1993 Mercruiser 4.3 Smoking from carb / blow by only at high rpm's and under load

[dlewis0714]

I have a 1993 Sea Ray with 4.3 Mercrusier. The boat has been running great all summer and the other day after I noticed the temp gauge got to about 180-190 after running it hard for 30 minutes straight so I drove around slow and it cooled right off. Next, I parked the boat went to get a bite to eat and came back got in boat and took off then it started to have power loss. I thought I got something in the fuel and I would check it after I got the boat out of the water. I got the boat out of water and took the plug and oil started coming out of stern. I investigated and noticed it looked like it was spraying out of dipstick and the top of motor. The motor is not making any funny noises and seems to be perfectly fine unless it's under load and gets to 3000 rpms and then smoke with oil starts pouring out of the breather tubes. I changed the oil and added marvel mystery oil and tried it again and still the same issue. There is no water in the oil and like I said with the muffs on I can rev 4500 RPMs and leave it there and its fine no blow by.

This boat sat for 10+ years and I replaced. Complete fuel system, all new ignition, starter, throttle cable, Rear main seal and crankshaft

 

[Bt Doctur]

I HAD a 1993 Sea Ray with 4.3 Mercrusier. The boat has been running great all summer and the other day after I noticed the temp gauge got to about 180-190 after running it hard for 30 minutes straight

Nothing like beating a dead boat with a large throttle stick.Oil mist out the dipstick is usually caused by excessive blow-by caused by a hole in a piston .or ripping the rings off a piston from detonation . #6 piston usually is the dead one so do a compression and leakdown test starting there.

 

[dlewis0714]

Nothing like beating a dead boat with a large throttle stick.Oil mist out the dipstick is usually caused by excessive blow-by caused by a hole in a piston .or ripping the rings off a piston from detonation . #6 piston usually is the dead one so do a compression and leakdown test starting there.

So if this was the case wouldnt I get blow by with the muffs hooked up in the driveway at high rpms?

 

[Bt Doctur]

There is no water in the oil and like I said with the muffs on I can rev 4500 RPMs and leave it there and its fine no blow by.

That has destroyed your impeller by now and will lead to a serious overheat condition and a no-load condition proves nothing . Do that on the water and let us know the results for the blow by

 

[dlewis0714]

That makes me think the temperature gauge is not working correctly because I have revved the boat like that before and it has never overheated out on the lake. I have seen the gauge get as far as 180-190 but that is barely over half way. If the gauge is bad I am sure I destroyed the motor and the boat is worthless IF not do you think it could be a lot of carbon gunked up in there? I was told to pull the plugs and spray sea foam and let it sit for awhile and try again and also put it in the heads....

 

[jrs_diesel]

There is no water in the oil and like I said with the muffs on I can rev 4500 RPMs and leave it there and its fine no blow by.

1500 RPM is the limit when running on a hose, any higher can cause the impeller to starve for water. I would definitely replace it.

No load blowby test proves nothing since there is nowhere near the combustion pressures as there are when running loaded.

 

[achris]

....and like I said with the muffs on I can rev 4500 RPMs and leave it there and its fine no blow by....

From the Owners' Handbook (you know, the one everyone throws in the rubbish bin without reading )





Now that you have thrashed your impeller, it's time to pull the drive off the boat, take it into you workshop/shed/garage, drain the oil and split the drive and replace all the burnt up parts. Also check the water pocket cover in the bottom of the upper housing. You've likely toasted that too.

Have a look at my videos for guideance on getting the drive off and on and servicing the water pump.

Chris.....