1994 Mercury 40HP 2 stroke outboard overheating

[ROBJABLONSK]

I've replaced my water pump twice and engine is still overheating. I get tons of smoke/steam out of the pee hole and when I shut down the engine it puffs out a huge cloud of steam/smoke. See photo. I suspect the exhaust plate gasket is damaged right where the copper tube slips into it's home, the sleeve at the base of the exhaust plate. I do get a little water out the pee hole when I start the engine and run at low RPM's. But if i run at a decent speed, it turns to a spray of fine mist, probably steam.

I do not have any leakage from the power head. It is dry and solid and looks like new.

To test the water flow through the powerhead i connected a garden hose to the copper tube with clear tube and hose clamps. I turned the water on low flow and I get tons of water coming back at me down through the cavity in the mid section where the exhaust tube and drive shaft are housed. I also get water coming directly down through the exhaust tube. See pictures. Eventually a stream of water starts to come out of the pee hole. However most of the water is coming back at me down through the cavity in the mid section of the outboard and exhaust tube. Seems like the water is leaking back from the exhaust plate into the exhaust tube and the drive shaft cavity. Which would mean the gasket on the exhaust plate is bad?

 

[racerone]

??-----Most of the water comes down and out with the exhaust.----That is the way it works !

 

[ROBJABLONSK]

??-----Most of the water comes down and out with the exhaust.----That is the way it works !

Thanks for your help.

So water pouring down the exhaust tube as in picture #6492 is normal? adding to that, the majority of the water flow is coming down the central cavity where the drive shaft is. I estimate 80% comes down the central cavity, 10-15% out through the exhaust tube and the rest out the pee hole.

If water can free flow directly out into the central cavity, how does it build up enough pressure to drive the water up into the powerhead cooling passages? does the entire central cavity get filled and then pressurize water into the head once filled?

Thanks for your help. Trying to understand it well so I can fix it once and for all!

 

[buddhapi]

I am having the same issue with a 1981 50hp Mercury. at idle there's water coming from the pee hole but it's very warm. at higher RPM's it's like the exhaust overpowers the water pressure and forces the water down the tube. I may start a post of my own if I don't see any response on yours

 

[ROBJABLONSK]

I am having the same issue with a 1981 50hp Mercury. at idle there's water coming from the pee hole but it's very warm. at higher RPM's it's like the exhaust overpowers the water pressure and forces the water down the tube. I may start a post of my own if I don't see any response on yours

Exactly same. I think it has to be the exhaust plate gasket. Water is blasting right from the copper pipe into the mid unit through the gasket. Who knows maybe the copper pipe housing or gasket is loose/bad. I bought the parts to replace all of it. Will do it when they arrive mid week. I’ll let you know if it works! Good luck Buddah.

 

[Faztbullet]

2 different motors....2 different cooling systems. Need to start your own thread buddhapi

 

[ROBJABLONSK]

2 different motors....2 different cooling systems. Need to start your own thread buddhapi

Hello Buddhapi. I found the issue and fixed my outboard yesterday. Where the copper pipe from the water pump inserts into the exhaust plate there into a small plastic fitting and grommet that has two screws that hold the fitting to the exhaust plate. The screws were loose and the gasket was mostly gone because the screws came loose. Probably vibrated loose over the years. See pictures.

So the cooling water was spraying directly out of this fitting and into the drive shaft cavity and never making it to the head. Surprised my boat was able to run for 2-3 years while this problem kept getting worse. But it is fixed now. Unfortunately I had to take the powerhead off to get at this fitting and replace the gasket. I used some gasket sealant on both sides and Loctite on the screws so hopefully it wont happen again. 130 dollars in parts for the gaskets, sealant and I replaced my water pump again so it is 100% good. It took 6 hours to fix what was a $2.00 gasket and loose screw problem!

Btw only use the Quicksilver water pump. It is high quality and comes with better seals and fitment. Sierra and the Chinese brands are all terrible. One that I used had the metal cup off center and it rubbed marks right into the drive shaft. Crap.

Hope you get yours fixed!

 

[racerone]

Metal cups in water pumps are all off center !

 

[ROBJABLONSK]

Metal cups in water pumps are all off center !

Not to the point where the metal flares up in the center because it is rubbing on the main shaft. Anyhow, let's just agree it was bad sir. So far your input has not been helpful at all.