I have read a number of threads lately, mainly about thermostats and overheating but couldn’t find my answer. I own an 84 300SD that has been overheating. A few days ago when my wife was driving, it ran low on water and overheated. I replaced the water and inspected all hoses, none were leaking. When I noticed it was getting hot again I removed the thermostat to begin diagnosing the problem. I test drove it for about 5 min at 2000 rpm then about 10 min at 3000 rpm. After the 10 min piece, the temp began rising again and I inspected the system. The water in the plastic reservoir was bubbling (boiling) and was being forced out the overflow tube. I checked all hoses and they were all hot (both those attached to the reservoir and those on both sides of the thermostat connection). My first thought was the top hose from the reservoir to the radiator was restricted but I removed one side and blew air through. It passed through freely. I visually inspected the radiator from the front and the back and did not see any soil (dead bugs, dirt) sticking out. My next guess is maybe the water pump has quit turning but haven’t checked it out. Has anyone else experienced (and resolved) this or do these symptoms sound familiar?

Thanks,

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