Bad cooling on a 4 HP merc

[zodiaccaptianjj]

Hey, i have a 1970 4HP merc that has bad cooling.i just repaired a carberateur problem and got it running for the first time since the winter. I got it started and was running fine but i put my hand under the cooling water and it was burning hot, soon after the water turned into steam i let it run a little more and i wanted to see if it would cool down but it was still steam. So i shut it down and took off the cowling and every part insinde was burning hot especialy the cylinder case. I know how to do alot of repairs myself but now i am stumped. Im not really sure whats wrong. Im starting to get a little peeved. I hopeone of you guys can help me out.

 

[andrewkafp]

Re: Bad cooling on a 4 HP merc

Did you run it in a tank? Or in a lake ?<br />When you run these small motors in a tank, you must make sure that the leg is sufficiently submerged or air gets sucked in and the top cylinder is not cooled.<br />If it is getting some water, then it's most likely the water pump impeller. (Do a search on here, it wil be the most discussed of all posts).<br />If you have replaced the impeller, it could also be remnants of the old impeller floating around and blocking the cooling system.

 

[zodiaccaptianjj]

Re: Bad cooling on a 4 HP merc

yes i replaced the impeeler last summer and i had it running fine. and i also ran it in a tank and the leg was in deep.Now its overheating, could it be from the gas mixture or the spark plug heat? please let me know

 

[2loons]

Re: Bad cooling on a 4 HP merc

I agree with Unicorn on this one. I just did an impeller change on my 4.5 Merc (1975). I had the same symptoms you described. I't wont hurt to do a change out of that Impeller. Could be bad and you can eliminate the easy part first. Good luck.

 

[andrewkafp]

Re: Bad cooling on a 4 HP merc

The impeller should last for a couple of seasons, but if it is pumping hot water out,it's still kind of working.<br />Do a compression test on the motor, to make sure there are no piston/cyliner problems. When you removed the old impeller, did you remove it intact,or were there pieces missing ? The little broken pieces can get into the cooling system and restrict water supply. Although, this would probably reduce tale tale pressure significantly.

 

[zodiaccaptianjj]

Re: Bad cooling on a 4 HP merc

yes when i took the impeller out it was broken up. i am not sure if there are pieces in the cooling system. I did a compression test and it is showing good compression. If the cooling system is blocked how would i go about clearing it. does any one else have a opinion also thanks for replying everyone who did but i still need help to see whats wrong

 

[zodiaccaptianjj]

Re: Bad cooling on a 4 HP merc

also the tell tale has reduced water and its gettng so hot its pumping steam. but the impeller is brand new and there still is a proble i really have no clue whats wrong??