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Old 10-07-2007, 03:51   #16
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I had the top end valvles) of our 1985 Volvo Penta MD17D rebuilt last year. The excellent mechanic said that the lower end... rings were the cause of the grey smoke at start up. First time in the spring is rather smokey!

In my case the smoke stops or becomes almost invisible when the engine get to operating temperature. There is almost no smoke when we start a warm engine, and none when we restart the engine which is at operating temperature.

We do see steam occassionally especially when the air is cool. It is not white smoke as it disappates quickly.

I suspect your grey smoke is from rings or cylinder wall glazing as noted above... and probably subsides when the engine heats up.

I don't know that I would do the rings on this 22 yr old engine. I will tolerate the smoke as long as it performs well in all other aspects. It does.

sv shiva

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Old 10-07-2007, 03:57   #17
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80% of max RPMS is cruising RPMS? I believe the design spec for my engine max is 3000, but I can't quite get there. I normally motor at 2,000± which in relatively calm seas and a clean bottom gets me close to hull speed (+7knots)... and I would have to go higher to make speed when condtions worsen.. headwind or some sea running.

I suspect that full efficiency my be best below 2000 in my case. What is the relationship to hull speed and fuel eficiency and RPMs... if there is one?

Does heeling have any impact on a running diesel?

sv shiva

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Old 10-07-2007, 04:39   #18
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Yes, my engine smokes upon startup but it goes away as operating temperature is reached. If re-started at operating temperature then there is no smoke or very very little. If restarted warm it smokes then goes away. There is no noticeable oil or coolant consumption and the engine starts very easily. But my engine was overhauled, new valves, pistons, rings, liners etc.....I am going to reconnect the glow plug and also follow Alans' instructions on glazing and see what happens.
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Old 10-07-2007, 05:37   #19
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The inability to reach cruising RPMs is often a result of over-propping.
Often, the best compromise cruising RPM, for a given boat/engine/propeller combination is to accelerate until black smoke just appears, then reduce ‘till it disappears. This is close to your best RPM, as installed.
Another good indicator is to run the engine at that RPM that generates the specified operating temperature (often 180 deg. F).

Diesel and Propeller Tutorial ~ by Bob McCullough
C36IA - Diesel and Propeller Tutorial

Avoiding Diesel Engine Overload ~ By James Hamilton and Jennifer Hamilton
Avoiding Diesel Engine Overload

Propeller Sizing - Have You got the Correct Propeller? ~ by Robert Olds
Propeller Sizing - Have You got the Correct Propeller?
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"If you didn't have the time or money to do it right in the first place, when will you get the time/$ to fix it?"

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Old 10-07-2007, 12:49   #20
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Out of gear, rev your engine to max and take note of the RPM. Now place in gear and do the same again. The difference in RPM should be around and no greater than 10%. This would give a good indication that the boat is correctly prop'd. If you are over prop'd, you will use excessive fuel to distance covered and it is hard on the engine. Under prop'd also results in poor fuel economy. Properly prop'd results in your best economy and best load to power curves of engine. The boat will be more reponsive, especially in tight manouvering conditions were you need start stop ability. The boat will also tend to get up to speed better and you get better headway through sea and weather. Of course, all this depends ont he engien being capable in the first place.

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Old 10-07-2007, 14:57   #21
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I also agree with Alan. Engines designed with glow plugs start better with glow plugs. The white smoke is usually exactly what Alan mentioned, caused by not using the glow plugs to initiate a complete firing of all cylinders. The only time I don't use them is when the engine is hot from running. Good luck

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