f25 blowby

[CaptSteveR]

I'm new to the outboard world. I have a 2004 F25AET on a tender that I just bought. I did some standard maintenance to it but when ran it and pulled the dipstick while running at idle, air came shooting out with a lot of pressure with a little oil.
Any recommendations on this? Thanks in advance.

[pstephens46]

I believe all 4 strokes will blow oil if dipstick is removed while running.

[boscoe99]

Blowby is indicative of insufficient sealing of the piston rings. Might be worth your while to seriously decarbon your motor. Better still, have a dealer do it using Yamaha's Internal Engine Cleaner. It is the cats meow when it comes to removing carbon buildup.

[rodbolt17]

pull the dip stick while running.
why?????

if the engine is running and you pull the dipstick you get air.
now the crankcase is venting via the dipstick hole rather than the vent hose assy.
kinda like a local boat rental company. added oil to an F50.
forgot to put the oil fill cap back.
rented the boat.
had the boat towed back.
all the engine oil had evacuated via the fill port and the engine was locked.

then they asked if warrenty would cover it.

does your engine have issues or was that normal venting?

dunno.

now would be a good time for a leakdown test.


just as in a two stroke,as the piston travels up air must take its place,that air is now displaced when the piston heads down.

[TownsendsFJR1300]

Just the piston(s) going up and down will cause positive and negative pressures in the crankcase.

There should be a vent tube into the "air silencer" from the crankcase. If there's excessive oil blowing out of there, there's issues...

Search Leak Down test. With a small air compressor and the tool, if the compression rings are leaking, the tool will show a percentage of how healthy the engine is.

**If the rings are worn and you do have excessive blow by, you will literally be able to hear the air (with the tool hooked up) blowing into the crankcase thru the oil fill hole...

[CaptSteveR]

Rodbolt17... good question. As I said I am new to outboards. I have no problem pulling dipsticks out of big diesels and other engines. I pulled the dipstick to see if any oil was being pushed out or if there was a problem, not knowing that I would get an explosion of air shooting out. won't do that again.
Thanks all for your responses. All information helps.

[rodbolt17]

kinda like that fiber in the fill cap on the 871 Detroit.
clog it and it shoves the dipstick out.

trust me.
not knocking anyone.
most auto and desiel techs really really should not mess with outboards.
it is a whole different world with a world apart duty cycle and maint schedule.

as a desiel tech though you should have access to a leakdown tester.
that would be the first thing I would do.
remember so far outboards do not run a positive crankcase ventilation system.
actually it is just about 1 step up from a draft tube system.

[CaptSteveR]

thanks for the response. I'm not a diesel tech but a captain and so I get stuck working on diesels on my clients yachts. Normally I just turn dinghy issues over to a local dealer but I don't have one in this area so i'm working on this one myself. I'm going to run compression tests and if they are good then all else looks good.

[rodbolt17]

compression test= teat on a boar hog.
your rig your time your money.
I have been an auto tech.
a machinist and a CNC lathe and mill programmer.
a second class FC(electronics tech with ordanance quals) in the united state canoe club.
and since about 1989 a full time outboard tech.
passed the Yamaha master tech exam in 2006.
also I am certified for warrenty work on Mercruiser and Volvo gas.
have been certified in the past for Tohatsu,suzuki,Force, mariner and mercury.

take my advice or ignore it.
no skin off my sack.
I started doing this type work when I was 15.
I just turned 55.
my sister is a master RN.
I have more class room hours in training for the past 40 yrs than she does.

biggest difference is she is better looking and can spell. .

[pstephens46]

compression test= teat on a boar hog.
your rig your time your money.
I have been an auto tech.
a machinist and a CNC lathe and mill programmer.
a second class FC(electronics tech with ordanance quals) in the united state canoe club.
and since about 1989 a full time outboard tech.
passed the Yamaha master tech exam in 2006.
also I am certified for warrenty work on Mercruiser and Volvo gas.
have been certified in the past for Tohatsu,suzuki,Force, mariner and mercury.

take my advice or ignore it.
no skin off my sack.
I started doing this type work when I was 15.


I just turned 55.
my sister is a master RN.
I have more class room hours in training for the past 40 yrs than she does.

biggest difference is she is better looking and can spell. .

Is somebody capable of copying/pasting photos from Facebook?

Rodbolt has mentioned looks above....I see that Joes Marine Service has a Facebook page.
Now in the photo section there is a company dinner party photo.
To avoid pissing you off and guessing which one of these fellers you might be...
Would you mind telling us which one you, Rodbolt, are?

[99yam40]

what would a man be doing with a Facebook account?

[rodbolt17]

I will give you a hint.
look up the OBX gun club facebook page.

look for the cowboy action shoot photos.
I am there.

[pstephens46]

what would a man be doing with a Facebook account?

I damn sure don't have one! Prob why I can't copy/paste the pic!

[rodbolt17]

there was one photo or so that I made the xmas party coming straight from my uncles funeral.
I am in dress blues.
my boot camp issue blues.
oddly, they are loose now.

[pstephens46]

Is somebody capable of copying/pasting photos from Facebook?

Rodbolt has mentioned looks above....I see that Joes Marine Service has a Facebook page.
Now in the photo section there is a company dinner party photo.
To avoid pissing you off and guessing which one of these fellers you might be...
Would you mind telling us which one you, Rodbolt, are?

Think I figured it out

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