Running Hotter than Usual at this Altitude

[Scootman]

Hello All,
Was wondering if I could a thought on something.
Just moved from Colorado at high altitude, 5280 ft above sea level. Have a 19 foot Bluewater open bow with the typical 4.3 mercruiser. The boat runs great, but when I kick that thing up to a high speed, above 30 MPH, the engine heats way above what I have seen in the past. As soon as I bring the engine back down, you can watch the temp needle come back down to normal almost immediately. I can run it all day at 20-27 MPH and not have a problem.
I have checked the in takes on the outdrive for obstructions and have always changed the oil regularly.
My thought is that the oil that was put in the boat in Colorado might be the wrong oil at this lower altitude.
Does anyone have any thoughts on this issue? Much appriciated!

[MikeyJ]

I'm not sure on the oil question, maybe someone else would know. However, if it idles OK but heats up when you are cruising maybe your impeller is missing a fin or two, or worn out. Have you replaced the impeller recently?

[Scootman]

Thanks Mike! No, the impeller has not been replaced at least during the time I have owned the boat, about 4 years and that may be exactly the issue. Never occured to me. Is this something that I can do myself do you know?

[MikeyJ]

No problem. I would start there, it is a good idea anyway esp after 4 years. It may not be pushing enough water to cool the motor when running at higher RPMs. I changed one in an outdrive a long long time ago but maybe someone on here would have some tips for you. It depends whether the impeller is in the outdrive or up near the motor how hard it is. I think that alpha's have the impeller in the outdrive while bravos have them up near the motor (but not sure on that one, as I said its been a while).

If you do end up changing it yourself, make sure to check the old impeller to see if any pieces broke off and if so, you need to find them in the housing or connected hoses so they aren't further along in the system causing partial blockages. Good luck!

[Scootman]

Awesome Mike! Thanks. One more question, I think I'll leave this one to the pros, any reccomendations for a good shop near Silkys in Sharpsburgh?

[MikeyJ]

I know fox chapel does repairs but have never taken my boat there. I am not sure about aspinwall, but they probably have the part. Would have to call to see if they do the service. Frank at Peggy's does a good job, not sure if he has a wait right now or not. I assume so. Hopefully others will have some more "reviews" on here

[SWIG]

I had the exact same problem on my 4.3v6 Alpha one Gen II last year that was driving me crazy. Would run cool all day putting around, but as soon as I would run fast enough to start to plane out it would instantly overheat. I had replaced the impeller and it did the same thing. I changed the thermostat on the motor, still was over heating. Finally, it turns out it also needed the water tube and seal in the outdrive. Once we put in that part it runs cool all day on plane. We think there was a leak in the tube or seal that as soon it got above the water line it would stop sucking water.

I would recommend replacing the impeller and the pickup tube and seal while you are pulling the lower unit to do the impeller. It is less than $20 in parts for the tube and seal, not sure about impeller price, but they are cheap and good preventative maintenance.

[Scootman]

Excellent advise! Thanks

[JZelt]

There is rt 8 marine (if you pull your boat out) or I think there is a mechanic at Millvale Marina. No experience with either.