overheating

[gypsyman]

Well, got pretty good use out of the boat this summer, and was just gearing up for the fall perch. But, am having trouble with the motor overheating. My motor is a MercCruiser i/o unit. Last week headed out to the water intake for perch, and didn't get much over a mile offshore, when it overheated and started to steam. Idled it back down to around 1000rpm, and got back to the marina, and the themp guage dropped back to normal. Mechanic at the marina suggested that the water pick up screen might be plugged with algea or zebra mussle's.
So raised the outdrive unit, scrubbed the screen off, and took a pick, as the mechanic suggested, and make sure the holes are clean. Went out into the lake, but not very far, and it overheated again. This time the temp guage stayed hot, so am wondering if maybe the thermostat might have went bad. The boat is 30 years old, and as far as I know, it's never been replaced. Any suggestions? Thanks-gypsyman

[quickdtoo]

Water pump impeller in the lower end needs to be replaced would be my guess. I've only had one I/O Merc which had a San Juan system on it, so I'm not real familiar with the lower end other than replacing the prop.

Tim

http://forums.iboats.com/showthread.php?t=273902

[gypsyman]

I had that replaced this spring before the boat went into the water. I will have it checked again thou, as I was told with the algea and zebra muscle's we have in Lake Erie, it might have gotten chewed up. It has a closed cooling system on it, and although it worked fine for several months, maybe the muscle's have closed down the water flow, so will have that checked too. gypsyman

[Rex in OTZ]

how does the discharge stream look?
On Alaska rivers Ive run into problems with smallish crumbs of crapola catching in the discharge passage on Yamaha motors we usally cleard it by rinning a bit of wire up the dischagre tube to clear the restriction.

[gypsyman]

Should have answered this last week. Pulled the boat out, and the mechanic hooked up a fresh water line from a hose. The stream coming out, could be stopped with your little finger. Hooked a pressure line up, and sure enough, the cooling system was plugged with zebra muscle's. Cleaned out the water pump, put new gaskets everwhere, checked out the impeller, and that was in good shape. Put it back in, and runs real good, and temp guage stays between 140 and 150.
Got it cured for this year, I'm wondering how I can prevent them little buggers from getting that bad. Don't know if the previous owner ever had any problems with them, as he didn't use the boat that much, and I really hate to pay somebody to do that, as it's something I can do myself, just don't have the time to work on it myself. gypsyman