During the E36 M3 product cycle, BMW used plastic impeller water pumps. These plastic impellers would commonly fail from use, by either slipping off the shaft of the water pump (and no longer circulate fluid) as well as completely breaking off the shaft (on a whole, or in pieces). Failure can cause overheating of the motor. BMW continued to use these water pumps into the 1996 model production cycle (brownish color impeller).
Unfortunately, there is no way of determining which style water pump is installed in your E36 unless physically removing it. If you are not sure which style you have, it is an inexpensive part to purchase and replace. There are a few different ones available to use. The BMW P/N is 11-51 -7-527-799. Retail price is $79.95.
BTW, Bimmer magazine recomends the changing of said pump every 60K miles, but I find that a tad extreme.
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