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Author Topic:   Two-Stroke Oil Leaks at Exhaust
kmiller posted 10-06-2005 03:33 PM ET (US)   Profile for kmiller   Send Email to kmiller  
I have a 2002 Mercury 90-HP two-stroke (90ELPTO). The last two times out I did not run the motor above an idle. When I store the boat at home I have the motor straight down to preserve room. There has been a small amount of oil leaking from the engine at exhaust. I have not pulled the cover and was hoping to know more of what to look for when I do.
Relatively new boat owner and am not sure if this is a normal occurance. This motor has less than 12 hrs of use.
No Respect posted 10-06-2005 05:11 PM ET (US)     Profile for No Respect  Send Email to No Respect     
If you were running at low idle for a long time and the oil is black or burned looking it may just be unburned two stroke oil coming out the exhaust after sitting. If the oil is clean or milky amber color then you have a seal problem that needs attention before you run it again. Good luck.
Buckda posted 10-06-2005 05:37 PM ET (US)     Profile for Buckda  Send Email to Buckda     
2-stroke engines tend to be leaky, smokey and sooty at the exhaust point, both above and below water. This is especially true when compared to the newer direct-injection 2-strokes (for Mercury, that would be OptiMax) and 4-strokes.

You may also experience a phenomenon commonly referred to as "spark-plug loading" when you are forced to idle for long periods/distances (i.e. when trolling). 2-stroke engines like to run at around 3,000 RPM. They don't really like to idle, and get poor fuel economy at idle. This is one of the strong selling points for 4-stroke engines among anglers - they can idle all day long and troll without loading the plugs.

I realize that it is not always possible, but if you can run the engine "at speed" for a while prior to trailering the boat, you may find that this "leak" goes away.

As many folks here who have boated with me can attest, the longer my Merc 150 idles, the smokier it gets. Let me run at speed and then slow back down, and she burns nice and clean.

Good luck.


boatboy posted 10-05-2005 01:40 PM ET (US)     Profile for boatboy  Send Email to boatboy     
If the oil is coming out of the exhaust outlet that's OK because it's a two-stroke but look closely to make sure and it not coming from the prop shaft seal or somewhere else in the gear case.
jimh posted 10-05-2005 02:00 PM ET (US)     Profile for jimh  Send Email to jimh     
A two stroke engine does not have an oil sump or reservoir in the engine. There may be an under-cowling oil tank which is not part of the engine. This could be leaking oil.

The lower unit gear case has an oil reservoir which could leak.

If you see this oil leak from the propeller shaft exhaust it could just be unburned exhaust residue which is slowly draining out.

davej14 posted 10-05-2005 08:31 PM ET (US)     Profile for davej14  Send Email to davej14     
I have a 75 2-stroke ELPTO which is basically the same configuration as your 90. In fact, I wish I had a 90 but that is another story.

You didn't specify where you are seeing oil. It is common to see a small amount of oil drip from the motor cover when the resevoir is full and I trailer in the up position. Even if I store the motor down (vertical) I will get a few drops in the motor well from the front of the motor cover. I usually just store it with a paper towel positioned under the drip to keep it off the gel coat. Not too scientific, but it works.

merc125 posted 10-05-2005 08:49 PM ET (US)     Profile for merc125  Send Email to merc125     
The plastic tank mounted to my 2000 125 elpto always leaked. It was replaced twice under warranty, but the leak always returned. When you tighten the cap to the tank it expands an O-ring in the neck of the tank. Over tighten it once, and it expands the plastic neck until the cap no longer seals. Leave your oil tank less than half full and the leak should stop. I sold that engine without resolving the problem. MartyD
jimh posted 10-07-2005 08:53 PM ET (US)     Profile for jimh  Send Email to jimh     
Storing the engine in the normal operating position is a good idea. It prevents problems with fuel leaking out of the carburetor float bowls due to being dipped at an angle. It is fairly common that some exhaust residue will drip from the propeller hub exhaust, but this varies from engine to engine. It will probably be more likely if the engine has been run at low speeds for a long time and there has been a build up of unburned fuel in the exhaust.
Gatored posted 07-07-2014 07:33 AM ET (US)     Profile for Gatored  Send Email to Gatored     

I found the perfect solution for a leaking 2 cycle oil container on my 1996 75 HP Mercury. I bought at Home Depot a 2 inch rubber PVC cap. It is made by Fernco It is a PQC-102. SKU 1857800049.

This is the real deal, remove the Mercury cap, place the rubber cap over the opening, tighten the clap with a screw driver, you will never have a leaking problem again. I fill the container to the top, tilt all the way forward and trailer across Florida with no leaks!!! Good luck. Hope this helps frustrated Whaler Owners like me!

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