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op only you know if you have suffered performance

my 2gm would getb to hull speed easily on my 10k displacing old boat...

it was a 2 bladed prop btw...not even 3...

our typical cruising rpms was 2800, but if we wanted to sip fuel wed go down to 2200 or so...and still do 4-5 knots depending on what the sea was like...

like on motorcyles gearing can make a huge difference to engine performance so if you can Id try extreme opposite type props

like a low pitch 3 blader and a high pitch 2 blader...just to rule out the actual engine

ps its normal for engine to use oil of you are sort of abusing it...

while a quart at that throttle is a bit excessive many engines drink oil all the time NORMALLY

are you smoking a lot? do you get a sheen on the exhaust water?
 

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Not familiar with that engine, 20 HP? Maybe not enough power to swing a bigger prop? If you are running it close to max RPM's for long periods of time that may be why it is using some oil, or it may be a bit on the tired side? Was there any work recently done on the engine? Is the timing spot on? Injectors clean and up to spec? If you can run it that fast, it appears it is getting adequate fuel?

Any info on similar boat/motor combination, forums, owners clubs, etc?

Paul T
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this is gold info...part of the reason I didnt recomend doing wet tests per se here...they are usually for gas engines wiuth lower compressions and ease of testing...doesnt mean you cant do it though

basically even compression tests wont be really iluminating for the op here...

if the engine starts, doesnt sputter, has good fuel pump and injectors you either live with it(yes it might be a bit underpowered) or you tear it down and rering, deck and cleanup up the valves and tolerances

usually though if it AINT broke no need to go there

I would look into repropping better for the meantime

again is it smoking bad, or just losing oil at high rpms? oil loss at high rpms is a given in most engines...especially low reving ones...:)

anywhoo
 

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yeah I cant get an answer on the smoke thing...I have asked many times now...if you have a sheen on the water when really giving the engine some power that means you air blowing oil past the rings...if you are NOT, and ARENT smoking and your only 200-300 shy of max rpms

dont do anything to the engine...like minnewaska says tachs are notoriously innacurate and is not something to base all performance on best bet is get a good digital one...and do test run bypassing the panel one...

for example, is it an easy starter, is idle steady and smooth, smoke, yes no? vibrations, oil? etc all are indicators of good performance or not

also most old engines wont achieve max new rpms well cause they arent new..you cant expect and old engine like that to be in equal or better shape than new....

answer this first

smoke if yes what color?
if black is it just sooty or is there a sheen in the water?

is your fuel pump, diaphragm and all related pump hardware in tip top shape?

cheers
 

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it is slightly underpowered by todays standard

my reference point was an old stout wooden h28 displacing 10k pounds...full keel...
 

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BINGO there you have it!

this is what we were needing to know!

the sheen means blowby cause the rings arent exerting enough pressure on the liners/cylinders therefore letting oil blow by the rings...unburned...

the excessive soot when gunning it is indicative mostly of carbon buildup and soot in the valves, seats area...they dont seal properly...also more than likely major buildup on the piston tops...so every time you gun it a lot of it gets dislodged

a good way of checking on this is to run seafoom through the system many times...if you see an improvement it means you have masssive carbon buildup

if you also see an improvement using thicker oil and an oil additive like stp zddp...that also means your rings are tired...you can safely say now your initial low compression results are from this

it could also point to the fuel system hencee why I asked about condition of fuel pump, diaphragm etc...

Im assuming you have checked the air filter strainer right?

the white smoke after sitting or when cold could mean you have a slight gasket leak at the head or that youre heat exhanger is leaking a bit onto the valves or that its letting coolant backflow into the engine after sitting a while...

basically this is all indicative of a worn engine...

the good news is rebuilds arent that expensive especially if you do the work yourself and just get the machining done at any reputeable shop

the only expensive parts are the heat exhanger and making sure its not badly corroded inside.

the 2qm and 2gm engine rebuild kits go for around 700 in parts...

good luck
 

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he did say though that his exaust riser and elbows and all were clean so thats why you cant just rule out the smoke/soot

having said that my 2gm did it all the time and kept ticking like a clock...so yeah you can ignore it

the thing is with diesels you always have some fumes, soot, smells, etc cause diesel is damn dirty...

if it were a gas engine...soot just means you are either way too rich in the mixture and or you are passing unburned fuel trough the exhaust...

thats why its paramount to check your fuel system...

if everything checks, and EVERYTHING is in tip top shape and you are still having low power "symptoms" or desired performance than either you have to live with it, or you can do a simple rebuild

we are kind of reinventing the wheel here, honestly its simple...
 

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Christian, you mentioned on coolant leaks. I did notice coolant level in reserve tank dropping over time (a long time) its so small, i just ignore it. Its like drop by 1cm over 2-3years. Nothing to be concern I suppose? Or am I waiting for a big hit?
nope thats perfect...thats not your issue for sure...1 cm in 2-3 years...though is that the same coolant...?meaning you change only every 2-3 years?

I would change coolant every season but thats just me....or at least yearly

:)

well I guess I should ask how often do you use the engine...some things like gasket leaks arent really epxposed untill you have the engine real warmed up over a long period of time

might be fine for in and out but a "warped" head like minnewaska says will only be exposed after long running periods of time

but if your oil never gets milky its safe to rule that out for now
 

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well you can always send the oil to blackstone...

thats what my biker friends did...mostly to see what the fuel mix was doing to the oil and how long certain oils lasted in certain conditions

but for what they charge might as well put it towards a fresh rebuild

all engines need a rebuild after a certain period of time...its not a matter of if but when...

things like seals and orings, valve seals, etc all have a useable lifespan after that they fail...or crack or whatever

so just think of it that way

of course you can prolong the inevitable but someday it will need to be done unless you just plan to run this engine into the ground...take it off sell for parts and repower

thats not unheard of btw! jajaja
 

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do you use it every day? or every season?

the reason I say this is its quite possible that you do have a bad head gasket or whatever but since you never use the engine till its really hot and used you will never know

plenty of engines run around with leaks in the cooling passages, and smoke a bit then burn off, etc...

I had a truck with a cracked head...never used it till it got to full operating temp and just topped off every once in a while

until it finally cracked(the gasket completely blew) and I just soldered up the passages later on

what would a typical day of engine use be for you?

15 minutes out 15 minutes in?

1550 inst massive but it could be enough to warrant a rebuild cause it all depends on previous maintenance or lack thereof

it only takes running low on oil once or twice for you to be able to damage rod bearings and or pumps so hours alone wont tell you much
 

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your right minnewaska...absolutely but going by hours alone is useless...you dont know if it HAS been abused, or improperly maintained at any point

op are you the original owner? have you done all the maintenance on said engine?
 

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rebuild it...those 3 things you mention would make me do it at least

without getting into details I dont know why a new engine could get coked up and rusted so quickly

its possible right there that you damaged and pitted at the least exahaust valves

but you say you took it to a shop so it got fixed

cool

the low oil could damage rings if run for a while like that, you can also score the liners/cylinders as well causing you to burn oil...

the oil turning black quickly is common...however after only a couple of hours is a bit much in my opinion...

in any case...thats my recomendation

a quick well done refresh with a rebuild kit will also get you any lost power back, improve fuel consumption, noise, etc...etc...

good luck
 

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Back then, I was nursing a brand new engine initially. Running on low rpm mostly. Didn't know diesel engine loves S&M that much. ;)
gotcha

its easy to coke up, now the rust? why? you not have a good waterlift or you got heavy seas backing into the engine or what?:)
 

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ok just normal use then

ok well I think you have options on what to do...some of your issues we now can assume were caused by the things you just mentioned...

the low oil is what I most am concerned about...simply put it could be the cause if scored cylinders...do you hear slap or knockingwhen starting up?

this in turn causes lose tolerances so the rings get lose...once they losen up beyond a certain point the lands are way too apart...and you can get oil passing by and not sealing well

honestly its not a deal breaker

use thicker oil, stp and call it a day or prep for a rebuild

it doesnt seem you have any issues with the heat exchanger, coolant etc but in a rebuild something will always show up, be it a slight passage clogged up or a little tear in the gasket...etc...
 

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exactly you can alleviate a lot of the strain the engine is currently having by lowering pitch(after you try a high pitch one to bog it down and know where) therefore allowing the engine to gain a bit more torque, also you might increase your cruising revs up

but hear me out, you will not gain speed...you will gain torque...meaning the engine will improve the torque it has usually in midrange or cruising rpms and slow manueviring, in most cases you lose topspeed but gain considerable rpms where you need it...

this will alleviate the engine a bit and not load it up to where its fighting to keep up rpms

its a good choice since the engine is a bit tired but by no means trash...

dabins posted a good question

whats your oil pressure? do you even have a gauge? not just the idiot light yanmars come with?

you can learn a lot from how tired an engine is by simply looking at oil pressure at startup and then how it lowers when warmed up...if its drastically lower in normal range again you can experiment with stp, thicker grade oil and the like as it will tighten up tolerances a bit and thats that

a good way to prolong the rebuild...

cheers
 

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yeah guys agree...

hope any and all of this talk actually helps the op some!
 

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to me its a testament

you actually arent NOT getting to max rpms...

my 2gm showd the same resiliency even after clogging injectors with sea water when refuelling at sea...

or getting partially submerged after my bilge pumps stopped working ana drained the batteries or countless hours of abuse in choppy seas...

use the prop that gets you to 3400, if I remember correctlt I never went over 3500rpms...maybe once before leaving on the cruise...

6p isnt that bad... and it willkeep your engine happy and not bogged down

like minnewaska says you have been overpropped more than a few times now...(after testing the 9 pitch prop what prop did you leaveon there for the last 5 years?)

just get the prop that gets you 3400 and your are good to go

prolong the rebuild, you dont NEED it

get thick oil...stp in the oil and call it a day

also and this is just me...always use a fuel stabilizer, or even seafoam or similar that just keeps the fuel clean...this is of course if your tank is clean if not its a waste of money...

seafoam does wonders in cleaning up the small fuel passaged but also does wonders in unclogging injectors over time...

a strong mix of seafoam over a couple of tank fulls of new gas will make an improvement beleive it or not...it also acts as a stabilizer for long periods of time

having said that I once left my small 10 galon diesel tank half empty for over a year only using the engine to charge the batteries once every month or so...and the little yanmar had no issues whatsoever...

anyways

just live with the fact that you can麓t get the desired top speed you might of once had

thats just normal but hardly a reason to tear down an engine

if it aint REAL broke dont fix it...
 
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