M-25 Crankase Vent

[Cedric Thevenaz]

I haven't found anything on this issue in the archives. I have a Cat 30 with the M-25 in good condition (around 1500 hours). Engine runs well and has been serviced well (since I've owned the boat for 2 years). Recently I noticed there was smoke coming from the little crankase vent on the top of the engine (a bit stinky for the family). There was no hose on this vent and my local diesel shop said put a hose on it and run it over to the air intake filter. This did the job fine as far as smell/smoke, but can anyone tell me what this may be a result of. I've noticed my M-25 does not run above a temp of 160. The diesel guy told me running warmer would be better but not critical. Another guy told me the smoke is the result of 'blow-by' maybe due to piston rings not fully expanding (which they do only when the engine runs at proper temps of 185 or so) and said not to worry unless a bunch of oil is coming out too (it isnt for me). I've thought about pulling my thermostat and checking temperature regulation. Any help would be appreciated - thanks kindly.

 

[Trevor - SailboatOwners.com]

Same on my boat

Hi Cedric -I actually had oily residue coming out of my M-25 crankcase vent. I did exactly what you did: ran the line into the air intake filter. This recycled the oily air and resulted in no problems for the rest of the time I owned the boat (I logged a lot of hours on that M25!). My engine ran a little cool, close to 170 degrees if I recall. The temp gauge may not be the most reliable, however, and I didn't mess with it because the engine always ran fine.Best of luck,Trevor

 

[John]

crankcase vent

What type of oil and weight have you been using?

 

[Cedric Thevenaz]

Response to John

John thanks for your jumping-in. I have been using Chevron Delo 30W.

 

[Jim Hamilton]

same here

My M25 does the same thing. I also routed the hose to the air intake and all is fine. The surveyor noticed the 'blow-by' before I bought the boat. Instead of paying for a complete engine survey, I asked a bunch of mechanics about it. The biggest thing they said was to test the engine under power for 30 minutes and see if it overheated, started smoking, or the blow=by increased noticably. None of the above happened, and the engine has given me great service so far.I'm not worried about it at all.JimS/V Jimmy Dreams

 

[John]

Cedric

I am not familiar with the Chevron you use. Is it formulated specifically for diesel use? I use Rotella straight 30w. I would also make certain you are not overfilling. I realize this may sound too obvious, but if it turns out to be the case it beats tearing into the diesel. My M25 has no noticeable blowby, but I did route the vent to the intake air filter. Do you have to add oil between changes?

 

[Cedric Thevenaz]

John

Thanks again John. The Chevron oil is what most folks use around here - especially for diesels, so I don't think thats an issue. I don't overfill, however I do notice that once in a while (infrequently) I end up adding just a tad to top it up. Curious, what made you route your vent to the air filter? Was it smoke / smell as well? Cheers!

 

[John]

Cedric

My former boat had a yanmar with no vent to the intake and always had an odor which eventually worked its way into the cushions. My Catalina 30TR with the M25 and 800hrs runs well. I gave some thought to the pros and cons of running a tube from the vent to the foam on the intake and decided to do it. My M24 with a new thermostat and new larger heat exchanger runs about 180F. You may want to examine your thermostat.