 degrees the TS opened and then the above and below temps on the housing read the same. The engine temp continued to increase, and the rear got up to 210 and stayed steady there. The front of the engine read 205. Had consistent temp readings on the hoses and radiator.
In summary, there is a 5 - 10-degree difference in temp between the front and rear of the engine. Interestingly, as I drove home the temp gauge started to move from H back to C but it only moved back a little and then went back to H.
So, I'll be doing some tests (or just replace) the sensor and gauge. I wanted to Thank everyone for your guidance and input, thank you Oz for staying on the thread. I am planning to rebuild or replace this engine in about a year or two. I will definitely make sure the heat riser valve is a part of that.
