Black soot - open throttle

[NYSail]

Hello all, I have a Yanmar 3HM35F (1986) in my Pearson 36-2 that I bought last year. I have replace all fuel and water hoses, flushed cooling system, new primary fuel filter, new mounts, and new mixing elbow. My slip is 10 minutes to the open water where I stop the engine and hoist the sails so I maybe have 10 hours on the engine myself. I have no history from the p/o. Engine runs smooth, oil still golden from this years change. I usually come out of the harbor at about 2,000 rpms and have not really exceeded this until last night. On my way out, I opened the throttle to full. The rpms stayed around 3,000 and black soot and some smoke was coming out the exhaust. I ran it like that for about 10 minutes. Then I reduced the rpm's to about 2,000 and smoke and black stuff went away. I sailed into the harbor so did not max out throttle, however the engine ran smooth with no signs of soot or smoke.Could this be a build-up due to my not running the engine at open throttle? Will this clear itself with a good long open throttle run, or is there something that should be done? Thanks as always!Greg

 

[Don S/V ILLusion]

probably not a problem

the black, as you probably already know, is unburned fuel sometimes caused by an overpitched prop running at max rpm. It could also be as simple as a dirty hull causing more drag and therefore more load on the prop. If the engine had lots of carbon deposits in the exhaust elbow area, it would not be visible in the exhaust and would restrict exhaust pressure such that you would not be able to attain max rpm.You may also know that it's a good idea, once you solve your mystery, to run at max rpm periodically which is better for engine longevity than 2000rpm.

 

[MoonSailer]

Over loaded Condition

A diesel will add fuel to try and get the desired RPMs. If there is too much resistence it can't get the rpms and gets too much fuel resulting in soot. Resistence increases as speed increases in a displacement hull. A dirty hull or fouled prop will also increase resistence. With a clean prop and hull and no strong headwinds an engine should be able to reach max RPMs. If not the prop may beed to be repitched. My Pearson 323 with a MD11C would not reach 2500 rpms until I repitched the prop. When I tried to reach 2500 it would smoke a lot. Now it only smokes when cold and this stops as soon as the engine is warm. Horse power is a function of rpm's and torque. Too much resitence results in too much torgue to reach maximum rpm and maximum horsepower. Also chronic over load will hurt the engine...according to Calder's book on marine diesels. I think that it is desirable to reach maximum rpm's at about hull speed. This allows the engine to have enough reserve power to deal with strong headwinds etc.

 

[Rick9619]

Is the prop stock

NY, I agree with Moon and Don said the key words to ya. You may have an "overpitched" or just uncorrect prop. You have pretty much a rebuilt motor, but your RPMs are low. You should be able to get 3300+ or - 100 out of your engine. Carbon build up is blue smoke. White smoke is water being burned. Steam is an overheat condition about to happen. Check the specs on your prop. Oh and you said your oil was still golden. That will change when it turns ugly black.... which is normal.Cheers

 

[Honeyman]

Mack Boring says...

one of the worst things you can do with your diesel is NOT run it hard for long periods of time. They recommend that at least once a month, go out and act like a powerboater and motor around for 2-3 hours at 75-80 % of max. rpm. What the others have said about props, dirty hulls, anything restricting your engine's ability to turn up to it's max. rpm is gospel. Your 3 cyl. Yanmar is probably governed at around 3600, with 32-3400 as a recommended upper limit. That engine should cruise all day at 2800 and have you at or near hull speed, with no smoke

 

[M Breeden]

black smoke

I agree that a mismatched prop or a fouled prop are the most likely causes of your low max rpm’s and smoking. These are conditions that must be corrected or you will damage you engine when you need it the most, like in a storm. If you change the prop and the condition does not clear up then I would look to a restricted air flow as the next problem. Be sure to check the exhaust pipes as one boat we owned built up a carbon deposit at the end of the exhaust manifold and developed the same problem as you are describing. We change the prop and had the engine rebuilt before we found the problem. I hope changing the prop solves the problem as it is the simplest answer. Good Luck

 

[NYSail]

prop pitch

I do have some growth on the bottom and planned to clean this coming weekend. How does one find out the proper prop pitch?Thanks!

 

[NancyD]

Does it rev up ok in neutral?

We had a similar problem with the same model engine in our P36-2. It was due to barnacle build-up on the prop and prop shaft. You can rev up the engine in neutral and see if it reaches 3200 rpm with no smoke. If that seems ok, you should make sure the hull and prop are clean before fooling around with the propeller pitch.

 

[NYSail]

Excellent

That is what I plan to do this weekend......have the mask, flippers, brush and scraper all ready!Thanks!Nancy, Where are you and your P36-2 located? I am in Mt. Sinai.Love to see P36-2'sGreg

 

[Rick9619]

correct prop

NY Sail, I tried googling your boat and could only come up with the fact that it has a 1 1/4 shaft and a two blader that came stock. I also found a pretty cool site about Pearsons.. its www.Pearsoninfo.net Nancy seems to have an idea although, I will be very suprised if it smokes in neutral. And those must be some big friggin barnicles up there in New York that can drag an engine down BTW, the 36-2 seems like a real nice boat.Cheers

 

[NYSail]

Thanks!

The P36-2 is a great boat for my wife and I. Greatly appreciate the help with this. I do have a 3 blade prop that was put on by one of the p/o's.The barnicles, even a small cluster will definetly slow the boat down and up here on the Long Island Sound they seem to get everywhere fast. I did paint the bottom and prop this year, however the boat sat for a few weeks while I was doing the engine mounts so I may have accumulated significant debris on the prop and bottom. I always worry about reving the engine in neutral and possibly hurting the engine with no load on it. Am I being paranoid?Thanks for all the good advise everyone.Greg

 

[Paul Akers]

a 3HM35F...

...with a standard, 2-blade prop should achieve an rpm of 3400 tops at full throttle. But never run at that. Run at 75-80% which will be 2850 rpm. I typically run mine at 2600-2700 rpm. (This is direct from the Yanmar manual).

 

[Bill Roosa]

Fuel and air

While you are at it, check the air cleaner and mixing elbow. A restriction in either will not allow enough air in at WOT and similarly result in an over rich fuel mixture.Most of these soot and black smoke problems are just regular maintenance ones. Nothing really wrong with the engine but an ounce of prevention .........Run her hard as often as possible. I run my yanmar at 200 RPM below WOT all the time I'm not actually in the marina or getting her warmed up. What is the sense of going slow when you don't have to? And she stays a lot cleaner on the insides.

 

[Steve Dion]

maybe over reving

Greg:I believe that the HM series of engines are rated at 3200 max rpm. If you use the Yanmar rule of 70-80% of MAX rated rpm, then you should be looking at approx. 2200-2600 rpm as you normal operating speed.This calculation assumes that you are using a prop that is properly sized for your engine/transmission etc. You also need a clean bottom/prop/shaft assy when making these assumptions.I suggest that you stay within the suggested RPM range and you will probably be fine. Next time you haul the boat, you can get the prop checked and sized by a prop shop.

 

[Ariel]

Black soot

Greg,Don was right on. It is unburned fuel. I suspect you have a dirty prop. Clean it first and see if the engine does better.As you know, we have cruised from Maine to Texas and back over the years. We cruise at 2400 to 2700 rpm. With about 6000 hours on the engine in the last fifteen years, much of it just running with no load to charge batteries. It is still going with no ill effects, so don't get worred.If you ever get the urge for a small increase in sailing performance and the ability to fine tune the pitch, then consider a fethering prop. Our three blade Max prop has worked reliably for over ten years and we have changed pitch three times to play with performance differances.So, clean the prop and enjoy the boat.PS. This summer we are in the Chesapeake but plan to spend next summer in New England again. Want to get together and compare notes when we pass your location? How about a mini P 36-2 get together? Dave

 

[Big Windy]

Diesels

As several have mentioned...it seems you never "run" your engine...just go in and out of the slip. Diesels like to work and work hard. As Honeyman said, pretend you own a powerboat...take it out and run it. I idle out of my slip to the lake, but coming back in, I lower the sails several miles out, and let tne diesel run for 10 to 15 minutes at 80% wot back to the channel that leads to the slip.

 

[NYSail]

Thanks all...

For the advise. I am going to dive on the boat this weekend and inspect the prop and bottom and will run the engine nice and hard! I did this always with my last boat (1977 Westerbeke), however since this one is new to me and I have just aligned the engine after the new mounts, I was a little tentative about bringing her up....but what am I waiting for carbon build-up? lolGregDave when you are up this way, let me know...would love to see your boat. It is my wife and my dream to spend extended periods and travel on our P36-2 and I am curious to see the modifications that work for you.

 

[Patrick]

Call the Yanmar dealer

Call Complete Yacht Service, 954 462 6977 or send an email to comyacht@bellsouth.net, talk with Mark Malo the owner. Tell him you received this from me and ask him to diagnose the problem.He is the local Yanmar/Perkins dealer here and knows everything there is about Yanmar engines.