Oil loss through oil breather

Tedd · Oct 7, 2020

Caveat: I have never owned or worked on a Universal. Everything I say here is based on other engines I've worked on.

The most common cause for oil loss through the breather is leakage past the piston rings. You should install some kind of collector and monitor the rate of oil loss to see if it's increasing. If you're able to, a compression test would be a good idea. A leak down test will tell you more, if you have access to a leak down tester.

If it's pistons rings, the only really good solution is an overhaul, but that won't be necessary until the problem gets really bad, which could be hundreds or even thousands of hours away.

Stu Jackson · Oct 7, 2020

M25s came with a hose from that fitting down to the base of the engine. You are missing that OEM hose. Here's what many of us have done:

Breather Hose 101 (w/ K&N Filter Pictures from Rick Allen)

K&N air filter breather hose

and Noah's: Oil "breather" hose to Air intake

*************************************************8

You might also find great info here:

Engines 101 - The BIGGEST & BEST collection of M25 Series Universal Engine Information on the Internet, plus some M35, too

Diesel Engine - c34.org

Alan Gomes · Oct 7, 2020

Stu Jackson said:
M25s came with a hose from that fitting down to the base of the engine. You are missing that OEM hose. Here's what many of us have done:

Breather Hose 101 (w/ K&N Filter Pictures from Rick Allen)

K&N air filter breather hose

and Noah's: Oil "breather" hose to Air intake

*************************************************8

You might also find great info here:

Engines 101 - The BIGGEST & BEST collection of M25 Series Universal Engine Information on the Internet, plus some M35, too

Diesel Engine - c34.org

While I think this is a good idea generally (my previous boat with an M25XP had a breather hose that went to the air intake), 1/2 quart in 20 hours seems like an awful lot of oil loss to me. Mine lost nothing even close to that.

Alan Gomes · Oct 7, 2020

ontherocks83 said:
Not sure if this means anything either way, but just to give some back ground, the engine is original to the boat and is a 1984 (36 years old) with only 684 hours on it. The previous/original owner hated motoring and would only use it to get into dock or at the extreme protest of his wife due to lack of wind.

If the engine was babied--and there's reason to think it might have been, based on what you just said--that's not good for it. Diesels need to be run hard. It may be that running it hard for a number of hours would help reduce the oil consumption by re-seating the rings.

By the way: At this point I don't think you really know that all of that 0.5 qt/20 hr. oil loss is all coming out of the breather tube. Setting up a container to catch the oil might clarify that. But it could also be coming out the exhaust. Does the engine smoke at all?

In any event, the oil is going somewhere. It's not uncommon for diesels to burn a certain amount of oil, but 1/2 qt. every 20 hours strikes me as high. Maybe others can weigh in with their thoughts on this.

Alan Gomes · Oct 7, 2020

ontherocks83 said:
Also for the 20 hours I did run it, it has mostly been at about 2300/2400 rpm out of the 3200 rated rpm, which is 75 percent. Obviously there were times where I only ran it for 20 minutes to get out of the marina but the vast majority of those hours were longer runs when there was either no wind or the winds were against us and I had to run it for extended times to get to our destination.

Sounds as though you have been running it properly. But how long have you had it vs. the previous owner?

I purchased a used but very clean Yanmar 1GM, which I installed in my Ericson 26. It started right up and ran fine. However, it did have more oil consumption than normal. I knew that the previous owner of this engine had it in a race boat and he told me that he typically just ran it to get to the starting line, and then back into the slip. After consulting with a local diesel shop that does lots of rebuilds, the very experienced tech told me that what he sees all the time with lightly run engines, often generators, is that the owners don't run them hard enough, and running the heck out of it for a bunch of hours often clears up or at least noticeably reduces the oil consumption. I tired that and, sure enough, the oil consumption has virtually disappeared on my engine. I now make a point to run it occasionally at WOT and it is still good.

Alan Gomes · Oct 7, 2020

ontherocks83 said:
This is my first season with it so the 20 hours is all I have been able to put on it. It was run on the hard periodically to make sure it still ran over the 7 years but that was it. (yes he did run it with water for the intake and always winterized with antifreeze before the winter)

Running it on the hard will not come close to loading up the engine the way it needs to be. Not sure how long he would have run it under those circumstances, but none of that time would have been especially good for it.

Rick Webb · Oct 7, 2020

Excessive blow by can also be the result of a stuck ring in addition to worn rings. A good diesel mechanic can give you possible easy solutions

Stu Jackson · Oct 8, 2020

ontherocks83 said:
Do you have an oil air separator you recommend using before it gets to the air intake?

Some do, I don't. I think anything that gets in the way of the air getting back into the intake is counterproductive.

ontherocks83 said:
Second question, is there a reason this happens or is it just a normal attribute of the engine design?

It is normal.

IMHO, all the detailed analysis that has been helpfully provided is nice, but is not the issue. Either add a hose into a beer can below the engine, or run it to the intake. You are done. I used the beer can for the first 15 of my 23 years with this engine. I have 3680 engine hours, '86 boat, pretty much same as yours.

Alan Gomes · Oct 8, 2020

Stu Jackson said:
Some do, I don't. I think anything that gets in the way of the air getting back into the intake is counterproductive.

It is normal.

IMHO, all the detailed analysis that has been helpfully provided is nice, but is not the issue. Either add a hose into a beer can below the engine, or run it to the intake. You are done. I used the beer can for the first 15 of my 23 years with this engine. I have 3680 engine hours, '86 boat, pretty much same as yours.

I half agree with you here, Stu. If it were my engine, I wouldn't just run the hose into the intake and consider it done--not with the degree of oil consumption described in the initial post. I'd go the beer can route first and really carefully measure the rate of oil loss into the can to see just what sort of problem I may or may not be dealing with. That diagnostic information could prove useful in terms of future decisions. He can always move the breather hose to the intake later, which is a trivial job.

odaydokay · Oct 8, 2020

Years ago (my engine is little brother to your's, a 1985 M-12) I had oil going into the bilge (or pan, I cannot recall) and I found that the fitting on the oil sump where the oil drain tube attaches (your know, top to the oil changes) had loosened a bit enough to allow some drainage. It was hell getting to the large bolt with a wrench but I did and stopped the leak. Not saying this is your issue, but it could be.

Benny17441 · Oct 8, 2020

Excessive blow by could be due to piston rings wear but also could be due to the use of too thin oil. A fairly worn engine should be using at the very least 15W40 and if needed some additive that would thicken viscosity. A thicker oil will improve compression and reduce blow by. Yes, put a hose to that breather tube into a jar or a can to avoid the mess.

RitSim · Oct 8, 2020

Couldn't this also be from leaky valves and valve seals "blowing" oil from the cam area out the breather?

Oil loss through oil breather

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