ECT issue continue 1983 Chevy 20 Van w/ 6.2l Diesel pt.3

Those 6.2L diesels typically run cool when they are not under load. Remember they don't have an intake manifold dome filled with coolant like a gas V8 does. The valley on top of the engine is completely exposed to the ambient air. The air intake itself sits off the engine and gets very little warming from the engine heat so the engine will run cool in cold weather when it draws in cold air. When working alone you should be able to Rev up the engine up front by manually pushing in on the cruise control actuator on top of the engine. The thermostat housing is right on the front of the engine where it meets the upper radiator hose so access is easy. This time of year you should be using a 195 F thermostat. If your thermostat is sticking the engine will run hot under load I.e. while driving. Good luck 👍.

My vote would be thermostat as well. It shouldn't be too hard to get at. There is an aluminum crossover tube that goes between the two heads on the front of the motor with a bolt on thermostat neck that connects to the upper radiator hose. The thermostat is under the bolt on thermostat neck. That sensor you put back in the engine on the rear of the passenger side head looks like the temp sensor for the glow plug system. The temp sensor for the gauge should be in the drivers side head at the front of the engine. Both heads on these engine are symmetrical meaning it has exactly the same head for both drivers side and passenger side head, they Will exactly interchange. So the temp sensor for gauge is in the same hole on the drivers side just it will be on the front of the engine because the head has to be turned the other direction to fit in the drivers side. Hope this helps.

Is the car in the garage an Grand Prix GTP? I had in the past a Buick Regal GS 1997 with the 3800 Supercharge, it was a good performer. I love your 6.2, my father bought one in 1995 (A GMC Suburban) and kept it until 2004 and it was still running strong.

From page 2-53, THERMOSTAT The thermostat Figure 2-55 is placed in the coolant passage between the cylinder head and the top of the radiator. Its purpose is to close off this passage when the engine is cold so that coolant circulation is restricted. This allows the engine to reach normal operating temperature more rapidly. The thermostat is designed to open at a specific temperature (180 °F). When the engine is cold and the thermostat is closed and coolant recirculates thru the cylinder head and case. When the thermostat opens, the coolant circulates through the radiator. 1982 - Early 1983 Engines 180° 1983 and Later 190° Then also i see you must fill the resovair. DO NOT REMOVE RADIATOR CAP TO CHECK ENGINE COOLANT LEVEL; CHECK COOLANT VISUALLY AT THE SEE-THROUGH COOLANT RESERVOIR. COOLANT SHOULD BE ADDED ONLY TO THE RESERVOIR And have you charge the battery under floor, also tight alt belt. She is so lose.