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Oil shooting out of dipstick

E

eneusiis

Regular Contributor
First I am going to apologize for posting this in the Honda forum, but its been months and no help in the mercury forum. I know JMGO or CHAWK may have a pretty good idea.

My hunting buddy has a Merc 25 HP 4 stroke, and was running it and lost top end RPM. No alarms, went back to the launch and oil was shooting out the dipstick. By the pictures he sent me....ALOT was coming out.

Is this caused by bad rings and blow by causing back pressure to build in the oil pan?

http://www.marineengine.com/boat-forum/showthread.php?449880-2008-F25ELHGAC-Symptom-help
 
Most oil pans will have a breather vent, which can get clogged up and cause what you described. I have no idea whether this engine has one or where it is.
 
Looks like that might be it. Usually they just take a good cleaning in gasoline or alcohol. Pull it and see what you've got.
 
Item 26 is the oil pick up screen, not a breather. Modern outboards have closed ventilation systems and its highly unlikely they will block up. Excessive crankcase pressure is usually caused by one or more broken compression rings.
 
I have to agree that the sudden power loss along with high crankcase pressure has me thinking your friend may have a serious problem in one or more cylinders. He really should do a compression test. I'm sorry to say I believe that he will find a low pressure hole on this one.
 
The plug may indicate some fouling but remember, even though compression is likely down considerably, it's probably enough that it's still firing off because it's pressurizing the crankcase. You may not see a big difference between the plugs when you pull them which, after all, needs to be done anyway to perform a compression test.
 
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