Black water from 2gm exhaust

[never monday]

don't worry about what's coming out other than to make note and describe it. push the throttle full forward underway and let the RPM climb to what it will. Make a note of the max number and back off until the crud/smoke abates.

ps. move the lever with teh engine off and confirm you have full travel at the engine.

[Tempest245]

I might also give the impeller a check after a grounding like that..

[IslandHops]

I had a similar problem with a 3gm30f. Replaced exhaust mixing elbow and engine ran much better.

[James S]

If you were dogging the engine causing it to smoke...much of that black smoke may have simply accumulated in your water lock/lift causing the water to go black.

[Aquah0lic]

Well, I'm finally back in internet range and I have my magic #. It's 3200. At first there was a little smoke and then nothing. I ran that speed for 20 minutes. My top speed only went up .2 mph and the back of the boat was so buried, the exhaust pipe was just under water. Its usually about 8-10 in above. I also burnt about 1/4 of the dipstick range of oil over 2 days. I ran 2600 the rest of the time. Factoring fuel & oil use, negligable speed gain and drivetrain wear I think the more moderate 2400-2600 speed is were I'll be living. Is it a good idea to run in wide open every now and then to blow out the junk or is that myth?

[never monday]

I think you need to reprop. That engine should go 3600. This will also slow the boat down so she doesn't squat as much trying to climb the bow wave. Ideal fast cruise for that engine is 288-3200.
My guess is someone proped it to run at a lower RPM by over pitching it intentionally to get boat speed.

running it WAO is good for it. But no more than one hour out of 12.

[Aquah0lic]

Thanks so much for this great info but I can't see myself forking out the dough for a new prop right now so I'll have to live with it for a while.

Does my oil consumption seem excessive to you or do deisels normally burn some oil when your running all day?

[never monday]

you could repitch that one
do you know the specs on your prop?

how many hours of motoring was that oil consumption over?

[Aquah0lic]

I am in Oriental today and spoke a guy here that said exactly the same thing about being overpropped. He said I can get my 3 blade repitched locally for $75 or a new 2 blade prop for $200. I thought they were much more expensive. I don't know the specs on my prop but was told it is likely stock as Pearson is known for over-propping. I don't know if thats true.

The oil consumption was over approx 20 hours of motoring.

I ran at about 2900 for 3 hours this morning coming into Oriental and it ran fine and didn't squat too bad. I believe I'll deal with the prop until I haul out or get somewhere that I can dive it.

[never monday]

the oil consumption I would put on the high side of normal. With being over propped for years it's not unexpected.

[BassAckwards]

I believe it was Nigel Calder who stresses the importance of running the diesel under a load, at speed and for at least 45 minutes. He stated that not doing this will cause build up in the exhaust system to the point of creating a lot of back pressure, and thus damage to the engine. This buildup can collect throughout the exhaust system, hose and elbow.

Running the engine for 45 minutes allows the exhaust to reach a high enough temp to clear itself. I now hardly ever allow my engine to just sit at idle and feel that Calder's advice has merit.

[PaulM]

Before you go repitching the prop and any other "tuning " to reach 3600 rpm (no load) calibrate the rev meter. I found mine off by 600 rpm.

Paul

[never monday]

Originally Posted by PaulM

Before you go repitching the prop and any other "tuning " to reach 3600 rpm (no load) calibrate the rev meter. I found mine off by 600 rpm.

Paul

Yanmar tachs count flywheel teeth. They are far more accurate than a tach driven off of the alternator.

The factory sets the maximum no load speed. This should not be messed with.

[PaulM]

Thanks Never Monday. I agree, DON'T mess with the no load max RPM. The Yanmar tach may count teeth and be very robust, but mine was off never the less.

PaulM

[Aquah0lic]

I guess I'll just run it at maximum speed without squatting bad for extended periods and keep an eye on the oil until I can get my prop issue resolved. Thanks for all the direction, guys.