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Old 09-03-2013, 01:06 AM   #1
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Running at high RPM

I have often heard that a diesel engine needs to be opened up to full throttle every now and then to clear it all out, so to speak.

However my original Lehman manual clearly says that at high RPM you will get blue smoke from the exhaust, denoting unburned fuel.I would have thought that unburned fuel would be the last thing a diesel engine needs.

Any thoughts from the more mechanical forum members?
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Old 09-03-2013, 06:51 AM   #2
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Most small boat engines come from a light truck or farm implement source , not an industrial source.

Full throttle on these engines should be limited to a few minuets a year when checking the drive train.

There is no reason to : blow her nose: except to find out what the top RPM is so you can avoid overloading by operating 10% or 300RPM below that number.


Real industrial engines will have a 4 part load table chart and can be operated by Da Book 24/7/365 at its rating.
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Old 09-03-2013, 12:19 PM   #3
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Full throttle operation should be limited to what the manufacturer recommends.
Other engine speeds and loads should also be according to the specific engine manufacturer guidelines.

Top rpm should be rated hp rpm.

Different engines are rated by different standards.

Sounds like your Lehman manual was written by someone w an over propped boat.
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Old 09-03-2013, 04:21 PM   #4
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Quote:
Originally Posted by Andy G View Post
I have often heard that a diesel engine needs to be opened up to full throttle every now and then to clear it all out, so to speak.

However my original Lehman manual clearly says that at high RPM you will get blue smoke from the exhaust, denoting unburned fuel.I would have thought that unburned fuel would be the last thing a diesel engine needs.

Any thoughts from the more mechanical forum members?
Hmmmmm...always though unburnt fuel was white smoke and not enough air to thoroughly burn the fuel was black soot...

Blue usually means oil...

Colour of engine smoke and when it occurs tells about internal condition
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Old 09-10-2013, 02:10 PM   #5
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Bob Smith at American Diesel suggests that Lehmans be run for 5 minutes of WOT regularly to check the health of the cooling system and other peripherals. I seem to recall "monthly" but I refuse to commit to that number, I didn't write it down. The old clam-crusher makes such an unholy racket at (in my case 2500 rpm) that I was loathe to do it and certainly didn't stand over top of the engine when I did do it! The boat threw a very satisfactory but massive wake, though; sadly, I could never find a Sea Ray nor a Bayliner to rock while doing it.
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Old 09-10-2013, 02:28 PM   #6
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Welcome aboard Mr. X. Hmmm...has a nice ring to it.
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Old 09-10-2013, 03:54 PM   #7
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(XsBank-- Sent you a Private Message regarding high rpms and FL120s.)
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