Cooling failed, now problems Mercury 500 50hp

[freedy1001]

Hi all, enjoying an awesome summer here in Australia, until last weekend.<br /><br />Motor is a 1977 Mercury 500, 50hp 4 cylinder.<br /><br />My water pump impeller failed whilst running at full throttle causing a big overheating problem. The engine suddenly lost power then stopped dead. I turned to see steam coming from the tell-tale and from under the engine cowling. So had to be towed back to the ramp.<br /><br />I got home and removed the lower unit and replaced the impeller, which was slipping on the shaft, hence the lack of water supply. Reassembled and fired up the motor. Ran okay with good water coming from the tell-tale outlet.<br /><br />However, there is water dripping out of around the #1 cylinder spark plug. Could this indicate a blown head gasket ? or possibly more serious damage. The engine sounds good, not rough.<br /><br />I guess a compression test will be the first item on the agenda. Or should I just go ahead and remove the head and take a look.<br /><br />I have never gone this far into a motor before, but have the manuals and some time over the summer holidays, so I'll give it a go.<br /><br />Many thanks for your time, freedy.

 

[andrewkafp]

Re: Cooling failed, now problems Mercury 500 50hp

Ahh... Another Aussie has found the No 1 boat site.... My $500 prize is getting closer <br />Do the comp test.. but the water is from the water cover and will not be entering the cylinders. I will link you to a few related posts. The "Slipping" on the impeller is delamination. Hope you have'nt done too much damage. DONT undo the head bolt unless you are prepared to remove that powerhead and do some re-drill-tap work.<br /> http://www.iboats.com/cgi-bin/ubb/ultimatebb.cgi?ubb=get_topic;f=29;t=015043#000013 <br /><br /> http://www.iboats.com/cgi-bin/ubb/ultimatebb.cgi?ubb=get_topic;f=29;t=014198#000002

 

[Laddies]

Re: Cooling failed, now problems Mercury 500 50hp

Before doing a compression ck on a over heated engine always add a little extra oil and run for a few minutes to let things free up before the ck

 

[emckelvy]

Re: Cooling failed, now problems Mercury 500 50hp

Definitely do a compression check. These motors don't tolerate a full overheating incident well. You very likely have fried a few pistons. #1 #2 will be especially suspect.<br /><br />The reason you've got water leaking from the cylinder block water jacket cover gasket is that when the motor overheated it fried that gasket. #1 cyl, being at the top of the motor, would of course be the hottest.<br /><br />So, the gasket got 'dried out' pretty good. At this point, probably not worth the trouble of tearing off the back cover as you're not going to see much. No cyl head to remove and see the piston tops.<br /><br />If you do find the compression to be down, might as well pull the powerhead and fix it right. You'll probably need a few pistons and a full set of rings, plus misc gaskets & seals.<br /><br />HTH and G'luck.............ed

 

[freedy1001]

Re: Cooling failed, now problems Mercury 500 50hp

Hi all, have not done comp test yet. Didn't have time to borrow the gear over Christmas, now away till mid January, so the boat has a rest for a few weeks.<br /><br />Anyway I did notice that there was a few fragments of gasket material protruding from a gap next to the #1 spark plug hole. This spark plug hole has a different surrounding cutout shape, like a keyhole shape to the left, whereas the other 3 are just plain round. This is where the gasket is showing and has left a small gap. I am guessing that this is where the steam was coming from under the engine cover when it cooked.<br /><br />So I sealed this area with epoxy weld and fired up the engine. No more water leak (apart from a small drop every 30 seconds at idle).<br /><br />Now wondering if this is the sum total damage ? I will still do a comp test to get an idea of the internals.<br /><br />Cheers,<br />Freedy.

 

[freedy1001]

Re: Cooling failed, now problems Mercury 500 50hp

I was just thinking back to the overheating event. What caused the engine to stop ? but then be able to start again okay some time later, and seemingly run smoothly now ?<br /><br />Freedy.

 

[andrewkafp]

Re: Cooling failed, now problems Mercury 500 50hp

The sudden stop was from everything expanding and lubrication burning off cylinders causing pistons to grind to a halt. When coooled, and re-started, everything has contracted and fresh oil is delivered to the cylinders. But the lack of oil can score the cylinders.If the compression is ok you may be lucky.