4.3 Mercruiser Overheating

[BAproject]

I have a '91 Bayliner capri, 4.3l Merc, alpah 1 (gen 2) outdrive.

The engine is overheating, here's what I have done so far and can't track the problem....I really want to avoid just throwing money at parts that don't fix the problem.
Engine runs fine on muffs sitting in my driveway. runs fine trolling in the water, at WOT it gets up to 200 degrees quickly and then won't cool back down. ( i quickly shut the engine down and got towed back to shore)

Installed new exhaust risers 2 weeks ago
Installed new Circulating pump (old one had some play in the bearings)
New hoses
New belts

Have not replace the t-sat or impeller, I have read some things that lead me to believe its not the impeller if the engine runs well at idle(although it's been sitting for a while and is the "floppy vane" style impeller)....help please!

-BAproject

 

[Don S]

Re: 4.3 Mercruiser Overheating

The impeller is the FIRST thing to be checked in any marine overheat condition. Too many things can damage the impeller.

 

[BAproject]

Re: 4.3 Mercruiser Overheating

I was hoping you wouldn't say that I have done all the engine work thus far and resurrected her from a 6 year hiatus....I feel like I am so close but am almost afraid to drop the lower unit on the outdrive. I am guessing this is truley worth ti though!

I replaced the thermostat housing with a used one in better condition. Being lazy I used the t-stat that was in the housing. Also, I read in the manual that if I have a floppy vane impeller and a newer t-stat housing that I don't need to use the poppet balls that are currently in there. Has anyone heard of this, will it improve cooling without them?

-BAproject