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Author Topic:   Merc 90 leaking oil in motorwell
Rich M posted 04-29-2004 11:53 PM ET (US)   Profile for Rich M   Send Email to Rich M  
This season I'm slipping my 2003 170 so the motor is in trailer tilt while moored. I've noticed when left for extended periods of time in full tilt I'm getting oil in the motor well. What causes this and is there a fix? Thanks in advance.

Rich M

jimh posted 04-30-2004 01:34 AM ET (US)     Profile for jimh  Send Email to jimh     
If the motor is a classic 2-stroke with carburetors, the oil you see in the splash well could be residue from fuel that drained from the carburetors as a result of the tilt angle on the motor. If you tilt the carburetors far enough, fuel may be leaking from the fuel bowls. This used to happen on an old 2-stroke Mercury I had.
RobTX posted 04-30-2004 08:12 AM ET (US)     Profile for RobTX  Send Email to RobTX     
Check the oil reservoir cap right after you tilt it up. My 2002 Mercury 90 2 stroke was leaking oil every time I trailered it tilted up, no matter how tightly I screwed down the cap with the O-ring. I ordered a new cap mailed to my house ($25, but less hassle than trailering it 30 miles to the dealer for their required "warranty part inspection") and the problem went away. On the other hand, I have also heard other people talk about the carb leaking a little oil tilted up, like Jimh says.

RonB posted 04-30-2004 10:26 AM ET (US)     Profile for RonB  Send Email to RonB     

I had the same scenario as RobTX with my 2003 Mercury 90 ELPTO on my 2003 170 Montauk. I had it in a marina slip with the motor tilted up and when I'd stop down at the marina I'd see a little greenish oil in the splashwell. After searching this site and seeing others with the same problem I put another 1/4 turn in the oil reservior cap and the problem went away. Although I now have a bigger Whaler I sometimes miss the performance and handling characteristics of that engine/hull combination.


Rich M posted 04-30-2004 11:20 AM ET (US)     Profile for Rich M  Send Email to Rich M     
Thanks for the replies. I should have specified that yes it is a 2 stroke. I'll try cranking the oil cap down more, if that doesn't work I'll order a new cap (still under warranty for a few months). I don't think it's coming from the carb because there is no fuel just oil. Thanks again.

Rich M

cmarques posted 04-30-2004 07:31 PM ET (US)     Profile for cmarques  Send Email to cmarques     
My 90 2 Stroke does the same on my Dauntless 160 if tilted too far up. Never worried about it, happens more if I fill the reservoir all the way to the top.


Jimm posted 04-30-2004 08:53 PM ET (US)     Profile for Jimm    
The oil cap can be too loose OR too tight!
John O posted 05-02-2004 12:55 AM ET (US)     Profile for John O    
Check the oil tank vent plug assembly. My new motor, 2001 Mercury 75hp 2 stroke did not have the vent plug assembly and leaked alot of oil when tilted at my slip.
Traveller posted 05-02-2004 04:54 PM ET (US)     Profile for Traveller  Send Email to Traveller     
I found a light greenish oily substance in my motor well and it turned out to be hydraulic steering fluid.
jimh posted 05-02-2004 05:10 PM ET (US)     Profile for jimh  Send Email to jimh     
If you've got the specified Teleflex fluid, it ain't green!
MantyMonty posted 05-02-2004 09:40 PM ET (US)     Profile for MantyMonty  Send Email to MantyMonty     
Rich, Noticed the same thing with my 90 in my slip last week. Just checked the cap and it is tight with no oil around the filler neck around the yellow fill cap. I'll have to take a closer look when I get it back in the water next week. Getting off of the subject a bit, do you have your Montauk barrier coated and bottom painted? I am planning on getting mine done this next week if the marina calls back this week.
1stwhaler posted 05-03-2004 11:51 PM ET (US)     Profile for 1stwhaler  Send Email to 1stwhaler     
my 90 two stokre has been leaking oil into motorwell since day one and it is not leaking from cap,one problem was vent cover on oil tank was not installed from factory but this did not solve problem,motorwell is always a mess.
Rich M posted 05-04-2004 10:30 AM ET (US)     Profile for Rich M  Send Email to Rich M     
Mantymonty - I'm in a freshwater slip with current and clean water. While I know there will still be growth I plan on cleaning it on a lift once a month. It's my first year in a slip so I thought I'd see how it goes, if I get staining or it becomes too much work to keep it clean I'll bottom paint next year.

Back to my original problem - I was wrong, there IS fuel leaking as well as oil. After 10 minutes or so it stops so I am relatively sure it is the carb bowls draining. My mechanic suggested disconnecting the fuel line and letting the boat idle until most of the fuel is cleared and then shut it off. I always did this with my old Johnson because I was told that fuel expansion in the carb could damage the diaphram. So I am used to doing this and think that it should solve the problem. Worth a try, I'll post back with results.

Rich M posted 05-05-2004 05:30 PM ET (US)     Profile for Rich M  Send Email to Rich M     
Problem solved. Pulling the fuel line did the trick. It takes a while, maybe 2 or 3 minutes of idle. Even then the motor never leaned out or showed any sign of actually running out of gas, but after shutting it down it didn't leak single drop when tilted. I plan on experimenting with idle time to find out the minimum needed to clear the carb bowl.
MantyMonty posted 05-05-2004 06:08 PM ET (US)     Profile for MantyMonty  Send Email to MantyMonty     
Way to go Rich, I'll try the same in a week or so.
sumnerdav posted 05-07-2004 04:55 PM ET (US)     Profile for sumnerdav  Send Email to sumnerdav     
I will try that also and if it works or not I'll report. It will be in the upper 80's here over the weekend!
sumnerdav posted 05-10-2004 12:04 PM ET (US)     Profile for sumnerdav  Send Email to sumnerdav     
I disconnected the fuel supply to the engine while it was running for a minute or two, prior to loading the boat on the trailer. No leaking was visible after the 50 mile trip back home. It was the first time that it did not leak. Thanks for the tip.

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