Base Idle, Fast Idle, Non Idle - Best Practices Diesel

NeverHome2 wrote:
In October 2004 I took delivery of a new Peterbilt 379 127" BOC, 248" wheelbase, 70" sleeper, all the options available. The first Cat C-15 with Acert emissions and two turbos delivered in our area. I read all the manuals on the new engine. Had an 18 speed transmission and the max HP then, 550. This was by the way my 4th computer engined truck and I read all those manuals too.

Cat recommended no warmup, no idle down unless working very hard. The three minute idle rule was legislated by states and towns to stop noise. Has not a thing to do with the engine. Once oil pressure is up go to 1000-1200 rpm for warm up if ambient temps are under 32 degrees F.

We truckers would high idle our trucks when stopped for heat or A/C. Its rough sleeping in the truck when its not comfortable. If you stop for fuel its not efficient to shut the truck off when your going to leave immediately after. In the winter frequently the truck would run for the whole trip, sometimes up to 6 weeks. You will never go to that extreme in your motorhome so why all the discussion? If I was rich I could have purchased and installed an auxiliary engine and generator but they cost so much and add weight which lowers your pay. Your motorhome has one so you can shut the big engine off and keep warm or cool and charge the batteries.

So I find this discussion a pure matter of common sense and personal preference.

I think you may be correct. Since we barely use our engines, I wonder how much harm we could possibly do even if we idled for 10 minutes before we left and never high idled at all. I'm guessing it wouldn't be very good for the engine, but since we use our engines such a tiny amount compared to what they are designed for, does it really matter? I get the impression that best practice is to idle the least amount of time possible, but, as you've said, it's probably a matter of personal preference for our application.

In October 2004 I took delivery of a new Peterbilt 379 127" BOC, 248" wheelbase, 70" sleeper, all the options available. The first Cat C-15 with Acert emissions and two turbos delivered in our area. I read all the manuals on the new engine. Had an 18 speed transmission and the max HP then, 550. This was by the way my 4th computer engined truck and I read all those manuals too.

Cat recommended no warmup, no idle down unless working very hard. The three minute idle rule was legislated by states and towns to stop noise. Has not a thing to do with the engine. Once oil pressure is up go to 1000-1200 rpm for warm up if ambient temps are under 32 degrees F.

We truckers would high idle our trucks when stopped for heat or A/C. Its rough sleeping in the truck when its not comfortable. If you stop for fuel its not efficient to shut the truck off when your going to leave immediately after. In the winter frequently the truck would run for the whole trip, sometimes up to 6 weeks. You will never go to that extreme in your motorhome so why all the discussion? If I was rich I could have purchased and installed an auxiliary engine and generator but they cost so much and add weight which lowers your pay. Your motorhome has one so you can shut the big engine off and keep warm or cool and charge the batteries.

So I find this discussion a pure matter of common sense and personal preference.

holstein13 wrote:

FIRE UP wrote:
Well,
Never seen so much talk about idling a diesel. After over 35 years of running, driving and maintenancing diesels on FD, we two reasons to mess with the idle.

At the Spartan factory a few weeks ago, they couldn't stop telling us how hard the fire departments are on their vehicles, for a number of reasons. Yes, they race from place to place in stop and go traffic and are weighted with heavy water and gear, but also, Spartan claims that there is a different breed of person who can do the demanding and dangerous job of firefighting and they aren't always apt to care for the equipment properly. They are more "Get 'er done" type people.

holstein13,
Without deviating too far from the original subject line here, yes, we were hard on equipment. It's the nature of the game. It came with the territory, and all the other clichés. And, just like Cops, Air plane pilots, Computer engineers, and any other walk of life, there were/are good firemen and, BAD firemen. I was waaaaaaaay more into maintenance/preservation/alteration/fabrication etc. than about 95% of the rest of the personnel on our department.

Some of the guys could care less, all they wanted was paycheck and would barely do what was required of them. Others, were really into it and, put a lot more than what was required. I did it all. I outfitted them, worked off of them, welded on them, altered them, taught about them, and much more. It was fun, then I retired and, THAT'S A LOT MORE FUN!

We used those trucks to the maximum. But, we also kept them up as, if we didn't, when someone called 911, there would be no trucks to respond. Our criteria then, (and I'm assuming still, been retired for 6 years) was that the front line fire engines/trucks, had to last for 15 years. Then, they had another 5 years as a reserve unit. And while most met that criteria, some bit the dust way ahead of time.
Scott

holstein13 wrote:

Tom/Barb wrote:
I believe much of the high idle thinking is left over from the olden days of diesel. these new computer controlled engine are smarter than many who operate them.

I see no valid reason to fix some thing which isn't broke.

Or should I fix it until it is?

What exactly, do you think is being controlled by the computer? Certainly not the switch from base idle to high idle. The computer does nothing to help us.

The manual says to not idle for long periods of time, but doesn't offer any guidance on what that means. The computer doesn't care and doesn't control this. It will let us slow idle until we run out of fuel.

What exactly do you think we are trying to fix?

my whole ECM is computer controlled. I have no direct linkage to the engine, With Caps system every thing the engine does is computer controlled.

FIRE UP wrote:
Well,
Never seen so much talk about idling a diesel. After over 35 years of running, driving and maintenancing diesels on FD, we two reasons to mess with the idle.

At the Spartan factory a few weeks ago, they couldn't stop telling us how hard the fire departments are on their vehicles, for a number of reasons. Yes, they race from place to place in stop and go traffic and are weighted with heavy water and gear, but also, Spartan claims that there is a different breed of person who can do the demanding and dangerous job of firefighting and they aren't always apt to care for the equipment properly. They are more "Get 'er done" type people.

FIRE UP wrote:
Well,
Never seen so much talk about idling a diesel. After over 35 years of running, driving and maintenancing diesels on FD, we two reasons to mess with the idle.

1. Increase for
A. Maximum electrical load, i.e. All emergency lights
B. A/C on and operating
C. Search lights on and operating

2.Increase for
A. Engine temp operational limit reached

As for our '04 Itasca Horizon, 36GD with the C-7 330HP CAT, I increase the idle for air build up and, after hitting the Store button on the HWH leveling control panel.

Other than that, no real reason for increasing it. I'm sure as heck not going to worry about it at a stop light.
Scott

Well, your 35 years of knowledge is probably OK but you can forget most of it. Ever since the government and epa got involved and started to choke diesel engines with low lead fuel and emission controls it's a NEW ballgame. You might ought to read up on the NEW diesel engines with all the epa **** on them. lol

Well,
Never seen so much talk about idling a diesel. After over 35 years of running, driving and maintenancing diesels on FD, we two reasons to mess with the idle.

1. Increase for
A. Maximum electrical load, i.e. All emergency lights
B. A/C on and operating
C. Search lights on and operating

2.Increase for
A. Engine temp operational limit reached

As for our '04 Itasca Horizon, 36GD with the C-7 330HP CAT, I increase the idle for air build up and, after hitting the Store button on the HWH leveling control panel.

Other than that, no real reason for increasing it. I'm sure as heck not going to worry about it at a stop light.
Scott

Mr.Mark wrote:

DSDP Don wrote:
"holstein13"......The reason "Mr.Mark" stated that he waits a minute before engaging high idle, is to allow the oil to get circulated through the engine. You don't want to go from a cold start to half throttle.

On older coaches, probably 2007-2008 and older, you could adjust the base idle from the Smart Wheel. You could adjust it up or down in 25rpm increments with the cruise. I mention this, because it's easy to lower the idle accidentally without realizing.

I will be at the coach on Monday (it's in service in FL) and will look at the manual. I read in the manual that there is a delay just as DSDP DON explained.

Thanks, I'm definitely interested in the answer and I'll try to look it up for my coach as well. I wonder if there is a delay how long should we wait and will the computer allow us to raise it to the point that it could harm the engine.

DSDP Don wrote:
"holstein13"......The reason "Mr.Mark" stated that he waits a minute before engaging high idle, is to allow the oil to get circulated through the engine. You don't want to go from a cold start to half throttle.

On older coaches, probably 2007-2008 and older, you could adjust the base idle from the Smart Wheel. You could adjust it up or down in 25rpm increments with the cruise. I mention this, because it's easy to lower the idle accidentally without realizing.

I will be at the coach on Monday (it's in service in FL) and will look at the manual. I read in the manual that there is a delay just as DSDP DON explained.

MM.

Koop wrote:
Per my owner's manual, I always start my engine at low idle speed ~500rpm. After oil pressure is established - a few seconds at most - I use the idle speed control rocker switch to raise the idle in 25rpm increments to ~700rpm. Then I use the smart wheel cruise control to hit 1,000 rpm to build air pressure and warm the engine as quickly as possible. My Allison manual recommends 700 rpm input shaft speed, so once I've established that as my base idle, it remains there. On shut down I use the rocker to reduce to low idle again for the next start up.

Thanks for posting this. I had no idea that Allison even had a recommended rpm for input shaft speed. I'll look it up and set my base idle RPM accordingly.

I spoke to the cummins factory rep at Newmar today and he said that 1000 RPM for high idle is fine. So I think I'll leave the high idle there. Also, since the engine ramps up to 1000 RPM if I hit the high idle right away, I'm thinking that the computer probably checks oil pressure before ramping up. But I'll check that as well.

ON EDIT: I just looked up the low idle speed in the Allison 4000MH manual and it says it's between 500 and 800 RPM. Cummins recommended 650 which is exactly between the two so I think that's a good setting.