No High-end Engine RPMs

ALNims · Jul 16, 2015

kenvail said:
I was on a two-week trip around Long Island recently and developed an engine problem with my Yanmar 3JH4E diesel engine. I was getting a lot of blue exhaust smoke, an oil sheen on the water and couldn't get the engine above about 2,000 rpms under load. I changed both fuel filters but it didn't change the symptoms. Any ideas?

Maybe you have bad piston rings. If you are getting oil out of the exhaust and blue smoke suggests oil being burnt. Oil can be pumped past bad rings into the cylinder combustion chamber. Low rpm's under load maybe due to loss of compression. I would stop running the engine and get a qualified mechanic to look at it. Has your oil level changed? How does the oil look? Is the level dropping. Is it dirty?

uncledom · Jul 17, 2015

kenvail said:
The oil level has not gone down, if anything it is going up! I have smelled the dip stick and it doesn't smell of burnt oil or of diesel fuel (so why is it rising - if it really is?). I will be checking closely this weekend and speaking with the yard mechanic. Thanks.

Knowing if it is rising or not is a big piece of information. Have you had the bottom cleaned before the trip, checked the prop for fouling? It seems from your description that something is causing the engine to lug. That can easily be a physical symptom like fouling. Can you bring the engine to full throttle in neutral?

Benny17441 · Jul 17, 2015

Low RPM could be due to fuel starvation or blocked exhaust. You did well in replacing the filters but make sure there is no clogging at the fuel tank pick up tube, that the vent is clear and that the fuel pump is not leaking and delivering proper pressure. If your oil level is rising it could be that the fuel pump diaphragm is perforated and allowing diesel fuel to enter the crankcase; also that would explain the loss of RPM as the pump looses efficiency and cannot supply enough fuel to run the engine at higher RPM. Actually the diesel fuel will thin out the motor oil allowing it to blow by the rings producing large amounts of blue smoke. Thicker oil will increase compression while thinner oil will reduce it. A fouled bottom or prop will usually result in overfueling which produces black smoke.

ALNims · Jul 17, 2015

If it is going up it maybe due to blow by from the combustion side of the piston into the sump. Do you have the ability to test your oil for thickening?

ALNims · Jul 17, 2015

kenvail said:
no I don't, but maybe the yard does. I'll check this weekend.

Best of luck on this one. Also if they can do compression checks on your pistons you may want to consider that also. Compression checks can be done with a keine indicator gage with the engine running and will tell you real quick whether or not you have a ring problem.

cjfj · Jul 19, 2015

Compression check should be done to know if rings or valves are bad. A quick check is with eng running chec if you have high pressure at the rocker cover vent. Don't try if eng is hot but if you have oil leaking from the hose or an air leak get a mechanic to do the compression test

ALNims · Jul 19, 2015

kenvail said:
Thanks all for your ideas. I've spoken with our yard mechanic and below are his reactions to your ideas. One thing I didn't mention with my original post is that the problem came on pretty suddenly. We had a 12-mile trip from Martha's Vineyard to Cuttyhunk. It was during this trip that I noticed the lack of upper end rpms and the smoking, meaning that it came on pretty suddently. We had run the engine for about 30 hours prior to Martha's Vineyard. The last time I got fuel was at Lake Montauk, NY, a very active fishing and charter port - the last place one would expect to get bad fuel.

Yard mechanic's comments about your ideas:

> Mixing elbow: Possible, but the problem would creep up over time, not come on suddenly.
> Compression: Probably not because low compression would result in difficult starting which I don't have.
> Fuel getting into crankcase: No, the oil does not smell like diesel at all and is not thinned.
> Fouled prop: Again possible, but unlikely because of new paint, but will be diving on it next weekend to look.

I bought the boat a year ago and was told it had been lightly used. The hours meter doesn't work but there can't be 1,000 hours on it. Even if it has 2,000 it is a young engine.

Personnally, I think it could be the fouled prop (diving will determine that soon) or a clogged injector.

Thanks for your interacton. Any other ideas or comments??

Please let us know what you find out.

ALNims · Jul 19, 2015

kenvail said:
I was on a two-week trip around Long Island recently and developed an engine problem with my Yanmar 3JH4E diesel engine. I was getting a lot of blue exhaust smoke, an oil sheen on the water and couldn't get the engine above about 2,000 rpms under load. I changed both fuel filters but it didn't change the symptoms. Any ideas?

I have attached a copy of the Yanmar Shop manual Vol1. On the attached page it describes what causes blue smoke. I strongly encourage you to read this. The paragraph describes piston rings, Overfull oil sump, Bad valves, clogged crankcase exhauster or damaged cylinder liner. You may want to try lowering the oil sump level first. I would also ensure that the crankcase Breather is not clogged. I have attached three files describing what the breather does and the maintenance procedure. The procedure is very easy. After doing both the sump oil level and breather maintenance, I would then start the engine and see if you have cured the blue smoke/oil out of the exhaust problem. If not,
contact your mechanic again and ask his opinion again and show him the attachment from the shop manual troubleshooting guide. You may want to consider getting a second opinion. The easy solution is the oil level or crank case Breather.
You can get a full copy of the manual on this website from the manual downloads section. Also were you able to use an oil comparator? If you have dilution from fuel oil the oil from the engine will be less viscous. If you have thickening the oil will be more viscous. The comparator is the only sure way to know. Please let us know what you find.
The manuals are located here.

http://hunter.sailboatowners.com/in...ds&Itemid=287&brand=2&id=0&model=gen&page=gen

kloudie1 · Jul 20, 2015

Kenvail, I think you are heading in the right direction.. chances are you are dealing with a fouled prop .. might be some trash in it.. the only other thing that came to mind (besides a possible bad injector) is intake air.. check the air cleaner to make sure the (notoriously disintegrating) air cleaner element has not packed it in and collapsed, restricting the air flow. Good luck.

Nelsonhow · Jul 20, 2015

Do the simple (and Cheap Stuff) first:

Check prop for a line wrap or other fouling. (The prop should be clean and should spin easily when the engine is in neutral). Check to make sure you don't have rope or fishing line wrapped around the prop and or shaft....check where the shaft enter the hull by the shaft log too.....

Check the replace all filters (secondary --- the big one and primary the one on the engine)

Check to make sure you have clean fuel. If you have any doubt drain it out and put fresh fuel in the system.

Check to make sure all fuel connections are tight and not leaking.

After you've done these you can do the other more expensive stuff. The Yanmar engines, especially the old ones, are just about as bullet proof as possible, so before you jump the gun check all the easy stuff first and let us know what you find....

Don Lucas · Jul 20, 2015

bad injector

No High-end Engine RPMs

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