FWIW . . . my 1991 242 w/ 454 (Mark IV) had a 143 degree thermostat, ran 150-155 all day long. Is this the original engine? Newer 454's went to the 160 thermostat. Match up your serial number on the engine to the proper thermostat. ( www.mercruiserparts.com )

Check to see what is in there and change accordingly. Also, make sure your cooling system is flowing properly. Check the oil cooler, sea water pump impeller, etc. If the exhaust manifolds are crudded up internally, that will prevent adequate flow. Also if the engine block has iron scale or sand in the water passages, that can make this run hotter. Lots to check with and older engine.

Another thing to consider, if all else check out, is that the temp gauge sender may have been replaced with one that is not quite compatible. That vintage Formula used the VDO series of gauges and senders.

The fact that the temp is consistent is a positive sign.

its the original motor with 600 hours. always fresh water. The fact it is so consistent i am assuming its a 160* stat.

KMoney did you pick up the 89 242 in Northern NY teal black and silver?

yes i did

other question someone might have a quick answer to. I notice the silent thunder platform has a small exhaust leak on the top. Only noticed cuz of a little soot and could barely feel it. I did a search and plenty of people talk about replacing the gasket but my question is will it cause any problem if i wait another month to fix it?

No problem when you take off the platform it may be gaskets or some soft wood not a big deal it happens to many of the older Formulas. It`s not a hard fix, post some pics of your new ride when you can.

Looked at that boat (was down the road from me) looked solid needed a little more than I wanted out of an 89 but think you have a good slate. Good luck

Cuposter. Just out of curiosity what do you mean it needed more than you wanted? This boat couldn't be any cleaner. Has a couple tiny tiny upholstery tears. Oh and could use a new stereo.. I gotta assume different boat. I looked at a lot of these and this took the cake.

K--Is this the boat? Think it is a good boat. Never really saw it used much, which showed. Great color scheme and 100% local freshwater boat. Owner was a really nice guy and glad it got sold to a good home.

Yup. Buffed it out this weekend looks great