Diesel myths

[backinblue]

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

https://www.powerandmotoryacht.com/maintenance/diesel-engine-myths

 

[2savage]

Thanks for that. Very informative.

 

[C lectric]

I agree with the article and have done so for years.

 

[SteveK]

 

[RustyPBucket]

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.

 

[Delta Riverat]

I don't do any of that stuff either.

 

[Comodave]

That is how I run my engines.

 

[Nomad Willy]

My two bits …
1. No
2. Yes
3. No
4. No

 

[Simi 60]

.
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

 

[backinblue]

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?

 

[psneeld]

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.

 

[Simi 60]

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.

 

[rslifkin]

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).

 

[backinblue]

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.

 

[backinblue]

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.

 

[rslifkin]

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.

 

[backinblue]

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

 

[rslifkin]

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.

 

[Simi 60]

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....

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

And

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.

 

[psneeld]

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.

 

[RustyPBucket]

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.

I looked up the definition of high idle: High idle means the highest engine speed obtainable when the engine is disengaged from the transmission and is free-wheeling.
No thanks. Not my engines.

When a genset has the switch disconnect off it doesn’t rev really high but the only ones I have experience with are the ones that are used in the oil patch. Are ones on boats different?

I was taught that any engine shouldn’t be revved up until the components have had a chance to warm because everything has different mass and by revving up cold, things haven’t had a chance to expand and there is a risk of damage. I’m old school and things have come a long ways since I started out. So when an engine has oil pressure I slowly bring it up to 1000 and give it a chance to warm up. Then put it to work under light load until operating temp is reached. If it’s not set up that way I guess the manufacturers know better I suppose.
A friend of mine who was a Finning tech until he retired once told me that starting an engine is one of hardest things on it.

Maybe with the advent of computer controlled systems one doesn’t have to be so diligent anymore.

 

[Simi 60]

Correct....

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

As does ours
Genset 1500
Main engine 1150 cruise

Can't imagine what 3600 sounds like

 

[rslifkin]

I looked up the definition of high idle: High idle means the highest engine speed obtainable when the engine is disengaged from the transmission and is free-wheeling.
No thanks. Not my engines.

I'd consider that as max governed rpm, not high idle. I've always heard high idle referred to as a slightly elevated idle like the 1000 rpm you mention (as opposed to normal idle or on some engines low idle).

 

[RustyPBucket]

I'd consider that as max governed rpm, not high idle. I've always heard high idle referred to as a slightly elevated idle like the 1000 rpm you mention (as opposed to normal idle or on some engines low idle).

I’m with you on this. In my minds eye I see things appearing on the outside the block that should be on the inside.

 

[psneeld]

Spend some time in commercial marine industry and see how engines that survive better than recreational ones are treated.... you might just be suprised what kills them or not.

 

[luna]

In Caterpillar speak, High Idle is WOT with no load, you are in neutral It's useful in determining if things are set reasonably well and if so, you should you reach the governed PRM limit. You don't linger there.

Reaching the governed RPM limit at WOT while under load is a whole different thing.

 

[Delta Riverat]

Captain told me to start at low, then advance until engines ran smooth. This was about 680 at start and 750 at "smooth"

Then check the water pumping, then go and release the dock power and all but one dock line and proceed. The last dock line released after backing up enough to do so.

There is at least a half mile of 5 MPH no wake zone and by then all is well.

 

[RustyPBucket]

Spend some time in commercial marine industry and see how engines that survive better than recreational ones are treated.... you might just be suprised what kills them or not.

I can only imagine.

 

[RustyPBucket]

In Caterpillar speak, High Idle is WOT with no load, you are in neutral It's useful in determining if things are set reasonably well and if so, you should you reach the governed PRM limit. You don't linger there.

Reaching the governed RPM limit at WOT while under load is a whole different thing.

When I first got Shy-Ann I did that one day at the dock determining what the governed speed was. Just before Happy Hour. One guy wanted to know if I wasn’t afraid of blowing it up.

 

[Art]

Gasoline engines are so simple to use and easy to work on; as well as inexpensive to care for... just saying!