Extended idling on Dodge vs. Big Rigs

[HeavyHauler]

With all the talk about not letting your truck idle for more than 5 to 10 minutes because of the chance of unburned fuel "clogging" your engine, I wondered what made it different in a big rig for them to be able to idle all day and all night and still run over a million miles?



Why don't they have problems with unburned fuel as everyone says we do?



Hope some educated source can shed some light on this matter; I'm sure there's plenty of people out there that want to know the answer to this question.



Thanks.

 

[LightmanE300]

Big rigs have a 'high idle' setting designed for extended idling. The rpm setting our trucks have is low as is the amount of fuel used, and there is risk of excessive blowby, carbon formation, etc, etc. There really is no need to idle our trucks any longer than 5 mins... just turn it off and start it back up again... it won't hurt anything...

 

[Turbo Tim 1]

Most big trucks built now will shut off after a few minutes unless the idle is ramped up like to run a pump or blower. It is more of an EPA thing than anything. There are people here that have idled their trucks for a long time with no known side effects. The key is keeping engine temperatures up either by running higher idle speeds or closing an exhaust brake. There is a TSB for bent push rods on 24 valve engines due to extended cold idling and Dodge and Cummins now programs them to idle up to 1200 rpm in the event that coolant temperature drops below 140 degrees and ambient is below 32 degrees I believe. If I am running in to the store for 2 minutes I leave it running, if I am going to be more than 5 I'll shut it down. Alot of rest areas have signs that say you can't leave your truck running now. my 2 cents

 

[HeavyHauler]

Originally posted by Turbo Tim 1

There is a TSB for bent push rods on 24 valve engines due to extended cold idling and Dodge and Cummins now programs them to idle up to 1200 rpm in the event that coolant temperature drops below 140 degrees and ambient is below 32 degrees I believe.

Is this on the 2nd generation trucks or the 3rd generations? If this is the case, we could leave our trucks idling all night and not have to worry about anything.

 

[illflem]

The biggest danger in extended idling is what's called cylinder washdown. Cool cylinder temps create unburnt fuel that washes the lubricating oil off the cylinder walls. I don't have to explain why that is bad. The unburnt fuel ends up in the engine oil, diluting it. I can always tell an engine that has been over idled by sniffing the dipstick, it will smell like diesel.

The main problem with washdown occurs when the engine is stone cold and the idle extended to try and warm it up, once an engine has reached operating temperature I wouldn't worry as much about extended idling.

Don't see how washdown wouldn't apply to all generations.

 

[LightmanE300]

Illflem is correct, saying exactly what I was saying with my loosely used term 'blowby'... . I meant the same thing... . washdown. Turbo Tim says many have idled them for long times with no problems... . have they done oil analysis to check for fuel dilution or are they judging 'no problems' by the fact their truck didnt' die and drove off the next morning? Best thing you can do is listen to your owners manual and cummins and shut it off.

 

[Turbo Tim 1]

Lightman, I was just stating as to what other people have said, that they let their trucks idle for extended periods and have XXX,000 miles on it. I don't know if they have done oil analysis and frankly I don't care. As you can see by my post I don't idle my truck for extended periods. Heavy hauler, the TSB was for 2nd gen trucks.

 

[Hale on wheels]

Is this only a problem when the ambient temperature is low? For instance, here in Texas, could I idle my truck for long periods of time during the summer or when the temps are high?

 

[berg]

Originally posted by LightmanE300

Big rigs have a 'high idle' setting designed for extended idling. The rpm setting our trucks have is low as is the amount of fuel used, and there is risk of excessive blowby, carbon formation, etc, etc. There really is no need to idle our trucks any longer than 5 mins... just turn it off and start it back up again... it won't hurt anything...

Its ok to turn em off but we work out side all day and the only heat we have is our truck heater and they really don't work to good with the engine off

 

[RustyJC]

Originally posted by Hale on wheels

Is this only a problem when the ambient temperature is low? For instance, here in Texas, could I idle my truck for long periods of time during the summer or when the temps are high?

Ambient temperature has very little to do with it. Exhaust temps idling with the exhaust brake off run around 200 to 250 degF on my truck. Turning the e-brake on increases the EGT (pre-turbo) to maybe 400 to 450 degF. Even that's a little low to completely prevent varnish buildup on the valve stems (which ultimately leads to valve sticking and bent pushrods), but it's better than 200 degF without the brake!



Rusty

 

[HeavyHauler]

Another question...

How can owner-operators afford to run their trucks all night at the Flying J while they sleep?



I've heard that big rigs burn virtually no fuel at idle, but if this is true, how do they do it? What makes them not burn any fuel at idle when the ISB 5. 9 obviously does?



Thanks for all the replies.

 

[C. Harlan]

because when they get fuel from the flying J, they are actually burning off the water and mud in the fuels! the flying jack@ss, as I call it, here in San Antonio, has been shut down for contaminated fuel containing mud and water numerous times. Just thought I would chime in. I idle my truck frequently, as when I am pulling, get out for say, 20 mins, get back in, and motor back on... I do this frequently... yesterday, I was at Discount tire, getting more new rubber, and put my throttle stick under the dash, and revved it up to about 1100-1200 rpm, and took a nap while waiting... EGT's were ~150°-200° post turbo... that is not too bad, is it??



-Chris-

 

[David Oxland]

I think the question you need to ask yourself is; Why would you want to do this extended idling?

Some of the reasons were, in years gone by,



-Starting a cold engine was prone to slow oilup which is not really a factor any more on account of modern multi-vis oils and well designed oil systems.



-In the old days big blocks were more prone to cracking due to uneven heating during warm up and poor manufacturing process



-It gave you a gooshy feeling to warm the thing up very... ... ... ... ..... slowly, it was considered being kind to the engine.



Cold diesels with their starting starting systems were sometimes difficult to get going.



On the other hand



-Modern manufacturers do not advocate long idling periods for the following reason; poor atomization at low speed and low temps. This means that the fuel doesn't start burning promptly and does not burn completely.

Some of it, the raw part, runs down the cyl walls as Bill said and some sticks to the cyl head while some, partially burned, gums up valves in the stem and seat area and some ends up on the turbine blades and all down the exhaust. Exhausts occasionally catch on fire on account of this.

-For those who are in cold country and think that keeping the engine running so that the incoming air will be warm; Have a look at the whole induction system and while it's idling in cold conditions go and feel the intake manifold and you'll see how cold the intake air really is. I don't think that winter fronts will help to keep up the charge air temperature very much. A diesel needs Hot air for prompt comencement of combustion.



I think that after all said and done "Long idling is an old practice from old timers" I'm one of them and over the years working with newer machinery have learned the truth of where we are now.



Notable also is the availabity of very small generator to provide cabin heat and air conditioning while using it's cooling water to keep a big over the road engine warm as the driver sleeps. The reason is to get away from the long idling periods.



By the way, if you don't except the washdown statements do some oil samling under these abusive conditions and watch the fuel dilution start to rise.



Notably I think the the common rail setup may have some advantages in premoting good combustion at low rpm and cold running conditions



David

 

[illflem]

A lot of the big rig fleet operators (at least the ones who are making money) are now installing timers to prevent extended idling and are using Webastos heaters similar to the Espar. Some use electric heat for sleeping, lot of truck stops now have plug-ins. The big operators know where their bottom line is with fuel consumption and engine longevity and don't overnight idle any more.

Sometimes a refer unit with separate engine is mistaken for an idling truck.

 

[truckstom]

David Oxland is right on the money... I agree. I remember being told long ago "let it warm up for at least 30 min. " Hell, I still do that.

As far as big rigs not using fuel while ideling... I've got the Cat ID, in my Freightliner, which is a computer screen on the dash. I can scroll thru it and find just about anything I want about my engine... rpm's, water temp, boost, fuel temp,... the list goes on. I use 1 gallon of fuel per hour idleing with the a/c on. I've been idleing for a long time prolly always will to some degree. but it's not needed today as it once was, or believed it was.

 

[klenger]

I think that one of the reasons that the big rigs claim that ideling does not use any fuel is because they are buying a couple hundred gallons of #2 at a time. It's just a drop in the bucket, as they say.

 

[Hohn]

There's no reason to idle our trucks for the benefit of the engine. If you do idle it, it's for YOUR convenience...



Simple fact is, diesel engines are designed to be under load or not operating at all. EGT get's a lot of attention on here for being too high, but no one seems to talk about the dangers of being too low.



The EGTs are simply to low when operating at idle for prolonged periods. Others have listed above the reasons this is bad.



I don't plug my truck in at night. When I fire it up in the morning, it's pretty cold. BUT, I know that the engine simply doesn't generate much heat at all sitting there idling. Those people who start the truck and let it idle to "warm up" are doing their engine a disservice. So the BEST way (imho) is to simply fire it up and go when you see oil pressure. I keep it under 2K rpm for the first few minutes, then drive it like normal. When I get on the interstate, I dig deep into that pedal, right onto the verge of smoke. That way, I can get some heat into the engine, and everything is happy-- EGTs come up, turbo gets some heat, and the coolant gets some heat (as do I sitting behind the wheel).



Starting a cold truck and letting it idle to "warm up" is a waste of time, IMHO.



Hohn

 

[skobylenski]

I only start and idle the truck until all 6 cylinders are firing (in the winter, that is). When it's warm, I just get in and go. As for leaving it running when I stop - if I'm just running in to the post office, bank, or general store to do a quick errand, I'll leave it running, especially in the winter. Other than that, I'll shut it down.



Just my $. 02

Scott

 

[HeavyHauler]

I don't believe that I was asking about the benefits or disadvantages of idling.



I was asking why big rigs will idle all night and can still get the kind of mileage that they do out of their engines as opposed to our engines. Everyone adamently states on this forum that extended idling is detrimental to engine life but it obviously isn't on big rigs. I wanted to know what was different about them from Dodges.



I would appreciate everyone sticking to the topic and not talking about something that you know about. If you don't know the answer, don't respond.

 

[Hohn]

Very well, then HH:



Big rigs have electronically controlled idlers many times. These controllers automatically start, stop, and idle the engine to maintain a certain temperature range.



If you mean mileage in terms of MTTO or MTBF, then this explains why they last so long-- they are temperature-managed.



If you mean mileage, as in FUEL mileage, well it a matter of proportions. As someone stated, the amount of fuel burned by an idling class 8 rig, is MUCH less than when it is charging up a hill with 80K behind it.



Our CTDs also don't use much fuel at idle, but PROPORTIONALLY, the CTD might use more fuel at idle than a big rig might.



IF a class 8 only burns 1 gph at idle, then that's just a drop in the tank. .



I wonder how much a CTD burns in gph when idling...



HOHN