have a friend that has a 97 4.3 efi with a bravo three out drive, water tempeture goes up to 185-190 then will drop back down to 120 then a few minutes later rises back up the 185-190 and then will drop back down to 120, this is after he replaced the seawater pump because of a bad impeller, he then replaced the circulating pump and thermostat, any ideas.
also does any one have a serpintine belt diagram for this motor to make sure he has the belt on properly.

thanks in advance
later

Somethings wrong in the t-stat housing or possibly the water flow. I had the same thing happening and ended up putting a new housing in; fixed it.

indeed that kind of fluctuation would seem to be thermostat based. good luck - jeff

I've seen similar problems caused by a bad head gasket. A quick check of the plugs will rule that out.

bad impeller, he then replaced the circulating pump and thermostat, any ideas.

Did you back flush the system to get all the little rubber impeller parts out? I am willing to bet that is your problem