Diesel Idling

[Mopar73]

So there I was at one of my local gas stations putting gas in my car and at the pump across from me had a old beat up Chevy 2500 diesel Idling away with nobody inside. Being a Chevy my first thought was the guy was afraid it wouldn’t start again so he left it running. Lol. When the gentleman came out of the gas station back to his truck I teased him about it not being able to start again. He assured me that it would start again and then said that it’s harder on the diesel engines to shut them off and start them back up. I gave him the puzzled look and said that that was an old wives tale from way back. He really seemed to think that it was still true.
My father used to be an over the road truck driver and I do remember him talking about that for the semi‘s and transport category diesels, but that was 30 years ago. I would have thought by now that a modern Cummins or equivalent would not have to do that.
So my question really is do you guys let your diesel trucks idle if you’re going to be gone for more than a few minutes. The guy with the Chevy was gone at least 10 minutes with it running.

 

[crash68]

part of why you leave a diesel idle when working them hard is to cool the turbo and engine down before turning the engine off. Unlike a gasser diesel cool off while idling. Synthetic oil will tolerate higher temperatures but it doesn't hurt to let it cool off some.
I usually draw the idle time at about 5 minutes, if it's going to be longer than that I shut the truck down. Long idling times does add to the soot loading of the DPF, likely hood of idling causing a problem is really slim.

 

[WY-Dave]

From the '18 diesel supplement (With DEF)

As usual, they use generic terms "Long periods of idle", turbo temp "cool warm hot"


for shut down

 

[GTyankee]

I can only tell you what i know from what diesel mechanics have told me.

Idling an diesel engine causes Carbon Build Up
Carbon build up is not at all good for the engine

Detroit Diesels are built differently than other diesels, because after you idle it for periods of time, then start down the highway,it blows the carbon right out the stacks.
No other diesel had that ability to blow out the carbon.

Any diesel that has been worked hard & has not had time to cool down is also bad, but not only for the diesel engine
It is even harder on the TURBO(s)
As the engine is being worked at any RPM, the turbo is spinning at a high rate of speed.
The inside of the turbo is made of thin blades. These blades are constantly being kept cool by a liquid being squirted on them.

Big trucks have a Pyrometer that indicates the heat level of the Turbo

When truckers pull into the place that they will be spending a couple hours or more, they don't shut off the engine for a while before shutting the engine off, they are waiting for the turbo temp to drop from something like 5 or 6 down to 3 or a time period of 3 minutes or a bit more

The reason for that rule is because the liquid only sprays onto the blades of the turbo while the engine is running.

Shutting off the engine causes that liquid pump to shut off & the hot turbo blades begin to deteriorate quickly without the liquid cooling them down.

What i can't say is, if the Ram Cummins diesels have that cooling
necessity

The next time that you happen to stop at a Truck Stop for what ever reason.
Look over at the trucks diesel isle, it is likely that you will see a sign over there that mentions the 3 Minute rule

 

[crash68]

Any diesel that has been worked hard & has not had time to cool down is also bad, but not only for the diesel engine
It is even harder on the TURBO(s)
As the engine is being worked at any RPM, the turbo is spinning at a high rate of speed.
The inside of the turbo is made of thin blades. These blades are constantly being kept cool by a liquid being squirted on them.

Big trucks have a Pyrometer that indicates the heat level of the Turbo

When truckers pull into the place that they will be spending a couple hours or more, they don't shut off the engine for a while before shutting the engine off, they are waiting for the turbo temp to drop from something like 5 or 6 down to 3 or a time period of 3 minutes or a bit more

The reason for that rule is because the liquid only sprays onto the blades of the turbo while the engine is running.

Shutting off the engine causes that liquid pump to shut off & the hot turbo blades begin to deteriorate quickly without the liquid cooling them down.

What i can't say is, if the Ram Cummins diesels have that cooling
necessity

Not sure where you came up with this but nothing get sprayed on turbo blades to cool them, water cooled turbos have a water jacket around the bearing area. Oil is also pumped through the bearings to cool them. A water/methanol spray is used on the intake system but it's not for cooling the turbo blades, it helps lower the air temp from the turbo going into the engine.
You watch the pre-turbo EGT during normal driving it somewhere in the 600°- 800° but that will climb upwards of a 1000° when pulling a trailer. The turbo in my EcoD exhaust side of the turbo can run into the 1500° but the engine management will back things off before then, Cummins has similar safeguards.

 

[chri5k]

I can only tell you what i know from what diesel mechanics have told me.

Idling an diesel engine causes Carbon Build Up
Carbon build up is not at all good for the engine

Detroit Diesels are built differently than other diesels, because after you idle it for periods of time, then start down the highway,it blows the carbon right out the stacks.
No other diesel had that ability to blow out the carbon.

Any diesel that has been worked hard & has not had time to cool down is also bad, but not only for the diesel engine
It is even harder on the TURBO(s)
As the engine is being worked at any RPM, the turbo is spinning at a high rate of speed.
The inside of the turbo is made of thin blades. These blades are constantly being kept cool by a liquid being squirted on them.

Big trucks have a Pyrometer that indicates the heat level of the Turbo

When truckers pull into the place that they will be spending a couple hours or more, they don't shut off the engine for a while before shutting the engine off, they are waiting for the turbo temp to drop from something like 5 or 6 down to 3 or a time period of 3 minutes or a bit more

The reason for that rule is because the liquid only sprays onto the blades of the turbo while the engine is running.

Shutting off the engine causes that liquid pump to shut off & the hot turbo blades begin to deteriorate quickly without the liquid cooling them down.

What i can't say is, if the Ram Cummins diesels have that cooling
necessity

The next time that you happen to stop at a Truck Stop for what ever reason.
Look over at the trucks diesel isle, it is likely that you will see a sign over there that mentions the 3 Minute rule

I rebuilt diesel engines for mining equipment for several years at a machine shop. Worked on Detroit's, CAT's, Perkins, etc. They all looked pretty much the same inside. Nothing special in a Detroit to "blow the carbon right out of the stack".

 

[SouthTexan]

I can only tell you what i know from what diesel mechanics have told me.

Idling an diesel engine causes Carbon Build Up
Carbon build up is not at all good for the engine

Detroit Diesels are built differently than other diesels, because after you idle it for periods of time, then start down the highway,it blows the carbon right out the stacks.
No other diesel had that ability to blow out the carbon.

Any diesel that has been worked hard & has not had time to cool down is also bad, but not only for the diesel engine
It is even harder on the TURBO(s)
As the engine is being worked at any RPM, the turbo is spinning at a high rate of speed.
The inside of the turbo is made of thin blades. These blades are constantly being kept cool by a liquid being squirted on them.

Big trucks have a Pyrometer that indicates the heat level of the Turbo

When truckers pull into the place that they will be spending a couple hours or more, they don't shut off the engine for a while before shutting the engine off, they are waiting for the turbo temp to drop from something like 5 or 6 down to 3 or a time period of 3 minutes or a bit more

The reason for that rule is because the liquid only sprays onto the blades of the turbo while the engine is running.

Shutting off the engine causes that liquid pump to shut off & the hot turbo blades begin to deteriorate quickly without the liquid cooling them down.

What i can't say is, if the Ram Cummins diesels have that cooling
necessity

The next time that you happen to stop at a Truck Stop for what ever reason.
Look over at the trucks diesel isle, it is likely that you will see a sign over there that mentions the 3 Minute rule

Sorry, but not one thing in this post is true.

Old Detroit's were dirty in general, and the black smoke coming out of those stacks was unburnt fuel. All old diesel engines did this, not just Detroit.

There is no type of coolant cooling down the turbo blades in the diesel engine in question or any diesel for that matter. The Cummins does have coolant going to the turbo, but that is to keep the VG actuator cool. Some turbos use thermal syphoning which pulls in coolant (even when the engine is off) to cool down the turbo shaft to keep oil from coking on the shaft.

Oil coking on the turbo shaft is the reason why turbos driven engines(not just diesels) may need to idle for a period after hard use and the turbo is hot. The shaft that holds the blades is fed with engine oil to keep it lubricated. If you turn it off after hard use, the heat will heat soak into the center of the turbo causing the oil to basically cook on the shaft.

OP, diesels generally don't use as much fuel when idling as gas engines. On older pre-emissions diesels, idling was not that much of an issue if the outside temp was not too cold to keep from wet stacking, however, with today's emissions equipped diesels idling has negative effects on emissions systems. I generally idle if it is really hot or really cold outside to keep the cab warm.

I also will idle if I need to make a stop(like a convenience store) and the engine oil has not got up to operating temp yet. I would rather idle than put my engine through another cold oil start which creates a lot of wear. In fact, most engine wear is due to the first 10-15 minutes after a cold start because your engine oil is not hot and thin enough to properly coat the entire engine especially in a diesel running 15w40.

 

[2003F350]

So when I had diesels, if I were running empty and going to head into a store for a while, I'd shut it down right away. Frankly, I would shut it down if I were walking away from it for any length of time and no one else was in the truck.

If I were pulling something (camper, decent load, etc), when I came to a stop (aka for fuel, food, or my destination) I would let it idle for 5 minutes or so, just to let things cool down some. Then it would get shut down.

From what I've gathered, most semis you see idling in a parking lot are either warming up, cooling down, or running because they need temperature controls while they're taking a break.

 

[Mopar73]

I just love a spirited discussion. I was a mechanic in my past life, so I completely understand how the turbo works and I totally agree that the turbo needs to be cooled down for a couple minutes after it’s been worked hard. Not really sure on the need to idle after normal driving, especially when you look around at all the gas vehicles with turbos that don’t seem to have any problems.
Besides the possible turbo cool down or just wanting to initially warm up the engine is there really any logical reasons to let it idle. And if somebody throws out starter wear and tear I’ll mediately call BS on it. Just watch a UPS delivery driver. 200 stops a day and A start each time. I don’t think they do it as a company if it was an issue


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[2003F350]

I just love a spirited discussion. I was a mechanic in my past life, so I completely understand how the turbo works and I totally agree that the turbo needs to be cooled down for a couple minutes after it’s been worked hard. Not really sure on the need to idle after normal driving, especially when you look around at all the gas vehicles with turbos that don’t seem to have any problems.
Besides the possible turbo cool down or just wanting to initially warm up the engine is there really any logical reasons to let it idle. And if somebody throws out starter wear and tear I’ll mediately call BS on it. Just watch a UPS delivery driver. 200 stops a day and A start each time. I don’t think they do it as a company if it was an issue


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This is something I've been saying about the auto start/stop feature on newer vehicles. I don't particularly care for the system because it can cause issues when trying to squeeze into traffic (having to wait for the motor to start again), but 1. it can be turned off with the push of a button and 2. it's NOT going to cause your starter to wear out prematurely unless there were already bad components in it, because its design was tested to last at least 100k miles in the worst-case scenario.

 

[SouthTexan]

I don't think there will be many logical reasons other than those that have already been stated. Although I would have to ask why it would matter if someone else is paying for the fuel? If it is due to emissions concerns, diesel emits less CO and CO2(greenhouse gases) than their gas counterparts and the gas counterpart would also use considerably more gallons of fuel than diesel would over the course of their life cycle even with many more idle hours on the diesel. Diesels do emit more PM and NOx, but the new emissions equipment drops these down to near zero.

EDIT: Doing the math on the combined fuel mileage of both on Fuelly with gas version averaging 12 mpg and the Cummins averaging 15.5, that would come out to 8,333 gallons used for the gas trucks and 6,452 gallons for the diesel trucks over 100k miles. Given that roughly .4 gallons of diesel is used for every 1-hour idling on the 6.7L, the Cummins would have to idle for about 4,705 hours over those 100k miles to equal the 8,333 gallons used by the gas truck according to the averages on Fuelly.

 

[Mopar73]

What really brought up the topic was where the truck was positioned and where I was fueling the exhaust was going directly at me with the breeze. Just kind of irritating for no reason


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[SouthTexan]

What really brought up the topic was where the truck was positioned and where I was fueling the exhaust was going directly at me with the breeze. Just kind of irritating for no reason


Sent from my iPad using Tapatalk

If it had emissions equipment, then you shouldn't have been able to smell much of anything and there would hardly be any PM or NOx coming out of the tailpipe. If it had its emissions system deleted, then it would not smell much different than a direct-injected gas engine of the same size, but with much less carbon monoxide(CO) since diesel emit much less than gas engines even without emissions equipment. These much higher concentrations of CO from a gas engine is what makes them lethal in a short amount of time. It would take you forever to get a fatal concentration of CO from a similar-sized diesel in a confined area.

Diesel exhaust(without emissions equipment) is bad for you with constant long-term exposure (as in years) due to PM and will not do much to you in the short term even if you breathed in a huge cloud of black smoke. Gas engines are way more lethal to you in the short term although many do not think about it because the exhaust cannot be seen. In fact, new direct-injected engines are putting out up to 10 times more PM than today's diesel yet nobody cares because you can't see it.

 

[GTyankee]

I misunderstood the diesel mechanics about the cooling off of the Turbo, from what you are saying.

Your explanation sounds more logical
'water cooled turbos have a water jacket around the bearing area. Oil is also pumped through the bearings to cool them'

I drove a semi trucks & worked Heavy Equipment from 1973 - 2003
Some gas powered, but mostly diesels

When i stepped out of semis for the last time,
There was hardly any emissions & most of the trucks had Fuller & Road Ranger Transmissions
They had 10 - 15 manual shift gearing.
After you got rolling, you shifted into a higher gear at 1750 RPM range.

Todays semi are so much different now
Some semi trucks are not allowed into California, because of emissions standards not being met

 

[Justin Stafford]

I can only tell you what i know from what diesel mechanics have told me.

Idling an diesel engine causes Carbon Build Up
Carbon build up is not at all good for the engine

Detroit Diesels are built differently than other diesels, because after you idle it for periods of time, then start down the highway,it blows the carbon right out the stacks.
No other diesel had that ability to blow out the carbon.

Any diesel that has been worked hard & has not had time to cool down is also bad, but not only for the diesel engine
It is even harder on the TURBO(s)
As the engine is being worked at any RPM, the turbo is spinning at a high rate of speed.
The inside of the turbo is made of thin blades. These blades are constantly being kept cool by a liquid being squirted on them.

Big trucks have a Pyrometer that indicates the heat level of the Turbo

When truckers pull into the place that they will be spending a couple hours or more, they don't shut off the engine for a while before shutting the engine off, they are waiting for the turbo temp to drop from something like 5 or 6 down to 3 or a time period of 3 minutes or a bit more

The reason for that rule is because the liquid only sprays onto the blades of the turbo while the engine is running.

Shutting off the engine causes that liquid pump to shut off & the hot turbo blades begin to deteriorate quickly without the liquid cooling them down.

What i can't say is, if the Ram Cummins diesels have that cooling
necessity

The next time that you happen to stop at a Truck Stop for what ever reason.
Look over at the trucks diesel isle, it is likely that you will see a sign over there that mentions the 3 Minute rule

Idle times are government rules not trucker rules. **** that. I let my rig run from the moment I fire her up in the morning till I shut her down at night. Could be a 15 hour day some days.

 

[Justin Stafford]

So there I was at one of my local gas stations putting gas in my car and at the pump across from me had a old beat up Chevy 2500 diesel Idling away with nobody inside. Being a Chevy my first thought was the guy was afraid it wouldn’t start again so he left it running. Lol. When the gentleman came out of the gas station back to his truck I teased him about it not being able to start again. He assured me that it would start again and then said that it’s harder on the diesel engines to shut them off and start them back up. I gave him the puzzled look and said that that was an old wives tale from way back. He really seemed to think that it was still true.
My father used to be an over the road truck driver and I do remember him talking about that for the semi‘s and transport category diesels, but that was 30 years ago. I would have thought by now that a modern Cummins or equivalent would not have to do that.
So my question really is do you guys let your diesel trucks idle if you’re going to be gone for more than a few minutes. The guy with the Chevy was gone at least 10 minutes with it running.

Yep sure do let it run if I'm only running into the convince store for 30 seconds.. 10 minutes or longer I'll shut it off and command start it

 

[Timsdually]

I don't idle.

Cylinder Wash.

 

[TrailRider]

I usually don't let my diesel idle much either. Even for a few minutes I always use the cruise control which speeds up the idling to 1100 rpm. Also, started using a product made by pittsburgh power called max mileage fuel borne catalyst. One ounce per 25 gallon of fuel. This product will clean up and prevent soot in your engine. If you listen to sirius radio they are on road dog trucking channel (146) on Tuesday mornings from 11am-1pm. I hear lots of postitive things from people who call in to the show. Below is the link if anyone is interested.

https://pittsburghpower.com/products/max-mileage-fuel-borne-catalyst

 

[spoon059]

Yep sure do let it run if I'm only running into the convince store for 30 seconds.. 10 minutes or longer I'll shut it off and command start it

We get about 5 stolen cars a day in my county, mostly from people that leave a running and unattended vehicle. Please turn your truck off and don't increase my car insurance rates...

 

[stimpy433]

We get about 5 stolen cars a day in my county, mostly from people that leave a running and unattended vehicle. Please turn your truck off and don't increase my car insurance rates...

That's DC for you, its full of politicians.... I mean crooks around there!!!