Diesel Engine Off While Refueling???

[bitNine]

Gasoline has vapors which can be ignited by a spark, and cause a fire. This is why you should always shut down a gasoline engine when refueling, as tons of vapors are released during this process, and sometimes the outside air movement isn't enough to get vapors away from the vehicle. Diesel does not emit vapors like gasoline, and does not explode like gasoline, therefore does not have the same issues as gasoline.

Not sure about the duramax, but the Cummins on my truck has the automatic high idle feature which monitors exhaust temps and other factors of the SCR system. If they are not running optimally, the system will put the engine into automatic high idle. I can also set high idle manually, which I do when I notice it in regen and I'm about to shut the truck down. While you shouldn't let the truck idle for too long, idling when you're working the crap out of the engine shouldn't be a big deal in the long run. You're going to get right back on the freeway and get everything super hot again.

[bitNine]

Originally Posted by SKnight

Got links to back this up? It's news to me.

He's quite correct. It's a well known fact about SCR emissions systems. When exhaust temps aren't high enough, the system can end up creating too much soot through EGR, clogging DPF and making it so that DPF can't get hot enough to burn off the soot, making the entire system work inefficiently. Many of the newer trucks have high idle features which can help with this, especially when intake temps are low.

[avolnek]

Originally Posted by SKnight

Got links to back this up? It's news to me.

Sorry SKnight, I just seen this today.

What exactly are you wanting links to back up specifically?

I will do my best to provide!

[SKnight]

Originally Posted by avolnek

Your newer diesel you are better off not letting it idle too long. Typically if I plan to let mine sit for more than a couple of minutes I will shut it off. Any less and I will let it keep running.
The reason the newer diesels shouldn't idle is due to the new emissions they are installing. Idling is a rather inefficient process with diesels and creates a fair amount of soot and debris from unburnt fuel. The unburnt fuel will begin to plug your DPF filter and either your truck will go into regeneration to clean this filter or worse yet you may need to replace the filter. These filters do have a service life, a fairly long one, but idle time decreases their life.

Thats why they have a front and rear pressure sensor, to motor the condition of the DPF. When the pressure difference meets spec, it goes through a regen process to burn off that soot. The only problem occurs when you don't drive in conditions where a regen can happen, then a forced regen would have to happen but in general that's rare. It's what it's designed to do and pulling a heavy load makes more soot than idling does.

Another down fall to idling for longer periods is that at an idle your fuel pressure isn't very high. Since the fuel pressure isn't very high the spray pattern from your injector isn't at its optimum patter and begins to flush the cylinder walls with diesel fuel. This can get fuel between the piston rings and the cylinder walls and can actually get into the oil.

False. Common rail systems idle at 6,000PSI plus. No worry about fueling issues there, next time you run across someone with a scan tool that has bi-directional control ask them to test the fuel pressure, a Duramax can make 21,000PSI+ at idle. If working properly, those concerns went out years ago, even mechanically injected diesels don't have that issue unless you've got injector problems.

That's why I asked for links, what you said runs counter to an awful lot of GM training I went through.

I'm not advocating never shutting down or leaving it idle during dinner, but you're not going to ruin your DPF or wash down your cylinders either.

[SKnight]

Here's a link to where a guy talked about it, light on needing a regen, highway trip let it regen and self cleared the code.

2013 2500 Longhorn 23 Hrs. of Idle results. - Dodge Cummins Diesel Forum

[silveradoduane]

Originally Posted by bitNine

Gasoline has vapors which can be ignited by a spark, and cause a fire. This is why you should always shut down a gasoline engine when refueling, as tons of vapors are released during this process, and sometimes the outside air movement isn't enough to get vapors away from the vehicle. Diesel does not emit vapors like gasoline, and does not explode like gasoline, therefore does not have the same issues as gasoline.

Not sure about the duramax, but the Cummins on my truck has the automatic high idle feature which monitors exhaust temps and other factors of the SCR system. If they are not running optimally, the system will put the engine into automatic high idle. I can also set high idle manually, which I do when I notice it in regen and I'm about to shut the truck down. While you shouldn't let the truck idle for too long, idling when you're working the crap out of the engine shouldn't be a big deal in the long run. You're going to get right back on the freeway and get everything super hot again.

This does not explain why it is necessary to shut down the engine. Yes gas vapors are highly explosive, but you still have to have an IGNITOR!! Where is the ignitor when the engine is running?? static electricity is the leading cause of gas tank fill fires, but I guarantee you there is not more static electricity in a running car than there is in one that's shut off. The static comes from the human getting in & out of their vehicle. You have failed to disprove my point that leaving your gas engine running during refueling is no more dangerous than fueling while it's off. In my 25+ years of fueling my vehicles, I rarely turn off my engine, & I have never had anything happen. I also make sure I touch the side of my vehicle before I go back to the fuel door to discharge any static electricity. (which has no difference running or not).

[MillerTime]

I never turn of my diesels when fueling, or making quick stops, or durring longer stops in the winter.
50% of the time I turn off the gassers when fueling, but if its cold, I usually leave it on too.
I usually fill up about 3 times a week, no issues so far!

MillerTime- Future Sabre Handler!!

[Crusadernoob]

I don't shut down to fuel, after pulling 19,000lbs for 2-3 hours it's not just EGT's I worry about, the trans. fluid is hot, it won't cool down with the easy run up the ramp and to the pump, if anything it gets hotter as the TCC is no longer locked up and is now slipping and building heat, every thing under the hood is hot, keeping fluids moving is always the best thing if you only stop for 10-15 minutes, less harm in that than shutting it down.

[avolnek]

Originally Posted by SKnight

False. Common rail systems idle at 6,000PSI plus. No worry about fueling issues there, next time you run across someone with a scan tool that has bi-directional control ask them to test the fuel pressure, a Duramax can make 21,000PSI+ at idle. If working properly, those concerns went out years ago, even mechanically injected diesels don't have that issue unless you've got injector problems.



That's why I asked for links, what you said runs counter to an awful lot of GM training I went through.



I'm not advocating never shutting down or leaving it idle during dinner, but you're not going to ruin your DPF or wash down your cylinders either.

I don't need to ask for a scan tool as I am fortunate enough to have many gauges installed on my rig. I can verify you are correct that my common rail actually idles at 7,000 psi.

There is a big difference in 7,000 to 21,000 psi, 300% as a matter of fact. I don't believe the spray pattern would be the same at varying pressures. Simple physics tells you that in a pressure vs orifice spray pattern that pressure changes change the spray pattern.

I cannot verify or prove my beliefs on this matter but I am going off of my own real world experience as far as fuel flow is concerned.

I'd be curious to see a 21,000 psi duramax at idle though if you don't mind, that would be interesting. Also not sure what the benefit of that would be. Ideas?

[Crusadernoob]

21,000psi at idle it will knock like hell!

[MillerTime]

I got my solus ultra in my car, I might go out and read my fuel pressure in my dmax in a few

MillerTime- Future Sabre Handler!!

[SKnight]

A Duramax idling at 21,000PSI actually sounds awesome, like it's got the nastiest racing camshaft you can find.

It's a test, used to establish the integrity of the high pressure side of the system. Any leak at all and it won't achieve it, especially useful when GM required us to figure out which LB7 injector split internally, they'd start spewing at 14,000 or so and would go no higher.

I can assure you, diesel through those micro holes at 6,000+ is a fog. Worked on many that idled all day on job sites, no oil contamination to be found.

[MillerTime]

As promised- desired FRP (PSI) 5176
at idle was around 49xx-52xx
-and screaming at about 2100-2200rpm was at 12,000 ish

EditHighest I can turn the fuel pressure up too on my scanner is a little over 23,000, but im not doing it on my truck. Will on somebody elses if they want me too)
MillerTime- Future Sabre Handler!!

[bitNine]

Originally Posted by silveradoduane

This does not explain why it is necessary to shut down the engine. Yes gas vapors are highly explosive, but you still have to have an IGNITOR!! Where is the ignitor when the engine is running?? static electricity is the leading cause of gas tank fill fires, but I guarantee you there is not more static electricity in a running car than there is in one that's shut off. The static comes from the human getting in & out of their vehicle. You have failed to disprove my point that leaving your gas engine running during refueling is no more dangerous than fueling while it's off. In my 25+ years of fueling my vehicles, I rarely turn off my engine, & I have never had anything happen. I also make sure I touch the side of my vehicle before I go back to the fuel door to discharge any static electricity. (which has no difference running or not).

A spark is not the the only thing that can trigger a gasoline vapor fire. The autoignition point of gasoline vapor is 495 degrees Fahrenheit. This means that when vapors come into contact with ANYTHING that is at or above that temperature, the vapors WILL ignite. An example of something that is greater than 495 degrees would be exhaust gases. Why must we shut off our vehicles? Not because YOUR exhaust gases might ignite gas vapors (tail pipes, when not straight out the back, typically exit on the side of the vehicle opposite the tank fill), but because your pump neighbor's continual exhaust gases could. While quite unlikely, shutting down your engine reduces exhaust gases near gas vapors. It's not about prevention, it's about keeping chances low. Anything can happen at any time. Cell phones have been found to be extremely unlikely to ever be able to cause the conditions which would ignite vapors, yet gas stations still ask us not to use them. This is the CYA factor. One fire can kill everyone at the station. While I, like you, have spent even more time filling gasoline tanks, vehicles, and numerous other items, and never had a problem, there's a very good reason why small engines always say to wait for the engine to cool before filling the tank. Gasoline vapors can ignite from the heat of a muffler or catalytic converter. It doesn't require a spark.

[silveradoduane]

Originally Posted by bitNine

A spark is not the the only thing that can trigger a gasoline vapor fire. The autoignition point of gasoline vapor is 495 degrees Fahrenheit. This means that when vapors come into contact with ANYTHING that is at or above that temperature, the vapors WILL ignite. An example of something that is greater than 495 degrees would be exhaust gases. Why must we shut off our vehicles? Not because YOUR exhaust gases might ignite gas vapors (tail pipes, when not straight out the back, typically exit on the side of the vehicle opposite the tank fill), but because your pump neighbor's continual exhaust gases could. While quite unlikely, shutting down your engine reduces exhaust gases near gas vapors. It's not about prevention, it's about keeping chances low. Anything can happen at any time. Cell phones have been found to be extremely unlikely to ever be able to cause the conditions which would ignite vapors, yet gas stations still ask us not to use them. This is the CYA factor. One fire can kill everyone at the station. While I, like you, have spent even more time filling gasoline tanks, vehicles, and numerous other items, and never had a problem, there's a very good reason why small engines always say to wait for the engine to cool before filling the tank. Gasoline vapors can ignite from the heat of a muffler or catalytic converter. It doesn't require a spark.

I guarantee you that with a temperature of -30 & a wind chill of -50, nothing outside in South Dakota is anywhere close to 495 degrees. Even in the summer time, I don't think it would be possible to ignite vapors with exhaust that has traveled 5 or 10 feet. Another factor here in SD is 90% of the days of the year the wind is blowing 20mph or more. We have had a constant wind of 30-40mph for the past week straight with an air temp in the 40's. I don't think ignition would be possible. & as far as exhaust system goes, It would not cool down at all in the amount of time it takes to fill with gas. Another factor is that here in SD I am quite often the only person at the gas station. I guess we just don't have the same conditions as everywhere else. I still hold to my stand that I don't think it's any riskier to leave your engine running than it is to shut it off.

[avolnek]

Originally Posted by SKnight

A Duramax idling at 21,000PSI actually sounds awesome, like it's got the nastiest racing camshaft you can find.

It's a test, used to establish the integrity of the high pressure side of the system. Any leak at all and it won't achieve it, especially useful when GM required us to figure out which LB7 injector split internally, they'd start spewing at 14,000 or so and would go no higher.

That's actually a really interesting way to perform the leak down test! Can't say I'd want it done on mine, but can't see how it would really damage anything either, just more paranoid I guess...

I will have to look more into the idea of cylinder wash down during idle. From some of the looking I have done since you questioned this it is a highly debatable scenario with no real facts defending either side. Many have said they feel it washes the oil from the cylinder wall each time the piston goes through it's motion, but haven't see any proof of such...

[Bryce]

Effects of Gasoline Vapor Towards Diesel Engine - YouTube

this video is interesting.

I guess is some jackass dumped a bunch of gasoline near a running diesel, there is a slight chance of a run away.

[OL Creeker]

I never shut down for fuel

[bitNine]

Originally Posted by silveradoduane

I guarantee you that with a temperature of -30 & a wind chill of -50, nothing outside in South Dakota is anywhere close to 495 degrees. Even in the summer time, I don't think it would be possible to ignite vapors with exhaust that has traveled 5 or 10 feet. Another factor here in SD is 90% of the days of the year the wind is blowing 20mph or more. We have had a constant wind of 30-40mph for the past week straight with an air temp in the 40's. I don't think ignition would be possible. & as far as exhaust system goes, It would not cool down at all in the amount of time it takes to fill with gas. Another factor is that here in SD I am quite often the only person at the gas station. I guess we just don't have the same conditions as everywhere else. I still hold to my stand that I don't think it's any riskier to leave your engine running than it is to shut it off.

You can talk about the lack of likelihood, and you're right that it's not going to happen everywhere. But it CAN happen, has happened, and will continue to happen, whether or not it's happened to you or me. The rule is there for reduced risk, because it's a well known fact that gasoline vapors can, and do, ignite in the right situations, without a spark. If you believe that a running (or hot) engine doesn't increase risk in any way, then more power to you, but it's just not true. History of the entire world filling vehicles with gasoline, gives us that information. Even if it only slightly increases the risk, there is an increased risk. It wouldn't be prudent to base your opinion of whether or not there's an increased risk, solely off of your own experiences. Your experiences are less than 0.000000001% of the available data.

I'm only pointing out what the available data says, even though that I know, just as well as you, that the risk of it actually happening on a cold, windy, winter day, is slim to none. It's undoubtedly more likely on a hot, calm, summer day, when vapors are allowed to saturate an area.

[SKnight]

Originally Posted by avolnek

That's actually a really interesting way to perform the leak down test! Can't say I'd want it done on mine, but can't see how it would really damage anything either, just more paranoid I guess...

I will have to look more into the idea of cylinder wash down during idle. From some of the looking I have done since you questioned this it is a highly debatable scenario with no real facts defending either side. Many have said they feel it washes the oil from the cylinder wall each time the piston goes through it's motion, but haven't see any proof of such...

The pressure test is actually part of the diag procedure for a P1093 code, on the 2001-2004.5 Duramax trucks the injectors were famous for rupturing internally and losing fuel into the oil. The code is defined as low rail pressure during fuel enrichment, so you would connect the scanner, command the pressure to max and see how much the system would make. The LB7 engines topped out at 21,000PSI but with a bad injector would usually stop at 14,000 or so, anything + - 1,000PSI I believe, and it failed the test. Write it up, order a set of injectors and gaskets per the bulletin.

Interesting side note, a Duramax engine can hold 32 quarts of liquid in its crankcase before it comes out the breather hole in the side of the block. When they came with that code my first move was to check the oil, find it a foot up the stick, then check the fuel pressure. They filled the pans full of diesel. My 8 gallon drain pan would get filled completely up with what was actually pure diesel as all the oil was long gone out the separator. Believe it or not, never had a single bearing issue, engine or turbo, and some of those engines I worked on for over 200,000 miles.

I feel that the cylinder washing rumor stems from the old mechanical injected gasoline engine days. If the idle speed got low, or the injectors got weak, the injectors would dribble and non atomized gas doesn't burn well at all, even if the cylinder fired. Raw gas got by, rinsing the oil off the walls, making the rings lose their seal, allowing more blowby, losing power in the cylinders, lowering the idle, making it worse. Lots of folks have likened the very similar appearing diesel injection systems to those days, but the diesel injector cracking pressure is so high on the mechanical injectors, and through the roof on the electronically fired ones, that it would skip due to the fuel being improperly atomized.