Any Harm Short Running Diesel Engines

[gottaluvit]

I hope I am asking this in the right forum but I have two MVs this question pertains to. I have never owned a diesel engine and within the last four months, I am an owner of two. I hate to hear an engine sit idling needlessly and at low oil pressure, so I have always shut gas engines off even if I only ran it 30 seconds or so to move it just a few feet. I have done the same a few times with the 6.2 in the CUCV as well as just a minute or so to raise or lower the bed in the 8.3 in the M929 dump. Do these short run times hurt a diesel or is it ok?

Thanks in advance,
Jim.

 

[MtnSnow]

Short term and the occasional short run really won't kill the motors but a constant habit of short running will increase wear long term. Short running in cold weather is much harder on the motors as they end up building enough heat to draw in cold moisture laden air but don't get hot enough for a long enough duration to burn off that moisture. Truthfully short running will be harder on the batteries as they will not keep the batteries fully charged/topped off with short runs

 

[61sleepercab]

Most engine wear is at start up when no or low oil pressure at bearings. Short runs without coming up to operating temperature is **** on oil as water does not boil off. A local funeral home car once had to have the oil pan heated before the oil would run out of the oil drain. Short trips are usually classified as Severe Duty requiring extra maintenance. I run vehicles who set a lot up to temperature every 3 or 4 weeks . I would not get into habit of short running as fuel is cheaper than motor parts. Mark

 

[Valence]

Short term and the occasional short run really won't kill the motors but a constant habit of short running will increase wear long term. Short running in cold weather is much harder on the motors as they end up building enough heat to draw in cold moisture laden air but don't get hot enough for a long enough duration to burn off that moisture. Truthfully short running will be harder on the batteries as they will not keep the batteries fully charged/topped off with short runs

Excellent point about the batteries!

One comment though, warm air will hold more moisture than cold air (it's why Antarctica is actually the driest place on earth). Also, to create condensation that you're describing you need warm air hitting a colder object. When the temperature of the air passes its dew point, that's when water will condense.

But of course, you're still 100% correct about the results. The engine (and many related parts) will still be cold but have warm exhaust - with additional water by-product from the combustion - and the water will condense and collect until the engine & component temperatures are raised to evaporate the water.

You can see this on cold operating cars in front of you at a stop lights. When the light turns green and they start accelerating water will drip out of the exhaust pipe end. That's water condensing on colder exhaust parts. Of course, this is rather bad on mufflers too.

 

[Katavic918]

When I drive my M35A2 I let it run even if I have to go into a store for up to 10 minutes. I pull the throttle trim out in order to boost oil pressure and smooth engine vibration. Not sure if you have this ability in you vehicles.

 

[FloridaAKM]

This is exactly how I drive my Deuce, never short running it for any reason, due to condensation in the system. I have a friend who is a mechanic who drives his Deuce to the coffee shop every (Saturday & Sunday) morning, which is a mile or two from his house. I've tried to explain what he is doing to the engine, but he tells me I worry too much.....

When I drive my M35A2 I let it run even if I have to go into a store for up to 10 minutes. I pull the throttle trim out in order to boost oil pressure and smooth engine vibration. Not sure if you have this ability in you vehicles.

 

[gottaluvit]

Ok. From what you all have said, condensation is my enemy and it's not a diesel specific issue, right? So if it's already a warm engine it is fine, but a bad thing to do to a cold engine. Using that theory, I suppose I shouldn't short-run cold gasoline engines either. Thank you all. I guess I will just have to get over being so annoyed by an idling engine.

 

[wrenchturner6238]

There is one thing to think about on your 8.3 it has a turbo. It is advisable to at least let the turbo cool off before shutting down if you have been in a hard pull . A few factors figure in though slower driving after a pull ( like driving through town a little or down the dirt road) If you are pulling hard let it idle a little before shutting down.

 

[gottaluvit]

There is one thing to think about on your 8.3 it has a turbo. It is advisable to at least let the turbo cool off before shutting down if you have been in a hard pull . A few factors figure in though slower driving after a pull ( like driving through town a little or down the dirt road) If you are pulling hard let it idle a little before shutting down.

Thank you. I have kept the turbo issue in mind as I have a vw turbo and dealership mechanic told me about that as I was there getting an oil filter one day. I, also considered just easy driving enough to cool the turbo, rather than just idling, when feasable.

 

[Valence]

There is one thing to think about on your 8.3 it has a turbo. It is advisable to at least let the turbo cool off before shutting down if you have been in a hard pull . A few factors figure in though slower driving after a pull ( like driving through town a little or down the dirt road) If you are pulling hard let it idle a little before shutting down.

You are correct on both accounts that short running gas and diesel engines is bad on them both.

The issue that's more diesel specific is running a diesel engine for a long time with little or no load. Diesels generally are much slower to warm up than gasoline engines and can cause "wet stacking". Wet stacking is unburned fuel collecting in the exhaust side of the turbocharger and then on to the rest of the exhaust system.

I like this quote from Wikipedia:
https://en.wikipedia.org/wiki/Wet_stacking

"It is detectable when there is a black ooze around exhaust pipe connections and around the turbocharger. Continuous black exhaust from the stack when under a constant load is also an indication that all the fuel is not being burned."

 

[Valence]

There is one thing to think about on your 8.3 it has a turbo. It is advisable to at least let the turbo cool off before shutting down if you have been in a hard pull . A few factors figure in though slower driving after a pull ( like driving through town a little or down the dirt road) If you are pulling hard let it idle a little before shutting down.

I second this as also very true. Even my M35A2 has a warning plate about idling for 5 minutes to allow the turbocharger to cool down.

 

[wrenchturner6238]

Valence
You are correct this wet stacking is caused from to much idle (most of the time) making the pistons / rings shrink from being to cool for to long and not burning all the fuel fully from low compression.

 

[frank8003]

Tactical military vehicles are built for a purpose {to get the job done}.
Built to run as long as one can get fuel into them.
They are not built like Hondas, Toyotas and such.
It is not a Chevy either.................
Were built to come up to temperature and normalize/maintain
temperatures and internals at the engineered clearances.
Can run, shut down, run, at specific intervals depending on how fast
the internals change sizes due to temperature.
One would not want failed equipment due to frugality.
Remember
"Always measure what you might gain against what you might loose"

 

[gottaluvit]

Tactical military vehicles are built for a purpose {to get the job done}.
Built to run as long as one can get fuel into them.
They are not built like Hondas, Toyotas and such.
It is not a Chevy either.................
Were built to come up to temperature and normalize/maintain
temperatures and internals at the engineered clearances.
Can run, shut down, run, at specific intervals depending on how fast
the internals change sizes due to temperature.
One would not want failed equipment due to frugality.
Remember
"Always measure what you might gain against what you might loose"

You most likely hit the nail on the head on the frugality. Up til the last seven years I had been running such a tight budget that ten dollars would have been the difference in making the bills or not. Could be ingrained and now it's a subconcious thing. These diesels both are fuel sippers anyway. 14 mpg in the CUCV and 10 mpg (working) in the M929. I can't complain since the '86 civy truck only got 8 mpg.

 

[dmetalmiki]

Interesting thing about this over here (U.K.) delivery and post vans leave engines running whilst hopping in and out at short stops. But it is against the law to leave a vehicle with the engine still running. No one seems to comply, and no prosecutions that I know of. P.S. All that water coming out of the exhaust pipe is a result of the actual combustion process itself.

 

[Speedwoble]

Here's my take. If you have to start an engine just for a bit, it is still better to shut it off after it is done than to let it sit there and idle. I.E. if you just have to start your 929 for 30 seconds to raise the bed, letting it idle is not going to undo the tiny amount of wear from the 30 seconds. And letting it run longer than needed is just causing additional wear. It is not needed for the turbo either because the turbo has not heated up in that slight load or short time.

Idling is harder on any engine because there is not enough combustion pressure to seat the rings, and there is not enough temperature to keep the combustion products from condensing in the oil.

So if you only need to do something for a short time, shut it down when you are done. If you need to do two 30 second duties, 1 minute apart, keep it running in between. But if it is two 30 second duties 10 minutes apart, shut it down. And if you are doing a bunch of short stuff, change your oil often.

 

[gottaluvit]

Here's my take. If you have to start an engine just for a bit, it is still better to shut it off after it is done than to let it sit there and idle. I.E. if you just have to start your 929 for 30 seconds to raise the bed, letting it idle is not going to undo the tiny amount of wear from the 30 seconds. And letting it run longer than needed is just causing additional wear. It is not needed for the turbo either because the turbo has not heated up in that slight load or short time.

Idling is harder on any engine because there is not enough combustion pressure to seat the rings, and there is not enough temperature to keep the combustion products from condensing in the oil.

So if you only need to do something for a short time, shut it down when you are done. If you need to do two 30 second duties, 1 minute apart, keep it running in between. But if it is two 30 second duties 10 minutes apart, shut it down. And if you are doing a bunch of short stuff, change your oil often.

Thats how I always looked at it with my gas engines, but wondered if diesels were needing to run longer since I see so many 18 wheelers left idling and thanks for reminder on oil changes. Is it every 3000 miles if short runs and dusty environment? I rarely see 50 mph.