Magical Mercury Mystery Rust

[avidda]

I have a 1995 200hp EFI Mercury. I run the engine about 10 times per year in the salt water in Louisiana. The boat is trailered and stored under a cover. The engine runs flawlessly. The problem that I am having is rust on the engine under the cowling. The spark plugs on the left side of the engine (facing rear of motor) have rusted. The lower sprark plug is the worst getting progressively worse up to the top. When I remove the plug the electrode looks fine, just the outer part of the plug that you use to screw it in is rusted. With the cowling off and the motor running at idle on the garden hose, I can see no water coming out out of anywhere. I have not revved the engine for fear of lack of cooling on the hose. I am thinking maybe head gasket or something, but wouldn't that leak at idle? As I said before the engine runs great. There is also some rust forming on some of the valve cover bolts and some of the other metal parts below the left valve cover. Any suggestion would be much appreciated. Can the engine run great with a blown gaset? And if so is it damaged nonetheless? <br /><br />dave

 

[Bob_VT]

Re: Magical Mercury Mystery Rust

Running a motor w/a hose does not stress the cooling system the same as WOT on the water. You might only have a slight leak and will have to find it on the water. Next time you luanch the boat keep checking the motor to see if any leaks appear. You might want to wd-40 the motor and components if they are going to be stored...that salt is real nasty stuff and it does not take but a few drops to start corrosion.<br /><br />Bob

 

[ruel42]

Re: Magical Mercury Mystery Rust

This is normal. I have twin 93's and the steering tube under the cowling and the powerhead support bracket under the bottom spark plugs are rusted from 9 years of running in salt. I have always flushed these and have also treated and painted the parts, but can't stop the rust. I also had a problem with the lower plugs rusting. This can be slowed by spraying the whole powerhead and spark plugs with a Corrosion inhibitor like CRC. What happens is the water gets into the lower area of the cowling and splashes on the spark plugs causing them to rust.

 

[avidda]

Re: Magical Mercury Mystery Rust

Thanks Knot enough, but it pains me to believe that a rusty motor is normal. maybe common, but i hope avoidable. The steering tube beneath the cowling on my motor is rusted for sure and i can understand that because it is constantly being dowsed with salt water, but inside of the cowling should be relatively water resistent since it does not get submerged so i tend to believe that i either have a leaky cowling or a blown water jacket gasket or something. <br /><br />all replies appreciated <br /><br />dave

 

[ruel42]

Re: Magical Mercury Mystery Rust

The next time you run it in the water take the cover off and look down into the lower cowling to see if the water that is in there is draining out. There are two small drain holes in the bottom corners in the rear of the lower cowling. If they are not draining fast enough this would hold extra water inside the cowel causing the salt water to spash onto the powerhead. Just a thought!!

 

[avidda]

Re: Magical Mercury Mystery Rust

I am taking the motor in for regular maintenance and will have them take a look at the rust.. I hope it is just a leaky or poor draining cowling..but I suspect some sort of blown gasket. I will post results<br /><br />thanks dave