Hot Exhaust Manifolds and water out of exhaust too hot to touch - GT40 Pro Boss

[edag]

Pulled my 1995 Nautique Super Sport out of storage from the winter. Changed the oil, tranny and V-drive fluids. Started it up in the driveway, hose attached. Exhaust manifolds are piping hot, almost too hot to touch and the water coming out of the exhaust is too hot to touch. This is all after a few minutes of idling in the driveway. Engine is PCM Pro-Boss GT-40 Multiport EFI 5.8L 310hp 700 hours. I am new to boat mechanics so I'm looking for some thoughts. Impeller? Thermostat? Water pump? Appreciate the feedback.

[Fgroce]

I would install a new impeller and stick to the oem brand. If the old impeller is chewed up, take off the cover where the hoses connect above the thermostat. Make sure no rubber impeller parts at blocking the passages. You will need a new gasket and may want to replace the thermostat or at least test it in hot water.

[surroundsound64]

Is this at idle or are you running it up? A typical garden hose can't supply enough water. You can rev it a little but not sustained. If you're running it above idle for longer periods I could see it getting too hot to touch. What does your temp gauge read? Should ideally be 140. Maybe at hot as 160-170.

[rpaldrich]

Have you had any exhaust work done? The direction of the manifold to riser gasket matters. If not, when was the last time you changed the impeller? If it's been awhile then change that and ensure you aren't missing pieces. You can also try disconnecting the intake hose prior to the water strainer, and use a long piece of water hose in a bucket to allow the engine to suck as much water as it needs. Fill the bucket with the hose, and this will most closely simulate on the water conditions. If your manifolds are still too hot, then look at replacing the thermostat and gasket-available at NAPA for a whopping 7 bucks. 160º thermostat for EFI engines. Bring the old gasket/thermo so they can match and while you have it all apart look for any missing pieces of impeller. Good luck!

[edag]

thanks for the advice. I changed the impeller and that seemed to help. I think I am going to change the thermostat as well. I took it out on the lake today and the temp gauge was about 160-180ish. also, there is a slow drip after installing a new impeller. obviously it didn't seal properly. I guess I will take it apart and try some silicone gasket. thank you for all the advice. its much appreciated.