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Discussion Starter · #1 ·
Ok this guy I work with has A dodge with all the gee wiz computer stuff on it to make a bunch of power.

we were comparing notes and came across a disagrement in our understanding. This guy seems reliable but i had never heard his ideas.

The Question was: Is Idling bad? He said he never Idles his cummins, he said there is a danger of washing the cylinders with Fuel and scoring them.

I on the other hand will leave my truck running for hours while i go to the store etc. My thinking is that startup is the hardest on multiple componenets and Idleing has the least amount of fuel per cycle so i cant imagine washing the rings clean of oil.


Any thoughts?
 

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I've always heard the diesels handle idling much better than gas engines. Recently, I've heard that it's a bad idea, but I think that's mainly driven by the eco-nazis, unless maybe it's due in part to the newer designs.

I think idling while your spending a lot of time in a store is unnecessary and just burning up fuel. Semi drivers idle to keep warm and electrical provide power while not-driving, so they're still using the engine for business (using the engine as a tool).

Disclaimer........ I have no practical experience in this area.
 

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Discussion Starter · #3 ·
I leave it running cause im from texas and its semi arctic here in Kentucky by my standards. BUt I have heard the new Diesel with the Particulate filters dont like idleing, but i always heard low fuel consumption at idle was the diesels bread and butter.
 

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one of are fire trucks a GMC topkick with a cat can't think which one at idle it loads up and starts to spit and spuder, and if you idle it up to about 1100 RPM's it runs alot beter. just my .02
 

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i was gona say majority of our fire trucks sit idling most of the time, dont think we have ever had engine trouble due to this. we keep out trucks for 20 years.
 

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Discussion Starter · #6 ·
I guess there IS a debate about it!!
 

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w have 4 or 5 diesel fire trucks and the GMC is the only one that loads up like that, maby its just the cat are cummins, powerstroke, detroit, duramax don't do it.
 

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w have 4 or 5 diesel fire trucks and the GMC is the only one that loads up like that, maby its just the cat are cummins, powerstroke, detroit, duramax don't do it.
If the GMC is a Detroit 2-stroke, I believe Grigg (or somebody) mentioned that it wasn't good to idle them. Seems like it was something to do with them running too cool and thermal contraction causing problems. I don't recall anything with certainty, However.
 

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The only issue from idleing for long periods of time would low oil pressure. Us semi truck drivers just kick up the idle a little bit to get the oil pressure up.
 

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It's not good to idle any engine, but repeated starts aren't good either.
Bit of a balancing act really.
 

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The cummins service manual for the b series says not to idle for more than 5 minutes.
 

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Discussion Starter · #13 ·
Thats pretty much from the Horse's Mouth. Huh, I always thought Idling was like being turned off to a diesel. I stand very corrected.

The cummins service manual for the b series says not to idle for more than 5 minutes.
 

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i been letting it idle for 10 minutes now since its getting below freezing, i know it vibrates the mofo out of my truck. guess ill have to put a brick on the peddle and up the rpms 2-300
 

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Guys,

Idling is generally bad for ALL motors including diesels. I'll explain why. When the EGT's drop generally below 300*F you start getting incomplete combustion of the diesel fuel...... this diesel fuel then starts running down the cylinder walls and 'washing out the cylinder' aka fuel deteriorating oil films for protection. (Think paint thinner being thrown on a freshly painted wall.....) NOW That being said there are a TON of ways to combat this. An exhaust brake will generally keep EGT's well above 500*F which will allow for a complete burn of fuel and prevent cylinder wash from occuring......

Also... the Dodge Rams for example (2003+ I think) have a 'High Idle Feature' that can be enabled at a dodge dealership that will allow a truck to be placed in park, the driver will then turn ON cruise control and the motor will spike to 1100 RPM's.....the user can then use the accel + or decel - buttons to move the idle manually up or down 100 rpms at at time from 800 or up to 1300 RPM's.. this high-idle feature will also generally keep EGT's up to 400+*F and allow for a complete burn.......

mufflers etc can also had a back pressure and allow EGT's to increase.....

aka if your a straight pipe common rail...... yea idling is indeed bad for your motor if your not enabling an exhaust brake or high idle feature..... I don't care who you are, if you been doing it for 10+ years etc etc etc.... its bad for your motor if your not taking a proactive approach.

I dunno about anything regadring chevy or ford's way to combat this.... or if they even can.......

Big Rigs have an EGT monitor system that will periodically either load the motor (air compressor load, or high rpm, or exhaust brake etc etc etc) to keep EGT's in check.... (these are monitored) Otherwise I've heard the ford automatic guys simply putting their trucks transmission in drive and putting the E brake on to load the motor to keep EGT's high...

All I got...... its simple science.... so if you say its 'okay for your motor' your simply just incorrect... science trumps....

MOST.. (ALL) recent diesel motors have a high idle feature utilized in cold start ups that allow this to be generally okay.

~M

EDIT: In reagard to pre-1990 technology.... I have no idea how they were idling overnight etc or if the motors have enough parasitic drag in them back then to keep EGT's above the magic 250-300*F mark...... I simply don't know......
(I want to say it is probably due to "indirect injection" which has a small 2ndary combustion chamber... this small delayed burn brings EGT's simply higher at idle then a direct injection (modern) motor.....

Older motors couldn't get the high PSI out of the pumps to do direct injection (I THINK)



That being said... the dodge I'm looking at buying will have a neutral safety switch 2ndary pin relay put in at the dealer to allow the manual transmission truck to also use the cruise control high idle feature with the transmission in neatural and the e-brake despressed.......

Tap the brake and the idle returns to 700ish.......along with EGT's to that magic 200-250*F where cylinder wash process begins.....
 

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not only can excess fuel wash out cylinder walls,the cool vapors get sent out the exaust,which mixes with the soot that all diesel,especially "old school" types that we love,produce.
this sludgy,oily mix will solidify in the exaust ports,closing them off.the sludge,having loads of carbon (soot) mixed in,will grind slowly away at the exaust valve stems and seats.

not only should they be run at high idle,diesels should be run under enough load to heat exaust gas to the point that the sludge burns off.
we had a few gen sets at work that were run under high idle at low or non existant load...they would coke up to the point that the exaust would dribble sludge.when they got loaded up,and ran hot,they would always run like crap for the first hours or so,and blow chunks of oily soot all over everything.

run properly ,these engines (perkins) would normally run well for over 12000 hours before they gave trouble....the coked engines never ran well.often getting to the point that they could not carry thier rated load.they died an early 5000 hour death.(valves shot,blowby etc).

idling's not good...but hard to avoid in our part of the world.when it hits -40 *c,it's usually a lot more trouble to shut the engines off.we sometimes rig up load cells to make the gen's work hard enough to stay warm.
 

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Note of semi personal experience on pre 1990 commercial diesels and extended idling.

My father used to have a 1975 Kenworth (owner operator) that he'd had repowered with a 400 "big cam" Cummins (13 speed Road Ranger, doesn't matter for this though ;) ).

We're in Alaska, he used to haul to Prudhoe bay, even in the winter.

Durring white out conditions he would let it idle, until the weather cleared, as the engine was unlikely to restart if shut down at those temps (5 decades + below 0 F).

He added throttle advance, not because of condensation, or concretion of the soot; it would freeze his ass at low idle during those times (low idle, arctic conditions).

FWIW I got to ride along to Prudhoe bay circa 1982, in the summer though. ;)
 

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Ok this guy I work with has A dodge with all the gee wiz computer stuff on it to make a bunch of power.

we were comparing notes and came across a disagrement in our understanding. This guy seems reliable but i had never heard his ideas.

The Question was: Is Idling bad? He said he never Idles his cummins, he said there is a danger of washing the cylinders with Fuel and scoring them.

I on the other hand will leave my truck running for hours while i go to the store etc. My thinking is that startup is the hardest on multiple componenets and Idleing has the least amount of fuel per cycle so i cant imagine washing the rings clean of oil.


Any thoughts?
I have a white paper from Cummins showing fuel consumption per RPM and idle is almost double that of 1650 RPM which is the least consumed.
this is on a 4BT so...
 

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I have a white paper from Cummins showing fuel consumption per RPM and idle is almost double that of 1650 RPM which is the least consumed.
this is on a 4BT so...
Ummmm.... shouldn't be entirely true.... the overall 'consumption rate per RPM' aka effiecency will be higher at 1650 which is when the cummins makes its best thermodynamic utilization of fuel/combustion/empathy utilization......

But for actual "FUEL CONSUMED" The lower the RPM the better...

At 650-800 RPM the Cummins (or all diesel engines for that matter) are simply having combustion temperatures too low in order to complete burn off and utlilze every bit of fuel being injected......

At 1650 though per say..... its a combustion party and every last drop is invited.......

PAGE 28 in the CUMMINS FUEL ECONOMIC IMPACT will show the fuel consumption rate in liters per hour of idle at 1100 vs. 650... and its on the magnitutde of 1.9L an hour at 650 to 3.8L an hour at 1100 for low and high idle applications.

By increasing your idle.. I want to make it clear to everyone though.....you will not 'save fuel'........ (which CCpanel I don't think was trying to convey.... just the overall efficiency drop)

^^^^ I just wanted to clarify that last statement before we had a noob or a wish modder come in here and adjust their idle up to 1650 and say hey I'm saving the enviroment and burning up a clutch for fuel savings!

Heres the link directly from cummins....

http://www.gogreenfleetsolutions.com/tools/Cummins_Fuel_Economy_Guide.pdf
 

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All new over the road trucks have a feature that shuts them down after 5 minutes of idling, mandated by the EPA. My 2001 Dodge has a feature for colder weather that will idle the truck up to 1100 rpm and if it's really cold it will only send fuel to 3 cylinders. It sounds like a total box of rocks when it does this especially on a cold start but it makes the EGT's scream up and warms the engine nicely.
 
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