Which thermostat should I use in my rebuilt standard Mk2 Cooper S?

There is not much choice. 82 or 75 are the main 2 sold for minis. You don't want the motor running too cold or you wont get the best performance. Start with an 82 and if your cooling system is playing the game it should keep the engine in the 90s. Some people also drill a 3mm hole in the outer ring if they are not running the water pump bypass hose. The old days thermostats used to have a jiggle pin in the outer ring to help get air out.

I’d go with the 82. You need it to be hot enough to burn off contaminates in the oil, and you also want it hot enough for the heater to work too

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