5.0 Mercruiser Overheating

[OhioPaul]

I have a 1988 - 29' Stamas on Lake Erie with twin 5.0 Merc. I.O.'s. Last weekend when I took the boat out I was running at 3100 RPM when after about 5 miles I noticed that the starboard motor was running at almost 200 degrees. I pulled back the throttles and noticed that the gauge started to drop. I idled for about 1 mile and the temp came back to around 150. After fishing for a few hours, I ran back in at 2700 RPM. The motor climbed to 185 degrees. When I came into the harbor it dropped back to 150 by the time I got back to my dock. The outdrive impellers were replaced this spring. It appears that the thermostat is working. The boat has 585 hours on it and a good bit of those hours are from trolling. The belts seem to have proper tension and there are no obstructions at the water intake on the outdrive. Where should I start looking?

 

[Bt Doctur]

Re: 5.0 Mercruiser Overheating

Just the impellers or full kits.<br />places to look<br />water pump base housing/gasket<br />corroded water tube<br />collapsing water inlet hose from the drive to the transom housing<br />plugged power steering cooler<br />incorrect timing<br />lean fuel mixture<br />wrong plugs (too hot heat range)<br />circulating pump on engine<br />clogged riser/s

 

[Don S]

Re: 5.0 Mercruiser Overheating

Check the water pickup hose on drive side of the transom. When the hose gets old and hard, it can kink and restrict the water flow. Shells can also get stuck in the L shaped tube that goes through the transom shield.....right in the sharp part of the bend. But the first thing I would check would be the impeller, even if it was replaced in the spring.

 

[crazy charlie]

Re: 5.0 Mercruiser Overheating

While running motor with fresh water or in fresh water open the small brass drains on the risers and insert the end of a coat hanger and jab it around.See if you get black sediment crud out with the water flow each time you jab in there.If you do then just keep jabbing it as far as you can until the water flow runs clear.If you hit a dead end put a vise grip locking pliers on the coat hanger and hit the pliers with a hanner to force it in deeper to the riser.I had same problem years ago and corrected it with this "in a pinch" cleaning and unclogging method.Charlie