Merc 500 cooling system

[jamiei]

With muffs on my merc 500 and the engine idling the other day, I had no water coming out of the pee hole. I flushed out the engine with these results... when i flushed from the top of the engine down, I had water coming out of the exhaust and not the water inlet tube. Is this normal? when I tried to squirt water up the inlet tube with the engine vertical, plenty of water went in but didn't make it out of the pee hole. When I put the engine up (horizontal), a little flow of water came out of the pee hole but not much. When I stopped squirting water up the inlet tube, about a quart or so of water flowed out of the tube. I'm replacing the impeller and suspect it could have caused the problem. Does anyone know if what I experienced is normal? I haven't ran the engine in a couple years and didn't want to take a chance on running it on the water to check this. Thanks for any help.

 

[12Footer]

Re: Merc 500 cooling system

The impeller should be changed every other season, whether it's bad or not. when an outboard sits for a long time (say a year or so), without being turned-over, the impeller vanes take the shape of the concentric housing. They also get brittle due to dry rot.<br />I would absolutely change this impeller. I would also pull the tstat, and after the impeller has been changed out, run it for a few minutes, just to flush the top end out. But be sure to put it back, as prolonged running without one can warp the head or the exaust port plates.<br />I would also remove the carbs ,clean them, and re-install before attempting to rely on it.

 

[tmcalavy]

Re: Merc 500 cooling system

What year Merc 500? My 74 doesn't have a thermostat, but don't know about newer ones. Sounds like your impeller is toast, or the critters plugged up the tell tale tube. Take a wire and run it down the tell-tale hole, carefully. Also try compressed air, you should get water out there when squirting water up the inlets. If not, you have some investigation to do. Once you get the impeller changed, it may be slow to pee at slow idle...until you boost the rpms a little. Mine does that at first, then whizzes like a racehorse.

 

[jamiei]

Re: Merc 500 cooling system

its a 69' with no thermostat and to clarify myself... when I was squirting water up into the intake tube, the engine was off and the lower unit was off. The impeller was still in good shape visually, but like I said i am changing it out anyway. Also, its not the tell tale thats the problem because I ran water into the tell tale tube and it came out the exhaust. None came out the inlet tube that I could tell is what puzzled me, but since the engine was off I didn't think that much of it. Also, I've heard a few people mention that water wouldn't pump up into the engine unless the lower unit was in a tank with water at or above the level of the impeller. Since mine only had muffs on it I thought that may be the cause. I did find that I was getting water in the lower unit lube via a big crack in the pump base so that problem is solved. I'm also planning on cleaning the carbs but it cranked up and ran really well for a 34 year old motor thats been sitting for nearly two years. I'm also rebuilding the fuel pump since the gaskets look pretty bad. Thanks guys