OK guys im stumped. So I have a 77 nova with twin 302's in it. Fresh impellers and everything runs great at Idle. When I accelerate.... even on the hose..... temp goes up dramatically. I now what your all thinking. Thermostat right? Well took that out and problem repeated. After himing and hawing I decided to remove the risers and take a look inside. Passageways are unobstructed....even more baffled I sat down and noticed that there was a aluminum gasket the was on the manifold at the riser mounting location. looked a little closer and noticed that the gasket didn't have any passageway holes! it only has one small 1/8" hole in the forward passage way location. Is this possible a restricted gasket??? What for?? why would you need this? I''m clueless now. if you would like to see the gasket text me and all send it over 810-599-9607. I'm stumped, anyone got an idea? Thanks, JT

You never stated what the temp got to. Mine run about 140

hot! lol...190 anything after I shut it down

First off put a temp gun on the thermostat housing to see what you are really running.Keep in mind running on a hose is not enough water for higher rpm so probably want to keep it lower.If it just started doubt its the gasket a lot of risers have a restriction hole in one of the ports.How is the flow out of the exhaust?Do you have Bravos if so the first thing I would check is the pickup hose going to the transom assembly.Its right above the shaft and is usually a 11mm bolt.The clog quiet often.More so on boats that are not left in the water as air gets in there and corrodes it.

That actually is laser temp off the housing. As for the water flow it's good as good as the other motor. Looks strong. as for the gasket I know there are some restricted ones but this one has the 2 of the 3 completely blocked. That's just to odd... Also this is is a new boat to me so could have been an ongoing problem for previous owner. Pre alphas 888's

I think Mercruiser actually had a recall one the housing where the inlet hose attaches to the intermediate housing.
There is a plastic sleeve inside of the rubber hose, over time the corrosion builds up and slows down water flow.
You can run around at 2500 to 3000 rpms no problem but once you start pushing it the temp climbs. Post your findings.
Good Luck
Brian

Thanks for all the replys guys. Brian are you talking about the thermostat housing or part of the riser? Also still trying to find ou about this gasket and why you would ever use something so restrictive.

I was talking about specific part number 865470 baloon # 20 If you call up mercruiser parts .com bam marine bravo 1 outdrive, it shows a picture of it as housing . Where the hose connects to the gimbal housing. Not sure about your gasket question but I'm sure someone will respond to it.
Have a great day.
Brian

update....turns out the aluminum gaskets that were installed caused all the problems. Took them out and ran it with no thermostat and it barely broke 100 degrees at any speed. Still don't understand why they were installed in the first place. Ill just be happy I'm not going to have to replace manifolds and risers......yet lol. Thanks everyone who offered help!

Are you going to replace the thermostat? Running your engine @ 100 degrees will cause problems because it will never warm up to the correct operating temp.