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marine diesel blowby

marine diesel blowby

marine diesel blowby

I have a 2 cylinder 11HP universal (5411).  Recently overhauled by engine compartment has vapors when running.  I was told this is blow by from the engine.  
What is blow by?  Is there a way that I can recirculate the vapors, by fan, into the air intake?

RE: marine diesel blowby

SAILODAY28:  Blowby is when combustion gases "blowby" or pass the oiston rings into the crankcase.  If the crankcase is vented then the gases are discharged into the surrounding area.  A newly overhauled engine should have very little blowby.  It sounds like that either the overhaul was not done or done properly or the engine was not broken in properly.  The gases are not healthy and should be vented outside.

If there is a large amount of gases the engine should eb overhauled and brokken in properly.


RE: marine diesel blowby

it should be noted that in service, "blow-by" often refers to only the visible portion of the mixture exiting the crankcase.  The visible part of the mixture is often composed of oil droplets entrained in the otherwise invisible gas flow.  

RE: marine diesel blowby

I installed a 3 cyl Universal diesel in my sail boat some 20 years ago and sold the boat about 14 years ago.  There was no crankcase vent routed outside the compartment.  There was no visible crankcase fumes nor was there a connection to route the crankcase vent outside.  I think that there is a problem with either the crankcase ventilation system or with the rings seating properly.  Perhaps both.  What I do know is that any modern engine should not have the crankcase ventilation dumped into the bilged.  Most engines have the crankcase vent plumbed into the intake manifold.  Universal was acquired by Westerbeke in the early 1990's and you should be able to get the service/installation manual for your engine.  I believe the early atomic 4 (25 hp, 1947 through ???? vintage gasoline engine) did have the crankcase vent dumped directly into the bilge.  The later diesel models did not.

RE: marine diesel blowby

Thanks for the constructive input. However, are there any thoughts on a method for using a fan to push some of the blowby vapors back into the normal air intake.  The air intake is approximately 1 sq. inch. OR is simply don't mess with that?

RE: marine diesel blowby

If the "recently overhauled" engine isn't broken in yet, then I would expect more than normal blow by until the rings seated properly.

Not to say that other things might not be involved as well with your situation.


RE: marine diesel blowby

A small amount of ring blow by is normal.  What is not normal is to have so much blow by that the crankcase ventilation system cannot keep up with the flow.  As such, either the existing crankcase ventilation system needs to be repaired or there is a serious ring sealing problem. There should never be a ring seating and blow by problem provided the cylinder bores are round without taper and there is a proper finish on the cylinders after machining.  Many inexperienced people re-ring a motor with out of tolerance cylinders and end up with problems of excessive blow by.  I suspect that is your problem.  Inspect the manufactures crankcase ventilation system for proper operation.  If everything there is in good order, pull the motor down and fix the problem.  

It could be possible that excessive exhaust valve to guide clearance is adding to the problem.  Again, I would fix the problem and not try to mask the problem.     

RE: marine diesel blowby

The following was put together a few years ago in a non-technical way to explain some aspects of crankcase ventilation mostly specific to high output marine diesels-- The basic principles apply to all and maybe one or two points can be gleaned help you with your question.. In your case, I'd probably want to put a few dozen med to hard hours on the engine, change oil and then do a proper investigation as to your concerns about visible crankcase blowby..In the mean time, be sure of your oil pan level in that you are not overfilled................Tony


SOME THOUGHTS ON CCV's  / Seaboard Marine

Most of the modern diesels of today (2-15 liters or so, where most of my experience lies) have a minimum of ring bypass and create very small amounts of crankcase blow by.. That is not to say that the breather on a Cummins engine (let's say) doesn't have some "puke" dripping from it on occasion; it means that they're other factors involved besides ring bypass... In the case of the Cummins "B", this engine is very susceptible to overfill of the crank case w/ oil and on an "inline drive" the problem gets amplified as the rise of the bow during operation exaggerates the build up of oil in the rear of the oil pan, causing "whipping" of the oil. This has a tendency to push the oil out the rear breather in some cases... The same engine turned around in a V-Drive install may not show this problem... Another factor is the build up of "condensation" (moisture,  etc) that leaves the crank case as the engine is running. This is where a "closed" system can offer some value... I personally prefer a "catch" bottle to monitor the "puke" that comes out of an engine... In the case of the "Walker Air Sep", for a Detroit w/ gobs of crap coming out of the crank case in some cases, this system has proven to be a "godsend" to many... In the case of an "Air Sep" on a modern Cummins B or C, I say NO, as I don't want the "puke" to dribble back into my engine.. The "Racor" and some others, on the other hand, have a collection capability and one can drain the ugly stuff on a regular basis and also monitor its amount.. Generally,  engine manufactures will be forced to come up w/ a type of closed system over the years for all the diesels.. In its simplest of forms, it's merely a mechanism that enables the crankcase to see a "low pressure area" and allow the "fumes" to be burned during combustion, while separating most of the liquids...Yanmar and some others use a very basic system by putting the crankcase hose near the air inlet and accomplish this "low pressure" thing.. Another problem that has come up with these systems is w/ "sea water after-cooled" diesels; a lot of these "fumes, puke, etc." don't make it past the cold after-cooler to the combustion chamber, causing increased maintenance of this accessory..

 So what is the answer? On a new Cummins "B", a "catch" bottle, or, if you have to have a CCV, go w/ the Racor type and drain it on occasion.. Remember that in ALL cases, all of the plumbing used for these systems MUST be designed to drain completely during any type of operation.. In particular w/ the "B", a loop was created in some of the "Air Sep" installs just after the case vent. This created a "liquid trap" (like under your sink), effectively sealing the crankcase from even breathing at all... (couch engineering)..

In the case of Volvo's or other manufacturers systems of containing crankcase blow-by, the same basic principles will apply. From my experience with any modern hi-speed, 4-stroke, turbocharged, sea water after-cooled "balls to the wall" horsepower per cubic inch marine diesels, which seem to also have relatively shallow oil pans that cause more than normal turbulence from whipping of the oil, crankcase blow-by is a current problem that is being looked at by all manufacturers.

 On a GOOD engine without a scuffed piston, stuck ring, or ?????, there is a certain amount of blow-by/crankcase fumes and possible oil that gets "whipped" out the breather hoses. In a fairly recent case (in my area ) with a Yanmar 6LY/315, the crankcase was overfilled (not the engine manufacturer's fault) and upon using the boat the crank whipped and threw so much oil out the breather tube (which happened to be attached to the inlet of the turbo) that the engine decided that this was all the fuel it needed. It went to (probably) 5000+ rpm before it self-destructed. The point I'm trying to make here is that a breather system needs to come from a "QUIET" area of the engine. The placement and design of this system needs to be looked at from more than one perspective......case in point -- CUMMINS: their couch engineers seem to think that all engines are installed in boats in the same direction and all boats operate at the same angles,,,,, whatever,,,, With the supposedly "tried and proven" crankcase breather location on a Cummins B (which is on the left side/rear of the block,) they've actually chosen a lousy location for the higher HP/RPM engines in in-line drive applications. The oil pan is so shallow that it causes excessive whipping of the oil in many applications, and leads to excessive crankcase blow-by.

So, what am I really trying to say here? First, all crankcase ventilation systems CCV’s,  need to address the operating characteristics of the installation. In-line drives are usually "nose up" and therefore, it should be common sense to find an area towards the forward high part of the engine (valve cover, timing cover) to attach a breather hose. This hose should be routed to a device to allow liquid separation before the gases are sucked into the intake. As for V-drive installations, they are typically "nose down" during most operating conditions and need to find a high quiet area for crankcase breathing near the back of the engine (bell housing end.) The low pressure area of the air inlet can be used effectively to burn / re-circulate gases from normal crankcase blow-by, but needs more individual engineering to adapt to all applications...

So, what might be this perfect "closed" crank case ventilation system in a boat?? In my opinion it would be one that could ingest all of the normal (and a little extra) crank case bypass from a modern "state of the art" marine diesel, separate all of the gases from the "pukey liquids" that will fowl after-coolers, turbots, etc., let the liquids be captured and drained in a convenient way to discarded, and that by burning these crank case by-products, that we don't create some other high maintenance problem....

As for the Volvo TAMD 40++ series  question which prompted this article, these are "state of the art" marine diesels operating at levels un-approachable just a few years ago.. These operating conditions will dictate that more control w/ be necessary over crankcase bypass, exhaust system design, prop loading, etc. etc. etc.. These operating conditions/parameters are not unique to Volvo, but are common to all of these competitive marine diesels that are giving us a new feel for diesel technology.

Tony Athens

RE: marine diesel blowby

I now have excessive lube oil loss.
Shipyard stated and replaced dip stick.  Stated loss was via pressurized crankcase via unsealed dip stick.
After taking the the boat out for spin, lo loss continued.
A shipyard advised that they would not take on the job.  They have stated that during idle,very little if any LO loss, but with engine load losses occur.  I can't see the leaks.  Is there any additive to LO that will allow me to use something like a black lite to detect leaks.


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