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Old 10-02-2022, 06:37 AM   #1
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Diesel myths

These are admitedly pretty basic, but thought there might be 1 or 2 nuggets that some members could learn.

https://www.powerandmotoryacht.com/m...l-engine-myths
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Old 10-02-2022, 07:53 AM   #2
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Thanks for that. Very informative.
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Old 10-02-2022, 10:40 AM   #3
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I agree with the article and have done so for years.
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Old 10-02-2022, 11:31 AM   #4
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Old 10-02-2022, 12:30 PM   #5
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When I hear someone hit the throttle and then shut them off it makes me laugh.
The one that makes me cringe is when some start the engine with the throttle cracked and it immediately revs up and leave it there for a bit then idle it down. Where I’m at it’s amazing how many do it. Usually the ones that think that they have to start the engines on the coldest day of the year.
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Old 10-02-2022, 12:47 PM   #6
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I don't do any of that stuff either.
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Old 10-02-2022, 02:33 PM   #7
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That is how I run my engines.
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Old 10-02-2022, 03:08 PM   #8
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Old 10-02-2022, 03:47 PM   #9
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Originally Posted by RustyPBucket View Post
.
The one that makes me cringe is when some start the engine with the throttle cracked and it immediately revs up and leave it there for a bit then idle it down.
Gensets
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Old 10-02-2022, 03:50 PM   #10
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Gensets
Not sure what hits means. My genny is one speed always, but I give it a minute or 2 after start before I load it and the same when shutting down. Is that not correct?
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Old 10-02-2022, 03:59 PM   #11
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Originally Posted by RustyPBucket View Post
When I hear someone hit the throttle and then shut them off it makes me laugh.
The one that makes me cringe is when some start the engine with the throttle cracked and it immediately revs up and leave it there for a bit then idle it down. Where I’m at it’s amazing how many do it. Usually the ones that think that they have to start the engines on the coldest day of the year.
I wonder why then some land diesels throttle up to high idle right after start

Gensets are a good example that more than high idle but less than max power doesn't seem to kill them prematurely.

I admit that if a marine diesel starts well and idles well enough, I have never left them in a high idle. But then again, I bring them up to high idle or more within minutes after start while motoring away, but they are under some load.
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Old 10-02-2022, 04:03 PM   #12
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Not sure what hits means. My genny is one speed always, but I give it a minute or 2 after start before I load it and the same when shutting down. Is that not correct?
But I'm guessing when it starts it's running at a bloody high RPM, so for those few minutes she's got a scream up?

Ours is a 1500rpm model, would hate to have the ones that spin faster.
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Old 10-02-2022, 04:19 PM   #13
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For any boat engine I generally start it, confirm oil pressure, then bring it up to high idle (carbed gassers get started at high idle). Confirm water flow and start pulling dock lines. Once it's been running for a minute or 2 and I'm down to the last lines, throttle back to idle, confirm a stable idle, then drop the last lines and go.

The worst offenders I see for overly long warm ups are sailors. It seems like many of them don't trust engines and feel like the longer it runs, the more chance it'll stay running. I see plenty that start the engine before any other departure prep and leave it idling (rarely at high idle either) for 15 - 20+ minutes before leaving the slip.

Generator unavoidably goes right to 1800. A couple minutes with no load, then load it up (not too much all at once).
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Old 10-02-2022, 04:20 PM   #14
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Originally Posted by Simi 60 View Post
But I'm guessing when it starts it's running at a bloody high RPM, so for those few minutes she's got a scream up?

Ours is a 1500rpm model, would hate to have the ones that spin faster.
My genset is at a constant RPM, a high idle but I don't know the actual RPM, whether starting or under load. It never runs up to a high RPM.
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Old 10-02-2022, 04:24 PM   #15
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Originally Posted by rslifkin View Post
For any boat engine I generally start it, confirm oil pressure, then bring it up to high idle (carbed gassers get started at high idle). Confirm water flow and start pulling dock lines. Once it's been running for a minute or 2 and I'm down to the last lines, throttle back to idle, confirm a stable idle, then drop the last lines and go.

The worst offenders I see for overly long warm ups are sailors. It seems like many of them don't trust engines and feel like the longer it runs, the more chance it'll stay running. I see plenty that start the engine before any other departure prep and leave it idling (rarely at high idle either) for 15 - 20+ minutes before leaving the slip.
But the point is, for diesels, I don't think you want to bring it up to high idle after start. That was covered in the article.

My routine is to start the engine at lowest throttle position. After about a minute or 2, drop the dock lines and put in gear to get out of slip. Once in the channel gradually increase RPM and load, but low idle with switching in and out of gear is usually enough to get me out of my slip.
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Old 10-02-2022, 04:32 PM   #16
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But the point is, for diesels, I don't think you want to bring it up to high idle after start. That was covered in the article.

My routine is to start the engine at lowest throttle position. After about a minute or 2, drop the dock lines and put in gear to get out of slip. Once in the channel gradually increase RPM and load, but low idle with switching in and out of gear is usually enough to get me out of my slip.
High idle is only a few hundred rpm above idle. Around 1000 or so for many engines. Especially from a cold start, it'll build heat a little faster and will often lead to a better burn than you'll get at idle when cold. It's particularly noticeable on some diesels that smoke a bit after a cold start and don't clear up until you get a little heat in them.

You don't want too much rpm or load until it's warm, but you also want to get it warmed up quickly. That's why it's a waste to dawdle in the slip with it running for too long, it'll warm up much faster with a little load.
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Old 10-02-2022, 04:37 PM   #17
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High idle is only a few hundred rpm above idle. Around 1000 or so for many engines. Especially from a cold start, it'll build heat a little faster and will often lead to a better burn than you'll get at idle when cold. It's particularly noticeable on some diesels that smoke a bit after a cold start and don't clear up until you get a little heat in them.

You don't want too much rpm or load until it's warm, but you also want to get it warmed up quickly. That's why it's a waste to dawdle in the slip with it running for too long, it'll warm up much faster with a little load.
I agree, but I believe, a higher idle does little to warm up a diesel unless there is a load. So for me, I start at low idle and leave it there as I begin to leave the slip and get into the channel and then gradually increase RPM under load. I don't increase idle with no load. Probably doesn't make a big difference in the long run, but that's just my routine
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Old 10-02-2022, 04:41 PM   #18
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I agree, but I believe, a higher idle does little to warm up a diesel unless there is a load. So for me, I start at low idle and leave it there as I begin to leave the slip and get into the channel and then gradually increase RPM under load. I don't increase idle with no load. Probably doesn't make a big difference in the long run, but that's just my routine
Probably not a big difference. But I've always figured that if road vehicles raise the idle speed to get combustion temps up for long idle periods or for faster warmup, it should apply while I'm removing dock lines. I always pull power cords and such before startup, as I only want to see the engines run for a minute or so before I'm happy to go if it's got a good idle.
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Old 10-02-2022, 04:56 PM   #19
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My genset is at a constant RPM, a high idle but I don't know the actual RPM, whether starting or under load. It never runs up to a high RPM.
All gensets are at a constant RPM but....

Quote:

A 50Hz generator spins at 1,500-3,000 RPM, whereas a 60Hz spins at around 1,800-3,600 RPM
And

Quote:
Typically, a United States portable generator runs at 3600 RPM, with 2 poles, for a design frequency of 60Hz. Larger portable generators run at 1800 RPM with 4 poles here. That is how frequency is determined
A bit more than a high idle.
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Old 10-02-2022, 05:13 PM   #20
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All gensets are at a constant RPM but....



And



A bit more than a high idle.
Correct....

My genset ran at a higher RPM than my Lehman at cruise.

A lot of "experts" sound smart till you ask them why there are so many exceptions to their 'personal" rules or add a litle common sense to their advice.
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