I am having a very similar problem with my 240 that all started when i replaced the radiator hoses. I have not be able to improve it at all since. My car will warm my up in less than 2 minutes. It will run fine then all of the sudden temp just goes up to 115 or so then back down to 100 driving around town. I have noticed temp gauge is pretty erradic. It jumps around a bit sometimes pretty quickly. If i run on the highway for a while i can get it to 90 and it will stay there until i come back to stop and go traffic. Running heater will instantly drop temp to 85-90 but then it will climb back up. I've checked everything. I had the radiator rotted out and cleaned, i flushed the system and put new antifreeze in. Checked for air and doesnt seem to have any in the system. This all started when i changed my radiator hoses. It never once went above 85 degrees prior to that. Also, i have NO leaks. I'm stumped. Sorry for hijacking your thread btw.

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