Crankcase presure!

[Towboat1]

I have a 2001 F115 I used the boat last wek to fish for three days! everythinf seemed fine untill I got home and went to flush the engine. I hard a hard time starting it and when it started it ran rough! I changed the water seperater and filter on the side of the engine and went to check the oil!!! this is when I noticed I had a problem. When I pulled the dip stick out oil shot out like it was under presure, I drained the motoer oil and it seemed runny but not milky. Any assisatnce would be greatly appresheated !!! Thanks Mike

[robert graham]

Sounds like your motor is "making oil", a term used when fuel gets past the rings and into the crankcase, diluting the oil and adding to it's volume. Your prop and wide open RPM's are very important on that 4 stroke motor. Have you been doing a lot of low speed/*****ing? You need to run your motor at wide open throttle(5000-6000RPM's) for 20 or 30 minutes at the end of the day. This "making oil" has been an issue with some of the 4 stroke outboards.
Good Luck!

[Sparkieboat]

those motors like to be run at high 5K RPMs, 5800 or so. people who over prop and only get into the low 5Ks have problems. If you are getting pressure into your crank case, that is not good. I would search out a highly recommended Yamaha Master Tech, and have him take a look at it. They can be hard to find, but these EFI 4 stroke motors require a good deal of experience and knowledge to trouble shoot. most back yard guys would only screw it up.

[99yam40]

Check fuel pump for leaking into crankcase, check to make sure stats are operating properly(cold motor will cause rich running),do a leak down test to make sure cylinders are sealing properly, and make sure it is propped correctly.

run it hard to heat up oil and motor at the end of the day to cook off anything in oil

[Towboat1]

*** !!! I visit lots of forums for my truck ,4 wheelers , and dirt bikes but have never seen such a response as this site!!! THANKS!!! I was in fact *****ing for Strippers with my boat for four days at a slow ***** speed of 2.8 to3.0 . I ended the day with a short run back to the dock 15 min. at 5000 rpms. If I did run it to the point where it was filling the crankcase with feul have I damaged anything or am I safe to just change the oil and filter and be more aware of running the boat at high rpms after *****ing ?

[99yam40]

Change the oil and filter and make sure fuel pump is not dumping fuel into crankcase. Check oil level more often
Is 5K your WOT rpm?

Hard to say if anything was hurt from lack of lube due to diluted oil

[Towboat1]

I generaly do not exceed 5000rpm's ! but I thought that was a good idea ! guess I'll run the engine at 55 or 6000 when coming back in. I checked the fuel pump-no leaks, cly.compression -178 all four, replaced the thermostat, oil and filter ! started the motorand ran in off the garden hose for 15min's ! so far OK if it's not rainingtoday I'm takingthe boat out to run it. Thanksforall the assistance guy's

Mike

[99yam40]

WOT RPMs will tell you if it is propped properly

Leak down tests is a better test of cylinder sealing

[Towboat1]

I'm not sure what WOT means ! I can get almost 6000 rpm's out of my moter running it wide open.
To perform a leak down test do I connect pressure gauge to each cyl. crank it and let it sit for a period of time to see if the presure drops ? If all these steps you guy's have suggested corrects my problem you've saved me ton's of money ! Thanks, Mike

[robert graham]

WOT means wide open throttle, and in your case, trimmed up, should be near 6000RPM's. Change your oil now and then check it often for rising on the dipstick, smell of fuel in the oil. Four days of *****ing is a lot, maybe mount a kicker motor for *****ing? Good Luck!

[robert graham]

My son runs a F115 Yamaha similar to yours, and I've noticed that these 4 stroke motors purr along so quietly and smoothly at low to idle RPM's that folks may just forget to run the hound out of them at least once or twice a day. Good Luck!

[billyr12x]

my Dad's 2001 115 is doing the same thing it is puring oil out of the dipstick , I checked the compression and it ranged from 130 to 155 on all four . would the fuel pump cause this much pressure out of the dipstick?

[bajakeith]

oil problem

you might want to check or replace your therms !!! if stuck open you oil wil;l "wick"

[Searider]

@Towboat1
I know that this thread is already quiet old but since I have the same problem with crankcase pressure with my F100 I am interested what was the reason for your problem !

My motor does not "make oil" - it has just crankcase pressure .
I use only synthetic oil from Mobile - so guess carbon in the ring groves should not be an issue .
My WOT is usually close to 6000rpm with a 17" Ballistic and my fuel pumps are not leaking .
Can make compression / leakdown test only next month .

Also question to the pro´s - where is the connection between "making oil" and crankcase pressure ???

[rodbolt17]

as the pistons move up and down the crankcase will alternately pressurize and depressurize, its normal.
outboards, so far, do not use a positive crankcase vent system.

making oil.
this occurs when the crankcase oil becomes contaminated with fuel.

a ruptured fuel pump diaphragm can dump raw gas directly into the crankcase.

a stuck t-stat will cause an over rich fuel mix and can push excess fuel past the rings.

over propping will do the same.