1976 Mercury 20HP waterpump bad, engine overheated on muffs

[miichael18]

I have a 1976 mercury 20hp boat motor and it has been sitting for 2-3 years. i got it out today and hooked up muffs to it and flushed it out good and fired it up and it was peeing water. after about a minute i noticed it stopped peeing and i thought it was just my muffs not sealing good on the small unit. so i then took a barrel of water and placed the lower unit in and fired it up and i noticed just a few squirts of water then just steam and smoke coming out the pee tube. i have never noticed smoke and steam out the pee tube ever. i then shutr the motor down after about 2 - 3 minutes of running thinking the pee tube stopped up but the engine head was HOT to the touch. toree the lower unit off and every blade on water pump was missing due to dry rot.

Do you think the engine is hurt running it that long and getting it that hot? its not locked up and still hard to pull but i did notice steam and smoke out the plastic pee tube?

I ordered a new water pump impeller and gaskets but dont know what i should do to check the engine out to make sure its ok? worried me when i saw that steam and smoke out the pee tube. hope head gasket didnt blow causing that??

will a compression test tell me if the motor is ok? or what could i do to make sure head gasket or rings and stuff are ok?

It got VERY HOT when i touch the head it burned my hand i had to jerk back fast to keep from getting burnt.

any info or suggestions would be great.

 

[Jacket4life]

Re: 1976 Mercury 20HP waterpump bad, engine overheated on muffs

You're PROBABLY o.k., but here's what I'd do:

Check compression. If you don't know, it should be 130 psi. (perfect) but 110-120 is more likely at this age. variation of more than 10% among cylinders indicates a problem. While you have plugs out, check the tops of the pistons. If you see "bubbling", you have a serious problem. After that, I'd spray some straight oil into the cylinders after I check compression, assuming pistons look decent. Replace impeller, and fire her up.

This is why I ALWAYS run my motor with the cowling OFF when on muffs. That way I can rest my hand on the water jacket and ensure I'm not overheating. Really just don't trust the muffs, not how the motor was designed to run.

Best of Luck to you!

 

[miichael18]

Re: 1976 Mercury 20HP waterpump bad, engine overheated on muffs

so if my compression is good in both cylinders im fine? nothing else could have messed up? ill check compression tomorrow with both plugs out and see what i get.

 

[Jacket4life]

Re: 1976 Mercury 20HP waterpump bad, engine overheated on muffs

Well, other things MAY have gone wrong, but compression would be the worst one, since it would indicate a serious piston problem.

 

[miichael18]

Re: 1976 Mercury 20HP waterpump bad, engine overheated on muffs

Top cylinder was around 100 bottom was 105. thats on a pull start engine so it seems good to me?