Diesel Engine Minimum Run Time

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Vicarage

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Hi - several people I know have a habit of turning the engine on to get through a fluffed tack or out of irons, rag it to get the nose round, and then turn it off again.

I'm no diesel engineer, but is this likely to be killing the engine? Do Diesels have a minimum amount of time they should be run for once started, to allow everything to flow and warm up? Likewise, do they need to run for a period before they are given lots of load?

Ta
 
The rate of wear of engine components is greatest when the engine's cold. But there's no minimum time for running. People don't worry about starting their diesel cars for a few seconds to move them around the drive.
 
The odd short run does little harm. However it is important to run the engine under load for enough time (30-40 minutes) to get it hot at the start of a passage - not the common "just enough to get the sails up". overall modern small diesels are best run under a good load, typically between 2-2500 revs for reasonably long periods and periodically run for a few minutes at full revs. Engines die from over rather than underuse.
 
Vicarage said:
Hi - several people I know have a habit of turning the engine on to get through a fluffed tack or out of irons, rag it to get the nose round, and then turn it off again.

I'm no diesel engineer, but is this likely to be killing the engine? Do Diesels have a minimum amount of time they should be run for once started, to allow everything to flow and warm up? Likewise, do they need to run for a period before they are given lots of load?

Ta
Click to expand...

I know it's one of these throw away lines that only has a bit of truth in it, but I've heard it said that a diesel engine's life is measured in number of starts rather than hours of running.

However, I think if I were one of the people who have the habit you describe I'd be more worried about the cost of wear and tear on the sails that the engine. What's going wrong with their tacks?
 
"it is important to run the engine under load for enough time (30-40 minutes) to get it hot at the start of a passage"
Why at start of passage? And is the answer different if going on passage or short afternoon sail?
Thanks
 
When the sulphur content of fuels was higher it was recognised that running the engine for very short periods of time generated sulphuric and sulphurous acids (now officially sulfuric and sulfurous) that condensed on the bores of the engine. Corrosion occurred. If the engine was warm the majority of these inorganic acids went out with the exhaust gases. Nowadays this is far less of a problem.
 
srah1953 said:
"it is important to run the engine under load for enough time (30-40 minutes) to get it hot at the start of a passage"
Why at start of passage? And is the answer different if going on passage or short afternoon sail?
Thanks
Click to expand...

Luckily boat diesels are pretty thick. If you just whisper to it that it's the start of a passage, even when it isn't, it'll be happy.

Bottom lines:
try not to fire up a cold engine and only run it briefly. But sometimes, you may have to, in which case try not to become neurotic.
Engines are best warmed-up under light load. The best way of assuring this is to depart soon after starting it, then running on lightish loads until it's reached normal operating temperature. The best way to apply light loads is to set off; the worst way is to let it idle interminably whilst still berthed. This also avoids gassing your neighbours.
 
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I am not sure I agree with MacD.

I would certainly not run a diesel WOT immediately after starting, but after about a minute to warm up the combustion area, I'd go for a medium load working against the propellor as the quick way to up the core engine temp.

When everything is properly hot, then fulls revs against load for a while keeps a diesel happy and the bores and valves , and exhaust system, clean. That also gives the engine oil a chance to get fully warmed through and evaporate any moisture.


This is worth a read

https://www.azic.com/moisture-in-oils-the-three-headedbeast/.
 
So long as the calorifier is getting nicely hot, the engine will be doing the same.
When I had a seawater cooled engine, I used to change the oil more often.

I normally let the oil circulate a little before using more than a few RPM, especially if the motor's not been run for a while, but idling for more than 30 seconds is pointless. At idle, very little heat goes into the coolant, what little there is goes out the exhaust largely.
 
lpdsn said:
I know it's one of these throw away lines that only has a bit of truth in it, but I've heard it said that a diesel engine's life is measured in number of starts rather than hours of running.

However, I think if I were one of the people who have the habit you describe I'd be more worried about the cost of wear and tear on the sails that the engine. What's going wrong with their tacks?
Click to expand...

It's a big and heavy gaffer that needs momentum to get through the wind so short tacking up the river she'll stall and there's not the water to give her a second go!
 
Vicarage said:
It's a big and heavy gaffer that needs momentum to get through the wind so short tacking up the river she'll stall and there's not the water to give her a second go!
Click to expand...

I thought that sort of traditional boat used to be sailed with no engine at all.

Maybe it is the drag from the prop that is making the difference. :)
 
Here is a nice piece on marine diesels . spelling out the facts and myths , in terms I can even understandhttps://www.powerandmotoryacht.com/maintenance/diesel-engine-myths
 
Vicarage said:
Hi - several people I know have a habit of turning the engine on to get through a fluffed tack or out of irons, rag it to get the nose round, and then turn it off again.
Click to expand...

Agree that's abuse .
But its their engine (or maybe not ?).
 
a. I've got to believe some of the cold-running wear history is from vehicles that start under ACTUAL cold conditions. Very few of us boat well below freezing, and fewer below zero, yet trucks do that all the time.

b. None of this compares to leaving the engine sit for 9 months in the off season. How many here leave the engine unused for at least 4 months, thinking nothing of that?

And so this strikes me more as water cooler conversation than a real concern. More importantly, folks should learn how to tack.
 
thinwater said:
a. I've got to believe some of the cold-running wear history is from vehicles that start under ACTUAL cold conditions. Very few of us boat well below freezing, and fewer below zero, yet trucks do that all the time.

b. None of this compares to leaving the engine sit for 9 months in the off season. How many here leave the engine unused for at least 4 months, thinking nothing of that?

And so this strikes me more as water cooler conversation than a real concern. More importantly, folks should learn how to tack.
Click to expand...

Or if you're pushing the limits of short tacking, have the engine running?
Personally, one bad tack and I'd probably motor from there on.
 
sarabande said:
I am not sure I agree with MacD.

I would certainly not run a diesel WOT immediately after starting, but after about a minute to warm up the combustion area, I'd go for a medium load working against the propellor as the quick way to up the core engine temp.

When everything is properly hot, then fulls revs against load for a while keeps a diesel happy and the bores and valves , and exhaust system, clean. That also gives the engine oil a chance to get fully warmed through and evaporate any moisture.


This is worth a read

https://www.azic.com/moisture-in-oils-the-three-headedbeast/.
Click to expand...

Sarabande, your inbox is full.
 
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