# Ink black exhaust water - soot?



## sandycohen (Dec 20, 2009)

I bought a 1979 pearson 32 about three months ago with a Yanmar 2gm20f. Until last week I ran the engine at around 2200 rpm cruising. Then I realized it wants to be run higher and recommended speed is 80 percent of max. So, the last time out I cranked her and all was well. Today went out and after five minutes noticed black stream in the exhaust water (not smoke). It may have been there from go but I didn't notice. When idled down no black. When run under high rpm with no load (neutral) no black. I took a sample of the black water and it is not oil, it's sooty. Engine doesn't seem unusually hot and gas who be fine. Don't know about filters, haven't checked. 

Is it possible that the two hours max i ran engine at 2000 cruising over a couple of months built up so much soot in the elbow or muffler that i just need to blow it out by running at high (correct) speed? I didn't persist since black stuff coming out the back the boat freaks one out. 

Bottom is clean and i don't think there's a prop issue (it's folding) and there is no rough running, trouble starting, speed fluctuations etc.. 

Thanks!


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## bubb2 (Nov 9, 2002)

It is unburnt diesel. Chances are you are over prop'ed. To much pitch and the engine can not reach full RPM and burn all the fuel you are trying to feed it. Try adjusting the folding prop, back off on the pitch.


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## sawingknots (Feb 24, 2005)

bub is right,the black soot is caused by overloading the engine,yanmars are famous for this,what makes you think it needs to run at a higher rpm?throw the tach away and use your better judgement,higher rpm's should only be used in an emergency situation and only for a very short peroid


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## sandycohen (Dec 20, 2009)

1. Per the original post, is it possible I am just blowing out carbon buildup in the system from my low rpm runs? Is it dangerous to the engine to run with the black exhaust water to test the theory?

2. Everywhere I look online says Yanmars DO want to be run at 80% of max output which would be 2720 - are you saying that is wrong??

3. The PO installed the folding prop and didn't have this problem.


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## bubb2 (Nov 9, 2002)

Sandy, soot comes out of a engine as black smoke. I have a 2gm20f in my Beneteua. Your problem is one of two things, fouled prop or to much pitch. This is why you are only seeing the problem when you put the engine under load and not in neutral. Soot is black smoke, unburnt diesel is black ink in the water.


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## sandycohen (Dec 20, 2009)

Bubb - Is there anything damaging to the engine about having black ink in the water, other than to the environment?

Am I correct that it is necessary to correct the pitch, rather then just idle down and achieve the same speed, because then i am running too low an engine speed which will cause soot and black smoke?

The stuff in the water is black particulate - is that what unburnt diesel looks like? 

Guess I better read up on what pitch is and how I adjust it!


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## saillife (Jun 25, 2006)

It is a good idea to run the engine 75 - 80% of max. Diesel engines like / want to be run.This is what Mack Boring will tell you if you take one of there maintenance classes. In fact the guy teaching the class suggested going out once a season for a couple of hours and running the boat like a powerboat. The issue for us sailors is that a lot of time the engine never gets a chance to run at operating temps long enough to stay 'clean'. I know that my engine only runs for about 20 minuets when I go out and when I come back.


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## bubb2 (Nov 9, 2002)

Dive on the prop, it could be barnacle growth. But if the prop is clean then I would play with the pitch. I am not going out on a limb and tell you that this could not be damaging. What I do know is if it is not taken care of it will get worse. BTW, when I am motoring I am at half throttle or about 2200 rpm. That seems to be the sweet spot for my boat where the engine is the smoothest and I get the best fuel consumption 1/4 gal an hour. The difference in speed is 5.4 knots compared to 6.2 knots at 3/4 throttle and using 1/2 gal of fuel an hour.


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## sandycohen (Dec 20, 2009)

Bubb - You have a 2gm20 as well?

I have an off topic question that another owner could answer - the oil dipstick (on the engine, not the tranny) has a huge distance between the high and low marks - like almost the entire blade of the dipstick - is yours that way too? It seems hard to believe that the high and low acceptable range could be so far apart unless the resevoir comes to a very narrow point where the dipstick goes, or it curves in a crazy way.

thanks!


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## bubb2 (Nov 9, 2002)

I just keep it filled to the top mark and don't worry about anything else.


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## sandycohen (Dec 20, 2009)

Thanks but could you confirm that the distance between your top and bottom marks is quite large compared to the visual diagram of the dipstick marks in the manual, or say a car?

Thanks


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## bubb2 (Nov 9, 2002)

No I am not going to confirm that as I had many cars over the years and what you may think a quite a distant is not to me. If I remember correctly the Illustration in the manual is not to scale.


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## saillife (Jun 25, 2006)

Another thing covered in that mack boring class. The low end of the dipstick on yanmar is the 'enough' mark. Unlike a car it is not the add level. The suggestion in class was to scribe a mark 1/3 of the way from full and make sure the oil level stays above that mark.


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## sawingknots (Feb 24, 2005)

your 2gm has only about a 2 quart capacity,if your having problems keeping at the full level you have bigger problems and to your other question,its a small engine pushing a heavy boat any extra load will cause an overload,over proped,dirty bottem or even a extra large alternator when its fully charging,i run my ysb 12 at about 1/2 throttle [no black smoke]and don't get much more significent speed at more,btw your tach may be wrong


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## sandycohen (Dec 20, 2009)

Bubb - Sorry if I have gotten your bad side, not sure why you don't want to agree on anything that you seem to agree to.

For everyone else - an update:

Went out for a sail today. 

First,- there is a foam air filter, and removing it had no impact on anything.

Second, prop is clear and unfouled, as is the bottom - I dove and checked - beautiful day to swim in Lake Pontchartrain.

The black exhaust water (I am going to stop calling it soot) starts to appear around 2300rpm, and gets progressively more black and less clear water as I go to 3100rpm. 2300rpm is about half throttle (based on the pedestal throttle control range, not the actual throttle arm on the engine, i didn't adjust or check that). I can get to 3100rpm at say 3/4 throttle and from there on engine speed will not go any higher nor does the engine sound any louder. Also, make speed seems to be about 2700rpm - additional engine speed doesn't make us go faster in the water that I can detect.

At 2200rpm I can move the boat around 5.5knots into a 10 knot headwind. That seems like an acceptable speed given the headwind.

Inside the sheltered harbor, I could only get to maybe 6.5 knots top with full engine speed - which is less than hull speed - more engine speed didn't make any difference.

Also I want to clarify that the stuff i am calling soot which is inky black water of varying concentrations in the exhaust, is suspended flaky particulate in the water (I took a sample) it isn't fine particles or liquid.

Also, even when I am at 2200 and the exhaust water is clear, if I take a sample of it there is some suspended particulate.

The amount of force ejecting the exhaust water doesn't seem to change tremendously as the color gets more and more black. This makes me think it isn't "cleaning" residue from the exhaust system, or it would always be the same. But my mechanical understanding of the exhaust system is nearly 0 so maybe I am wrong.

To where we left things yesterday, I am certainly happy with 5.5 knots cruising in a light headwind, as long as running at 2200rpm isn't doing me damage.

And, the biggest thing perhaps, as sawingknots pointed out wisely, is that my tach could be wrong! But, my idle shows about 800 to 900 which seems right. And, would this explain having 1/4 of my throttle travel show no change in engine speed?

I welcome everyones comments. I did not open the elbow yet, and I certainly can, but wanted to share this info first.

Thanks to all.


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## sawingknots (Feb 24, 2005)

no problem,i really think you are ok just run it at that speed,btw i have a ysb12 and it does about the same way except i put on an extra large alternater,bad idea,i have to wait until the battery is recharged before the black stops


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## bubb2 (Nov 9, 2002)

You haven't got on my bad side. I am just a cranky old man that has been around boats for more than 50 years. The reason the exhaust gets darker as the engine speed increases is as you are increasing the throttle the more unburnt fuel you are putting though the engine. Do you know when that prop was put on the boat? Did you do a sea trail when you bought the boat? If you did have a sea trial was the engine ran at full throttle for 5 to 10 Min's. When you bought the boat did you have oil analysis done to check for particulates and contaminates in the engine oil including unburnt diesel?


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## mitiempo (Sep 19, 2008)

You are close to your hull speed at 6.5 knots - hull speed being 6.7 knots for your waterline of 25'. 

The correct prop will let you achieve max rpm and ideally no more. If the revs exceed max rpm under power you are under propped. If you cannot hit max rpm you are over propped. 

I would check the exhaust elbow in any case. If it hasn't been checked in recent years it could be restricted by carbon. They regularly corrode from the inside as well. 

When an engine works too hard it will exhaust unburned fuel.

An accurate tach would help.


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## captbillc (Jul 31, 2008)

i have a 2GM20F. most of the time i run at 2250. this does not hurt the engine, & saves fuel . wide open it will get up to 3600 and 6.9 kn which is hull speed. no soot. if your engine will not go to max rpm your prop has too much pitch.


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## bubb2 (Nov 9, 2002)

copied from another forum

*Black Smoke and Exhaust Problems*
_I am hauling our boat soon and I was wondering about our prop and if it is the correct size for the engine. I say this since the engine will start to blow black smoke once it reaches 2900-3000 RPM. Dave_

*[JED]* This must be corrected, as you are limiting the useful working life of the engine. Possible reasons for black smoke - 

prop pitch is excessive [engine is overloaded and is running too rich]
dirty bottom or prop
transmission problem
old fuel [very common]
kerosene being burned instead of diesel fuel
air inlet restriction
turbo problem [only for turbo charged engines]
engine cannot get enough air while running at high rpm [engine space not properly ventilated]
restricted intake or exhaust valves
improperly adjusted valves
restricted exhaust system
injection timing incorrect
injector problem
low engine compression
engine is not reaching correct operating temperature
I would check the simple things first, as in the list above. Did your boat always have this problem, or did it develop suddenly, or gradually?

If your fuel supply [in the boat] is more than 6 months old, and no fuel stabilizer has been added since you filled the tank, it is suspect. Most sailboat fuel tanks contain at least SOME very old [several years] fuel. The tank should be pumped dry, inspected for condition, and fresh fuel [with stabilizer] added. Also change all fuel filters.


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## bubb2 (Nov 9, 2002)

if you had a restriction in the exhaust it would show up both in neutral at full throttle and in gear at full throttle.


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## mitiempo (Sep 19, 2008)

It would be more of an issue under load though than full throttle in neutral.


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## Izzy1414 (Apr 14, 2007)

bubb2 said:


> You haven't got on my bad side. I am just a cranky old man


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## bubb2 (Nov 9, 2002)

mitiempo said:


> It would be more of an issue under load though than full throttle in neutral.


agreed


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## sandycohen (Dec 20, 2009)

Hi All - First, thanks again for everyones input.

Two things to add to the thread.

First, I opened the boat to full throttle in idle to see what max RPM I could get to. The answer is about 3400 and the throttle control is hitting the transmission lever which in neutral is right behind the throttle control which in the real world wouldn't be a problem since it isn't necessary to go wide open in neutral. While trying to inch the transmission control down to find the end of the throttle travel, i accidentally (although I guess I should've seen it coming!) dropped the tranny into reverse at about 3500rpm - probably did more damage then the rest of this issue ever will (seriously, does anyone think that one time shift is something i need to worry about or do anything to check damage - I shifted in idle several times fwd and rev after and all seemed fine).

So, it appears in idle the engine can hit max rpm's or something every close to it.

I did get inky water in idle running high rpms the first time I opened it up wide. The 2nd time I did it againt o try and find the rpm where it starts and it didn't turn inky, but i would say the water still had a grey tint and there was greyish exhaust smoke.

To point out something else I've never said before, I normally get NO exhaust smoke, and even when i have inky water there isn't always any visible exhaust color.

The next thing I want to report is that the PO responded to an email from me asking him if he'd ever seen inky exhaust water, what his cruising rpm targets were, and if he purposefully overpitched the prop - response is below in a couple of threads:

From PO in reply to a voicemail I left him:

_Anyway, black exhaust is usually caused by unburned fuel, in turn caused by engine overloading - for instance, the throttle is pushed all the way up calling for more engine speed, but the engine just can't get there because of big waves, heavy load, or the displacement hull just won't go any faster.
I think you mentioned something about max rated engine RPM. You are only going to get there if the prop is perfectly pitched for the particular boat and engine combo, which can be hard to achieve in the real world.
So, in reality, if you see black exhaust water throttle back just a little and it should go away. If you want to pull the exhaust elbow it can't hurt anything, but it might turn out to be a PITA job. Hope this helps.

My reply:

Basically since I had the boat I had been cruising around 2200rpm - I think maybe this is what you told me was your guidelines. Then I read things online that says the engine wants to be run at 80% of the rated continous rpm, which would mean a cruising rpm of something like 2800-3000. When I started doing that I got the inky black exhaust.

I've posted the issue on two message boards and gotten a lot of great advise. I didn't think the issue could be pitch (what people call being overpropped I guess) since you had bought the prop special I figured you got the appropriate size one. Some people did say that some owners intentionally overprop the boat to reduce noise and fuel consumption by running lower rpm's - did you do that on purpose?

His reply:

Yeah, the boat might be a little overpropped, but not on purpose. I installed the prop the dealer recommended, and it wasn't worth it to me to haul the boat back out, send the prop back, and install another one to get the pitch just perfect. I think 2400 RPM or so would be a good long-distance cruising speed and 2600-2700 if you were in a hurry and not too concerned about fuel consumption. It's not so much percent of rated RPM that you are looking for, as much as percent of rated power output. If the prop is perfectly pitched, the two go hand in hand, but if the pitch is a little high then you get higher power output at a lower RPM_.

I bought the boat largely based on my experiences with the PO and knowing that he is both more knowledgable on all systems than I am, and more careful/concientious I suspect than I am on taking care of things. So I am going to basically now use his RPM guidelines, maybe check the elbow when I get a chance, and forget about it! But, since everyone got behind me to try and figure this out, I wanted to give you more info, and if you want to keep discussing or have other thoughts, please share.

Disclosure, the PO is now probably reading this thread so be diplomatic.


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## sandycohen (Dec 20, 2009)

Forgot to add - I used decompression levers to check both cylinders, and with either lever thrown the engine sounded awful, so I think that means by injectors/valves are OK right?


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## mitiempo (Sep 19, 2008)

Decompression levers are for starting, either by hand or to help spin it before electric starting. I've always heard that releasing the compression on a running engine is a good way to do some serious damage to the valves and wouldn't recommend it.


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## sandycohen (Dec 20, 2009)

Uhoh - I hope what you've heard is one of those hyperbolic tales that is a warning of something that could but usually doesn't happen.

Can anyone else chime in on whether flipping the levers very briefly at idle speed in neutral may have damaged the engine, and what I can check to see if it did indeed?

Sandy


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## mitiempo (Sep 19, 2008)

Probably less risk in neutral than at higher speeds. As far as I know the decompression levers keep the exhaust valve open for easier rotation of the engine for hand starting. When the engine is running those valves open and close each time a given cylinder fires. These 2 actions are at odds with each other and ultimately something will break.


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## arf145 (Jul 25, 2007)

I believe the decompression lever on the 2GM20F just pushes the exhaust valve down some so it is open. I tried this once on my 2GM while idling... and it immediately snapped closed--I don't think it is meant to be messed with on a running engine. Then again, I doubt you hurt it.

No one else has mentioned this, but it can't hurt to check your valve clearance. You sound like someone not afraid to mess with stuff  and even if it has nothing to do with your current issue, it would be good to know the clearances are correct.

BTW, I've read the advice to run the engine at 80% etc. Not a bad idea to do that now and then, but you should cruise at what's comfortable, I think. My boat has the original factory 2 blade prop, and under most conditions 2500 rpm gets us somewhere around 6 knots, IIRC. We rarely use more than 2500.


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## TropicCat (Oct 14, 2008)

I own a boat with 2 Yanmars and would like to suggest something no one else has mentioned.

My engines are very sensitive when using old diesel fuel. In fact it causes the symptom you mention. I would suggest a cheap fix by tossing a couple of gallons of new diesel in the tank and add a stabilizer. I use 2 stabilizers.

*Stabil* to extend the fuel life and *Diesel Clean* to add the lubosity lost in our low sulfur diesel fuel at the pumps these days.

It can't hurt.


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## sandycohen (Dec 20, 2009)

Hi TropicCat - Thanks for the input. Unfortunately I can report that I put about 5 gallons of new, marina grade diesel in with an additive last month, and the tank is only about 20 gallons so that's a pretty good share.


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## SlowButSteady (Feb 17, 2010)

Tropic Cat may still be on the right track. Diesel fuel will polymerize as it ages. This makes it burn more slowly and often results in incomplete combustion (basically, the longer the molecular chains the slower a hydrocarbon will burn). Adding some new diesel will help, but if there is enough really old fuel in the tank the soot could be a result of this incomplete combustion of old diesel. Microbial growth in the tank will make things even worse. 

I would take a look at a sample of the fuel from the tank and compare it to some fresh diesel. If the difference in clarity is dramatic (as in, one look makes you wonder how the engine ran at all), replacing ALL the fuel and cleaning the tank may be in order.


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## deniswithane (May 5, 2014)

Hi, I'm new here and also have black soot coming out of the one engine exhaust with bubbles on the water when running under load 1500 on the mooring and not in neautral. So, it is felt that this is the pitch of the prop? Could well be as I have a re-built prop on that sail drive. The engine has been standing for a quite (4 months) a VP MD2030D with a warranty repair breakdown on the new sail drive, so I will take her out for a run and see if it clears, otherwise look at the prop. My other engine runs clean exhaust and they both share the same fuel tank, which makes me think it is not the dreaded diesel bug! Thanks Denise


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## gamayun (Aug 20, 2009)

It's easy enough to check your exhaust elbow first and see if it's plugged. I started having those symptoms of soot on the water with the engine also bogging down. The elbow was almost completely plugged. They're good for 5-8 years. The manual says that running the engine at higher RPM under load helps to burn off this soot so it doesn't build up as much.


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## christian.hess (Sep 18, 2013)

load it up and clean the exhaust system(elbow), manifold...

always have some sort of stabilizer in the diesel if not used frequently

almost all the time this is caused by clogged exhaust systems...

you will also notice a nice drop in running temps too...as an added bonus


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## deniswithane (May 5, 2014)

Thanks, elbows are new so will be OK. Going to clean exhuast pipes and mannifold. Checked tanks and Raycors, all smells OK - always use additive for dreaded diesel bug in hot climate. Thinking it could be prop pitch related so will swop prop in water Wed and see if that works as I am sure somebody put on a diff prop at some time!


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## deniswithane (May 5, 2014)

Elbows new, will check pipes - only 725 hours on this engine and running very cool in hot water of the Carib.


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## deniswithane (May 5, 2014)

I am so happy  

As I have sorted out my problem on the one engine that the mech said was burnt out oil rings, etc. !!!!

I took off the prop on this port engine (which was a spare as such but was supposed to be identical to both the originals!) and put the old original re-painted one back on and HEY PRESTO, NO MORE BLACK SOOT under load!

So it was the prop pitch after all.

Thank you so much to everyone who pointed me in the correct direction - I have just joined this forum and what amazing feedback I got from all of you, without your input I would never have realised that and would have wasted good money on a mech who did not know much more than me !

Thanks again
Denise


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## christian.hess (Sep 18, 2013)

darn must of been quite the difference in pitch...

congrats!


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## zeehag (Nov 16, 2008)

my cute lil yannie 2qm20h makes the sickest looking stream of black when i havent used it in a while and then use boat. dealer distributor sed it was fine. he also overhauled it less than 150 hours ago when i bought the boat. 
when my perkins did did that, it was past time for major work. (in 
progress)


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## casey1999 (Oct 18, 2010)

I have a 1980 Yanmar 3gmd. I believe same as the OP's engine but 3 cylinder. I think my boat is also over proped as if I run at anything over 2500 rpm the engine just goes faster but boat is already at hull speed so goes no faster. I do not blow black smoke, by the exhaust does become more gray and the engine seems to start running hotter and seems stressed.

I have also heard the yanmars like to run at 80% max rpm. But to me, that is really straining the engine. I know what Mack Boring and even the Yanmar manual says, but it just seems to be straining the engine, and higher rpm mean more wear on moving parts. I do however run the engine in neutral for 30 seconds or so at full rpm prior to shutting down- to blow out the carbon as the Yanmar manual says you should do.

I believe my engine has been run this way for the past 34 years and does not burn oil or have low compression. Exhaust is clear.

I would just run your engine at the lower rpm if that is what your boat is happy with.

The I also agree with the OP's PO- it is difficult to get the perfect prop specs considering the effects of wind and waves will have on the load the engine will see.

As far as the engine oil dip stick, sounds to me the your range is too wide, I would go to a yanmar supply and compare what they would have for your engine


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## deniswithane (May 5, 2014)

Not easy to see the diff without looking at the numbers, which were rubbed off! I am so thrilled as this has cnot cost me a fortune and all the upheaveal again after a 1 1/2 yr warranty cleaim fight with VP over a faulty design on a sail drive fitting my engine which blew the crank case seal after failing for the 3rd time!

I am so happy!!!!


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## jzk (Feb 25, 2008)

Forgive me if this has already been answered, but what is the max RPMs of your engine? Can you hit that at full throttle?

The tone of the correspondence from the OP sounds like he knows it was a pitch problem.


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## christian.hess (Sep 18, 2013)

casey1999 said:


> I have a 1980 Yanmar 3gmd. I believe same as the OP's engine but 3 cylinder. I think my boat is also over proped as if I run at anything over 2500 rpm the engine just goes faster but boat is already at hull speed so goes no faster. I do not blow black smoke, by the exhaust does become more gray and the engine seems to start running hotter and seems stressed.
> 
> I have also heard the yanmars like to run at 80% max rpm. But to me, that is really straining the engine. I know what Mack Boring and even the Yanmar manual says, but it just seems to be straining the engine, and higher rpm mean more wear on moving parts. I do however run the engine in neutral for 30 seconds or so at full rpm prior to shutting down- to blow out the carbon as the Yanmar manual says you should do.
> 
> ...


my 2gm loved to run at 2600-2800rpm

yeah a smaller boat but was higher than most guys like to cruise at

for what its worth I do beleive that yanmars like to be loaded up a bit more

its something I have heard over and over again many places around...

also propping correctly should be done on a new or at least rebuilt engine since with a very old tired engine or simply run long hours wise you might be diagnosing and fixing symptoms caused by other problems and issues.

for example in this case it seemed to be the prop all along, but a tired engine with badly sealing or worn rings, and sticky valves or bad seating valves will exhibit the same symptoms

not to mention the *getting hotter issue* which can be caused by improperly seating valves and carbon buildup

pistons that have a bunch of crap on the domes will create a fake compression and require better cleaner fuel in general terms...so if you find that all of a sudden(it takes years but you dont notice since performance degradation is gradual) you start getting hotter and billowing smoke and soot out the exhaust

BUT you have confirmed your exhaust, elbows, water lifts, manifold and all are clean and clear and not clogged up

that means you have to clean up carbon buildup and or start dooing at least a partial rebuild

anywhere from the fuel system to injectors to pumps

or valves, combustion chamber, pistons etc...

tolerances will get bigger as the engine wears

so a QUICK test is to add something like zddp additive by stp...and use a nice thicker oil than recomended

like someone else mentioned if this improves and decreases soot and exhaust smoke and smells, it will also quiet down the engine, it simply means your engine is a but tired in general terms and simply needs a rebuild



if you dont feel like doing this there are ways to clean up a bit without tearing apart but they arent always succesfull..

for example a high doseage in a full clean tank of fuel of SEAFOAM, under load at the dock or towing something for example, many times over can help to loosen deposits and stuff inside the engine

however the only real way of getting an engine back to specs is to get tolerances and parts back in new or original shape

bearings, pistons, rings, shims, valves, seats, flat surfaces, gaskets, o rings....etc etc etc...


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## jzk (Feb 25, 2008)

A quick search showed the max RPM of your engine to be 3600, and you are only able to get 3100. So why don't you start with the prop?



sandycohen said:


> Bubb - Sorry if I have gotten your bad side, not sure why you don't want to agree on anything that you seem to agree to.
> 
> For everyone else - an update:
> 
> ...


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## gamayun (Aug 20, 2009)

I think the OP and the most recent poster are separate. The latest question had been resurrected on an old post....


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