I read an article by diesel giant about drilling holes in the thermostat to make the engine run cooler. I talked with my son again about his Peterbuilt truck with the same "run hot during warn-up cycle". He drilled a hole in the bypass thermostat and that fixed it. So, I drilled 2 3/16 in. holes in my thermostat and it worked. Yesterday afternoon and again this morning I drove the same route that has made it fail every time. Now it goes up to 185 +/- 2 deg and stays there.
I know that the MB design engineers know a lot more than I know. If something doesn't work correctly, fix it back to the way it was designed. Then I got to thinking, this car is almost 30 years old. The thermostats I have been putting in it are maybe only 1 year old. Not being able to buy a 30 year old thermostat, I may be forced to make what is available work. I know that there was a change in the thermostat housing in the 84 116 & 117 engine and another change in 86. So the 84 and 85 are different from the 81 to 83 and different from the 86 to 91. Why did they change them in 84 and again in 86 unless they had a problem? Why would they keep a thermostat in stock for 2 (116 & 117) engines only made for 2 years if something else will work almost as well? Give me your thoughts.

Paul

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84 500 SEL (307,xxx miles)