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Dame.n.Jess · 04-01-2011, 18:23

As an engine re-conditioner it sounds like you have checked almost every normal thing we would look at. One thing that can happen in cars with older engines (years not hours) is the rubber valve stem seals harden with age, this shows up as smoke when at high revs with minimal load on the engine (ie engine breaking down a long hill). I think this is a long shot but some of your symptoms kinda fit into this scenario.

I would always be looking towards it being an oil problem if the smoke is blue, sometimes this rule of thumb is wrong but not very often. Check compression! its cheap (especially if you are buying the gauge and doing it yourself), even if it shows all cylinders are good its more diagnostic evidence. Plus it will give your peace of mind.

I would be thinking possibly rings, possibly unburnt fuel in the exhaust as one guy said (but I don't know anything about that aspect and it wouldn't have been my first guess)

Im REALLY keen to see how this all turns out, I love the tricky problems that dont really hurt anything but are difficult to solve straight away,.

Hillbillyfunk · 04-01-2011, 18:24

Before you go pulling a perfectly good engine apart remember that excess smoke often comes from inadequate air... do you by chance have a dog or cat aboard? I 'fixed' a smoky boat by cleaning all the dog hair out of the turbo/intercooler, your naturally aspirated engine could be choking on a dirty air filter.

Occum's razor applies here

Mark Johnson · 04-01-2011, 18:30

Boden 36... Yes, Yanmars like to be run hard and fast or they carbon up. I have considered running in reverse, but sometimes my prop is only a foot or two off of the bottom, and in reverse, the muddy propwash shoots straight toward the engine raw water intake, 4' away! I hate running mud through the engine. I definetly agree, that these engines should have their regular runs at the dock, IN GEAR. I just have an unusual situation, and I have a slip that fits my 21' width. (hard to find).

David, good points all. Yes it was definetly blue smoke, and I thought that my old problem had gotten worse and was now EVEN under load. Then I remembered plugging the vents, opened an air way, and it went back to normal. (Blue smoke, only @ high idle with NO load)

Actually, after considering a LOT of possabilities, this sounds like what may be going on...

Regarding the diaphram on the lift pump... This was on my list to check out. It is a very long shot, as the oil has NO diesel smell to it, but this very "pin hole in the diaphram" thing happened to a friend, ending in a scarey "run away diesel" situation! I will service this pump...

We have cruised about 20,000 miles with this boat, and the engine has run well and clean under way. (3/4 of it, however, was sailing)... I know I have something wrong, but if it is only happening in this narrow circumstance, I may go back to just living with it. I will, however, service the things mentioned, because they are overdue, and it wont hurt. It might even help?

I appreciate the feedback from all of you.

Mark

ConradG · 05-01-2011, 04:59

Really foesn't sound like there is much wrong with the engine. I wouldn't do anything rash to your wallet yet. Adjust the valves as it is time. Check the injectors if you feel it needs doing (although it certainly sounds like the injectors and timing are fine). Find a friend who's boat you can tow around for a few hour to get the under propped engine well loaded and see if the old "Italian tune up" will help cear the glaze/carbon and seat the rings.

Seems that you are getting fuel to the engine and the timing isn't off. Seems that injectors are in good shape. Under load the somke goes away for the most part.

You do mention that the oil level goes down about a pint between changes. Where do you think that oil is going? It's not abnormal. But it is going somewhere. A very tiny amount of oil will make a big show, especially when there isn't enough heat in the cylanders to burn it more completely (ie not under load).(hey, remember this one if you ever feel the need to be super vissible or cause a distraction-real simple to make a heck of a smoke screen-convenient tube leading right into the intake for oil injection!) The no load-high rpm situation is ripe for getting that tiny amount of oil into the cylanders and not getting it burned well hence the blue smoke.

You mentioned that in the very bigining you had oil consumption that went away shortly-your rings seated, normal breakin. In driving larger trucks we call this the tight stage of break in. "She's tightenned up". You are finally getting to the place where she's "loosening up"! Rejoyce! Your fuel burn should drop now!! (You may not be able to notice it on that engine but in a big rig that gets low single digit mpgs a decimal point or two gain really adds up in a year). When you start to have to ad more than a quart between changes on that little thing then it might be time to think about rebuilding...and then only if you don't have the power you need or are having difficulty starting-it's a financial call, oil's cheap.) As far as the level on the stick goes, I would try letting it find it's own level. Don't let it go below the low (too far) but see if it levels out somewhere. With every diesel I have run it has worked well for limmiting the amount of oil used.

Mark Johnson · 05-01-2011, 06:04

Conrad G,
All good thoughts, but...

The approximately 1/2 pint of oil consumption between 100 hour oil changes, has been there for about the last ten years. The previous (first) 5 years of its life, (= first 1,000 hrs), it used several times that much oil between changes, (3/4 qt), yet then it didn't have this smoking problem at high idle. That would infer an inverse relationship with oil consumption in my case. Hmmm?

The "under propped" comment I made... When I say this I only mean that by say 5%. It is actually close to perfect. The goal with a Yanmar, is to have ones prop where it just will reach the engine's max RPM, but could go no further. (With the governor, how would one know, right?)

Almost everyone I know with a Yanmar is OVER propped. Their engines will not reach the recommended momentary max of 3,600 RPM. I suppose their thinking is that this allows running the engine at really low RPMs, and it will last longer. Yanmar insist, to the point that I believe it now, that these engines need to always be cruised at over 2,600 RPM, with 2,950 RPM being a good, all day cruising speed. (slower speeds being OK, if every hour or two, you wind it out to over 3,000 for ten minutes or so, to blow out the carbon.)

Presumably, our being a Tri and more easily driven, is a bit less load, but the engine / prop is close enough, that if I went up a notch in pitch, I would then be over propped.

As far as the dip stick level. Good idea! I may just suck some out to just above the lower limit line. The engine installation said that the engine was designed to be mounted at (X) degrees. I forgot the amount, but my engine being almost level, and the stick being further toward the back, may mean that I have been keeping the oil at too high a level? Another thing to try... Thanks,

Mark

KEG · 15-01-2011, 17:42

I would suspect worn valve seals. If even a small amount of oil is getting past the exhaust valve seals it will run down the valve stem and burn on the exhaust manifold side of the valve (out of the combustion chamber) and give a blue hue to the exhaust smoke.

I wouldn't under prop or under rev my engine. If it is designed to run @ 3600 then run it there. Oh, and "drive it like you stole it!" Baby'ing engines make them carbon up, coke up and comit suicide. Change oil more frequently if you want but work the **** out of it, diesel especially.

Matthew

Mark Johnson · 16-01-2011, 05:51

KEG,
Thanks, valve seals will go on my list of possibilities. Although keeping it under load when running at the dock, puts off the issue.

My prop is about 98% perfect. It is almost imposable to size one to where it is 100% correct, and I erred on the side of 2% under propped, is better than 2% OVER propped. (This leads to carbon build up). The guys at Yanmar concur with this.

I never under rev my engine, except for short periods of time. My 2GM20-F has a "momentary" max of 3,600, (which one's prop SHOULD allow the engine to achieve, but barely)... a "cruising" max of 3,400, and a factory recommended "sweet spot" of 2,950 RPM. Between this 2,950 and 3,000 RPM is where I run it, as it is where engine longevity, performance, and fuel consumption all like it... "according to Yanmar".

Thanks again for the suggestion.
Mark

Mark Zarley · 16-01-2011, 13:37

Lots of talk about what the blue smoke is, is being what is causing it. Get the engine smoking then stick your head into said smoke. If your eyes water and burn "mild tear gas experience" it is unburnt fuel. If it just smells like burnt oil, it is.