Re: 1975 merc 85 head temp
WAY too hot!!!! Don't run it anymore until you find & fix the problem! That motor should be almost stone cold at idle, and maybe lukewarm or a tad warmer after running around for a while.
There's no thermostat on your Merc, so you've either got a shot impeller or some other circulation issue in the water supply tube or up in the powerhead.
When you pull the lower unit, blow air/run water up the copper supply tube & check for free flow. If you find an obstruction to flow, you'll need to start pulling water jacket covers and/or pull the powerhead for inspection. The cyl block cover (over the spark plug holes) is the most likely place for silt buildup in the block.
But, check the impeller first before tearing into things. It may be simple as a new one.
HTH & G'luck...........ed
