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Old 11-29-2008, 05:25 AM   #1
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I've just got my first DP - 98 Endeavor - and trying to understand the diesel engine. I have the Cummins 5.9ISB. The manual states "Do not idle engine for long periods. Long periods of more than 10 minutes can damage the engine...." My question is: what about when you're stuck in traffic ? And how come many trucks keep their engines running for hours ?

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Old 11-29-2008, 05:25 AM   #2
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I've just got my first DP - 98 Endeavor - and trying to understand the diesel engine. I have the Cummins 5.9ISB. The manual states "Do not idle engine for long periods. Long periods of more than 10 minutes can damage the engine...." My question is: what about when you're stuck in traffic ? And how come many trucks keep their engines running for hours ?

1998 HR Endeavor - Freightliner Chassis
2005 Malibu Maxxi
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Old 11-29-2008, 05:31 AM   #3
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it's referring to idlinign without a load, if your trans is engaged then it is under load; if you need to put it into neutral ther eshoudl be a high-idle setting which is 'safe'; ours goes into high idle if cruise control is on and we press set on the cruise
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Old 11-29-2008, 05:35 AM   #4
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Its a good practise to idle your engine for 5 to 10 minutes when getting off the freeway to let everyething cool down.

Your right trucks idle when sleeping 8 hours at a time.

To be safe I would call the manufacturer ( not the dealer) and ask them to explain their suggestion of not idling more then 10 minutes.
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Old 11-29-2008, 06:34 AM   #5
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Although I'm not a DP owner, out of interest I attended seminars hosted by CAT & Cummins at a couple of FMCA conventions.

What I gleaned from these seminars is that you don't need to idle a diesel engine for extended periods of time.

Those conducting the seminars stated that when you exit after freeway driving, by the time you get to an RV park or other destination the exhaust turbine will have spooled down and cooled down.

They also stated, on start up when leaving a campground or RV park, by the time you do a walk-around checking your coach coach the air pressure should be up to where you can drive off.

Both CAT & Cummins reps commented that all you do by long idles is waste fuel.

When the reps were asked what about truckers who leave their engines idle continually the response was "some do it to keep the cab warm or cool depending on the weather and that the company they drive for is usually paying for the fuel.

I would highly recommend all DP owners, if they ever get the opportunity be sure to to attend these seminars. I'm sure many already have.

The Allison folks also host very interesting and informative seminars at these conventions.

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Old 11-29-2008, 07:58 AM   #6
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I wouldn't be concerned about being stuck in normal traffic, but if your stuck behind a wreck or something that your going to be stopped for an extended period I would either shut down the engine or set it to high idle. 900-1000 rpm.
An idling diesel engine does runs too cool and doesn't completely burn the fuel in the cylinders. This can wash the oil from the cylinders and shorten engine life
Then there's pollution to consider, too.
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Old 11-29-2008, 08:12 AM   #7
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LJA58's advice is right on the money.

Idling in traffic is the same as idling anywhere else. If it is going to be more than 5-10 minutes before you move again, shut it off. If it is stop & go traffic or a traffic light, don't worry about it. It won't be long enough between moving (loading the engine) to be of concern.

Just because truckers do something does not make it a recommended practice. You don't see them idling for long periods much any more either - that was the old days with older engine technologies that fouled easily and started poorly. Now they do it if they need the cab heater, but not much otherwise. And they will run the daylights out of their engine when they stop idling and get moving, whereas RVers typically do not.
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Old 11-29-2008, 09:46 AM   #8
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As a trucker with over 3 million miles I have to agree that there is no reason to idle a MH for extended periods of time. Truckers do it to heat or cool the sleeper while on their 10 hr break. In very cold weather(zero or below) they will also idle to keep fuel from gelling up.
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Old 11-29-2008, 06:35 PM   #9
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We never idle our diesels for over 5 minutes, unless we simply can't avoid it. That includes in traffic.

When departing a campground, we get everything else ready to go except for those things that require the engine to be running, namely building up air pressure. Then we start the engine, retract the HWH jacks. It takes 2 minutes for the HWH system to cycle itself off automatically. By that time the air pressure is up and we're ready to roll. It's much better & faster to warm up the engine under light load than by idling it.

When we arrive at a campground we have invariably driven at least 3-5 minutes at low speeds so we shut down the engine immediately when we pull up in front of the office to check in.

Not only is idling the engine bad for the engine, it wastes a lot of fuel and contributes to pollution.

So why do some truckers still do it? Force of habit it probably the #1 reason. Being a trained diesel mechanic, I've heard all the stories. The two biggies are that (2) it's better for the diesel to let it idle than it is start & stop it, (3) the diesel engine uses almost no fuel at all when idling, and last but not least (4) it's part of the big man image.

(1) Consider this: If the typical truck driver has a 40 year career spanning from the time they're 20 till they're 60, the average truck driver today is 40. That 40-year old truck driver started 20 years ago, and learned most of what he knows--or thinks he knows--from older truck drivers. Guys that were 40-60 years old 20 years ago. Well-meaning, but definitely crusty old guys that would needle a young buck for just thinking about doing things some new fangled way.

(2) If idling was better then the engine manufacturers would say so. But, we have a culture in this country for shade-tree mechanics to think they know better than engineers.

(3) I worked with a bunch of those crusty old guys growing up as a mechanic. They all believed quite strongly that a diesel was so efficient that it hardly needed any fuel at all to idle. Well, the accepted rule of thumb is 1 gallon/hour. The big trucking companies have realized this for a long time, and have had policies to discourage unnecessary idling. As more and more truckers are realizing that idling their engine for an hour while they had lunch just cost them $4-5 for a gallon of fuel, and idling all night long cost them $30-40 they're shutting their rigs down. It adds up even for the RV owner. Thirty minutes in the morning while getting ready to break camp, 15 minutes at each rest stop, an hour during lunch, and 30 minutes when arriving at the CG & setting up. That's 2.5 hours of idling; 2.5 gallons of fuel or better than $10/day.

(4) All you have to do is talk to a few guys with their big DP's about how long they idle their engines and see how defensive they get to understand that a major reason they idle their engines is to look cool. The sound of that big expensive diesel idling is music to his ego.
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Old 11-30-2008, 06:22 AM   #10
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Steve summed up the idling question much better than I could have. He is right on. Doc said he would just let Steve's post go without objecting and then did just that. There is something about a diesel engine idling that makes one want to let it keep purring along, but that has no credible logic after the short cool down period if over. Cummins says 3-5 minutes for the cool down and as Steve writes, you don't need that if you have been driving slowly between the highway and the campground for about five minutes. At a seminar a Cummins rep stated that the life of their engines was based on revolutions. More revolutions idling are revolutions subtracted from their life. Idling compounds the problem by running at less than normal temperatures which can cause fuel washdown of the cylinders. I cringe when I see the large tractors idling for hours.
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Old 12-01-2008, 05:52 PM   #11
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Yep, diesel wash. VERY BAD
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Old 12-04-2008, 04:12 AM   #12
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Diesel idling wastes fuel and adds tons(literally)of pollutants to the atmosphere. This is now recognized by many state governments, who have passed idling laws. Many truck stops now have rows of spaces dedicated to truck cab heaters with an electric outlet included; the cost to the trucker for this is much less than the cost of idling that huge diesel engine for 8-10 hours.
Steve Rankin, thanks for your elequent explanation. May I copy N paste it to other discussions, with a proper attribute statement of course?
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Old 12-04-2008, 05:44 AM   #13
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Actually, when the 24 valve 5.9 Cummins was introduced, there was a problem with bent pushrods (push tubes, in Cummins' parlence) that was traced to engines that had been subject to excessive idling. The problem was that the new 24 valve cylinder head was so efficient in cooling the valve stems that the valve stems and guides ran cold enough during extended idling that varnish would form on the stems and guides causing valve sticking and resultant bent pushrods/push tubes. If the engine was equipped with an exhaust brake, engaging the exhaust brake during idle placed enough load on the engine and raised exhaust temperatures enough to alleviate the problem.

There was a Cummins TSB issued on this topic. HERE is the Dodge TSB that reprogrammed the ECU to deal with the problem. HERE is a Cummins service note discussing the subject.

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Old 12-04-2008, 06:57 AM   #14
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[QUOTE]Originally posted by Ray,IN:

Many truck stops now have rows of spaces dedicated to truck cab heaters with an electric outlet included;

Now if there was only some way to get the states to install these in the roadside rest areas along the interstates, we could all sleep better. Don't you just love the sound of an 18 wheeler idleing while parked next to you in a roadside rest.


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