gt4turbo78
Recruit
- Joined
- Jan 12, 2009
- Messages
- 5
I recently purchased a used boat with a 1996 mercury 40hp 4cylinder motor on it. I added seafoam and tried taking it out and it ran fine. Took it out a few more times in the ocean and had no problems. Lower unit oil was clean. Peahole shot out water in idle strong and while moving. No excess smoke and no overheating. Flushed motor with freshwater everytime I came back. Ran 91 octane.
Then:
The last trip out the boat ran great all day but in the harbor on the way in while running in slow speed it started to smoke a bit. I thought it might have appeared that way because the sun went down but it was smoking for a good minute then the engine dies. Water was coming out of the peehole while smoking then the water stopped pouring out. A few seconds later the engine died. I popped the engine cover off and there was steam and the motor was hot. I let it cool for a few minutes till it stopped steaming then tried firing it up. It would not start unless I prime the bulb and excessively squeeze the bulb and rev. Then I can get it started for a few second and it will die again. The engine cranks but won't idle or stay running. I only attempted this a few times.
After:
After returning home I tried taking apart the carb (both of them). Seems to squirt fine with the float valve down, and tighten up when the float is up. No leaks or clogs in any of the fuel lines leading to the carbs.
Blew water through the peehole and there was no clog. Water came down the bottom just fine but I saw a leak in the valve cover gasket(?) where the spark plugs are. Took that cover off and saw that the gasket was no good and there was all this sand looking crud inside. I cleaned all that up and am planning to replace the gasket.
I removed the lower unit thinking that the impeller was bad causing the overheating. While lowering the lower unit for removal a piece of burnt plastic about 2" in diameter drops off. It came off around the top portion of the shaft or tube area. It dropped down from the top so I did not see where it exactly came from. The piece is just warped and melted so I have no idea what it is or where it came from. My guess was from the overheating the part that connects to the tube got melted? I took apart the impeller, and to my surprise it looked fine. No cracks and not hardened. I could not find a thermostat on this motor. Does it not have one?
In conclusion, I am absolutely baffled at what caused my motor to overheat. My assumption now is that the oil pump has failed but I have no idea how that mechanism works and it seems like a pain to get to. Can anyone help me identify my problem?
Then:
The last trip out the boat ran great all day but in the harbor on the way in while running in slow speed it started to smoke a bit. I thought it might have appeared that way because the sun went down but it was smoking for a good minute then the engine dies. Water was coming out of the peehole while smoking then the water stopped pouring out. A few seconds later the engine died. I popped the engine cover off and there was steam and the motor was hot. I let it cool for a few minutes till it stopped steaming then tried firing it up. It would not start unless I prime the bulb and excessively squeeze the bulb and rev. Then I can get it started for a few second and it will die again. The engine cranks but won't idle or stay running. I only attempted this a few times.
After:
After returning home I tried taking apart the carb (both of them). Seems to squirt fine with the float valve down, and tighten up when the float is up. No leaks or clogs in any of the fuel lines leading to the carbs.
Blew water through the peehole and there was no clog. Water came down the bottom just fine but I saw a leak in the valve cover gasket(?) where the spark plugs are. Took that cover off and saw that the gasket was no good and there was all this sand looking crud inside. I cleaned all that up and am planning to replace the gasket.
I removed the lower unit thinking that the impeller was bad causing the overheating. While lowering the lower unit for removal a piece of burnt plastic about 2" in diameter drops off. It came off around the top portion of the shaft or tube area. It dropped down from the top so I did not see where it exactly came from. The piece is just warped and melted so I have no idea what it is or where it came from. My guess was from the overheating the part that connects to the tube got melted? I took apart the impeller, and to my surprise it looked fine. No cracks and not hardened. I could not find a thermostat on this motor. Does it not have one?
In conclusion, I am absolutely baffled at what caused my motor to overheat. My assumption now is that the oil pump has failed but I have no idea how that mechanism works and it seems like a pain to get to. Can anyone help me identify my problem?