How Long An Idle Is OK?

Joe Dirt · **Posted:** Fri Jan 30, 2009 12:08 pm

I just got back From a Detroit Diesel DD15 Overhaul school and the operator guide talks about extended idling. It says "The common belief that idling a diesel engine causes no engine damage is wrong.Idling produces sulfuric acid, which is absorbed by the lubrication oil and eats into bearings, rings, valve stems and engine surfaces." It then goes on to say that if you have to idle the rpm's should be raised.

warp2diesel · **Posted:** Fri Jan 30, 2009 12:55 pm

I don't do an excess idling, but if you are using Bio or ULSD, how are you going to make enough H2SO4? If your using the old high sulfur diesel, yep it could happen, but you can't use that stuff over the road.

Last time I checked, Diesel Engines do not use any type of Nuclear Fusion Reaction, just a chemical reaction.

If we could have a Nuclear Fusion Type Reaction, I think we would need stronger cranks, rods, pistons, heads, blocks, and bolts at least :lol:

Religion offers redemption and forgiveness, but the Laws of Physics that apply to Chemistry, are not forgiving.

nursecosmo · **Posted:** Fri Jan 30, 2009 6:53 pm

warp2diesel wrote:

I don't do an excess idling, but if you are using Bio or ULSD, how are you going to make enough H2SO4? If your using the old high sulfur diesel, yep it could happen, but you can't use that stuff over the road.

Last time I checked, Diesel Engines do not use any type of Nuclear Fusion Reaction, just a chemical reaction.

If we could have a Nuclear Fusion Type Reaction, I think we would need stronger cranks, rods, pistons, heads, blocks, and bolts at least :lol:

Religion offers redemption and forgiveness, but the Laws of Physics that apply to Chemistry, are not forgiving.

Amen! Operation manuals can seldom be considered as the ultimate word in correct vehicle maintenance and function. The advice given was sound but the reason given was not.

BBB · **Posted:** Sat Jan 31, 2009 9:49 am

Too bad the CRD Liberty is fly by wire. I always use high idle devices on the 2 ton trucks when available. My favorite is the adjustable knob style on the dash. It really gives the vehicle a tractor/ generator like usefullness with a PTO. Others are ambient temperature automatic like on my Dodge Ram, or switch activated, but usually yeild a 1000-1250 RPM engine speed. I would think that would keep operating temperatures high enough to prevent cylinder wash. I cannot safely recommend the use of a high idle throttle stick formally known as a throttle set to artificially increase the idle speed on a vehicle... although I use them. If equipped with electric seats you have a nice variable high idle set up when a stick is placed between the seat frame and the throttle peddle (safety awareness disclaimer) Others use a notched stick cut to lenght that wedges between the bottom of the dash and the throttle peddle (safety awareness disclaimer) I have noticed that sometimes the automatic idle control trys to compensate for the high idle and once you go above a certain high idle RPM the engine will rev.

So where's the PTO attachment point on the Liberty tranny? :roll:

Do any of the VM 2.8's used in industry have high idle controls and if so is PCM or ECM enablable?

Here's a throttle set: http://www.12volt-travel.com/truck-auto ... 9_662.html
And if we had a standard throttle cable: https://zips.com/Store_schematics.aspx?CAT=60&SCHEM=47

warp2diesel · **Posted:** Sat Jan 31, 2009 11:24 am

Aren't most if not all of the trucks with PTO attachments manuals?
If the accelerator is controlled by a Potentiometer as stated in the Service Manual, you could install a DPDT switch and install another Throttle Control Potentiometer to over ride the accelerator pedal. Placing a small cable with a tension spring to trip the switch back to accelerator would be a brain dead way to deactivate the Throttle Control Potentiometer.

Put it in a kit and you can sell $10 worth of parts for $150

yakers · **Posted:** Sat Jan 31, 2009 2:18 pm

warp2diesel wrote:

Put it in a kit and you can sell $10 worth of parts for $150

That forked stick for $0 sounds even cheaper. Is that better than a brick?

Sir Sam · **Posted:** Sun Feb 01, 2009 8:06 pm

BBB wrote:

Too bad the CRD Liberty is fly by wire. I always use high idle devices on the 2 ton trucks when available. My favorite is the adjustable knob style on the dash. It really gives the vehicle a tractor/ generator like usefullness with a PTO. Others are ambient temperature automatic like on my Dodge Ram, or switch activated, but usually yeild a 1000-1250 RPM engine speed. I would think that would keep operating temperatures high enough to prevent cylinder wash.

Lucky for us since the liberty is drive by wire you could wire in a very simple bit of electronics(even using a rotary knob attached to a POT to adjust a high idle).

railguy · **Posted:** Fri Dec 25, 2009 5:01 pm

I'll start off by saying that I don't like letting any engine idle for extended periods unless it is necessary--it just wastes fuel. That said, there can be circumstances where extended idling is necessary. Back when I got my '05 CRD, I was confronting the possibility of having to use it as a "mobile office" on occasion for 6-8 hours at a time in subzero weather conditions--in that circumstance, extended idling would be necessary. So, I consulted a couple of knowledgeable people about it. First was my long-time mechanic--he maintains numerous fleets of light-duty diesel vehicles for government agencies, utilities, and railroads. (I have used his services for years, as I also have a GM 6.5 diesel.) His thoughts were that the "wet-stacking" issue is generally overblown--he has seen very little engine damage from wet-stacking over the years in most light-duty truck diesel engines, unless they are regularly idled for extended periods in temperatures well below 0° F. In the CRD's case, his opinion was that the viscous heater would keep the engine within a high enough temperature range to prevent wet-stacking in any but the most severe cold.

The second individual I spoke with was a Chrysler engineer who had worked plenty with the 2.8 CRD. He basically said the same thing about the viscous heater. He also added that the 2.8 CRD engine heritage as a tractor engine meant that it had been designed with extended idle cycles considered likely in its tractor application. So, he didn't see a problem, either.

As it turned out, about the longest that I've ever had to let my CRD idle was 1 1/2 hours in real cold temperatures--it suffered no ill effects.

A sidebar note concerning railroad locomotive idling. Those locomotive diesel engines ("prime mover" in railroad parlance) are designed for long idle cycles--they often have to remain idling for operational considerations (maintaining air brake line pressure, etc.). Also, for many years the EMD (formerly owned by General Motors) prime movers used engine seals incompatible with anti-freeze--they had to use straight water, so could not be shut down in subfreezing temperatures. The railroad mechanical people also felt that frequent heating and cooling of those huge engine blocks was not good. So, the prime movers were generally left running almost continually between overhauls. By the way, most all EMD diesel prime movers are 2-cycle engines with a combination supercharger/turbocharger, while General Electric prime movers are 4-cycle engines with just turbocharging.

Today, locomotives have myriad electronic controls that monitor all kinds of things--coolant temperature, ambient temperature, locomotive operating demands, etc. Most newer locomotives have automatic idle control and automatic start-up/shutdown that will modulate idle speeds to keep prime mover temperature even, while minimizing fuel use. If ambient temperatures and other parameters are within prescribed ranges, the computer will shut down the prime mover entirely, restarting it if one of the parameters falls outside of the prescribed range.

For their size, those locomotive prime movers actually use fairly little fuel at idle. Considering that the current models have cylinder displacements between 710 and 900+ cubic inches PER CYLINDER (that's between 4 and 5.5 CRD's per cylinder) in V-12 and V-16 models, there fuel usage at idle is pretty low, at between about 2 1/2 and 4 1/2 gallons per hour when idling continually.

geordi · **Posted:** Sat Dec 26, 2009 1:20 am

Wow... Zombie thread back from the dead! :frankie:

Cool info on the train stuff. In another life, I might have done that instead of theatre.

While last winter (Soon after the most recent old reply in this thread) my engine decided to cash in it's #1 cylinder on me, that had NOTHING to do with any of the extended idling I had done on it. I have traced it down to the most likely causes of either incorrect oil weight for the temperature (I honestly cannot recall what weight was in it at that time, it might have been 15w-40) OR the failure of the turbo releasing too much pressure from the oil lines that also DIRECTLY fed the #1 cylinder.

I'm less than impressed by that oil passage routing, I personally would have set the system up as if the turbo was "cylinder #5" in some way so that the cylinders would not starve for oil in the event of a catastrophic loss of the turbo's oil line... Which is exactly what happened on mine. Without a boost gauge or EGT gauge, I had no real knowledge of what had transpired when the shaft snapped.

In other news, I will be driving 1000 miles in a few days, and fully plan to only shut the CRD off once during this trip: When I stop in the middle for the night. If I didn't have a place to stay already available, the CRD would be my hotel and I am confident that the thermostat AND the coolant heater would both be quite effective in keeping the temp gauge within one tick of the center... Which is exactly where it is when I'm driving on the highway. So if the cylinders aren't "washing" with fuel when driving... They shouldn't when I'm idling either. And if they were... Wouldn't I see the evidence as a RISING on the dipstick level? None exists, the level is static between changes.

As always, YMMV, but I'm happy with my own 'Prime Mover' tractor. :wink:

railguy · **Posted:** Sat Jan 16, 2010 8:10 pm

My Christmas present this year was a ScanGuage II, so I've been doing a little experimenting with it. For purposes of this thread, I was looking at fuel use at idle, comparing the CRD to some other vehicles. The vehicles: 2005 Liberty CRD, Toyota Camry with 2.4L gas, '98 Jeep Cherokee with 4.0L gas, and '96 GMC with 6.5L diesel. The following should be noted--the Liberty CRD has had all of the recall flashes done, which is supposedly necessary for the ScanGuage II to operate correctly on the CRD. The ScanGauge is not listed as compatible with the '96 GMC 6.5, but I appeared to get accurate readings, with one possible exception, which I will talk about later. Excepting the CRD (because it is garaged), the tests were all made from cold starts at outside ambient temperatures below 15° F. The vehicles were idled long enough after starting to scrape the windows of frost, generally around 5 to 7 minutes, then driven moderately (under 30 mph) until they reached operating temperature.

One of the chief advantages of a diesel is its much more efficient fuel combustion and lower fuel usage at idle compared to a gas engine. The CRD comparsion is interesting in that regard.

First, though the Jeep Cherokee's results. The Cherokee was started at 9° F. Its fuel usage at startup was a whopping 1.87 gallons per hour (gph), which dropped to 0.70 gph at full operating temperature. The Cherokee reached full operating temperature the fastest of all of the vehicles--taking about 10 minutes to reach a coolant temperature of 197°.

Next, was the Camry. It shows how far fuel-injected gasoline vehicles have come in idling fuel economy in the last 10-15 years. Ambient temperature at startup for it was 11°. Its fuel usage at startup was 0.76 gph, which dropped to 0.21 gph at full operating temperature. It took about 17 minutes to reach full operating temperature of about 185°.

The GMC was an interesting story, especially when one compares it against the Liberty CRD. I do question the gauge readings on it. Ambient startup temperature was 15°. At startup, its fuel usage read 0.64 gph, less than the Camry and only about a third of what the Cherokee was using. After 15 minutes, engine temperature had only reached 143°, and took nearly a half hour of in-town driving to reach 185°. Fuel usage dropped, however, to 0.14 gph after only 10 minutes, and reached a low of 0.10 gph after 15 minutes. This seems ridiculously low for an engine of 6.5L displacement, but if the fuel usage is accurate, it would explain why the engine was so slow to warm. I did have the thermostat checked, and it was functioning normally. Another interesting anomaly found with both the GMC and CRD was that putting the transmission in gear and putting the engine under only that load increased the fuel usage considerably--going from 0.10 gph to 0.48 gph in the GMC. On the gas engine vehicles, putting the vehicle in gear had a minimal effect on idle fuel usage.

Finally, the CRD. Unlike the others, it was started at an ambient temperature of 57° in a garage. Initial fuel use, with the viscous heater operating, was 0.56 gph. The outside ambient temperature was 30°. This fuel usage remained about consistent until the coolant temperature reached around 155-160°, at which point the viscous heater likely shut off. Then fuel usage immediately dropped to about 0.15 gph. Like the GMC, putting the vehicle into gear would immediatly bump the fuel usage to about 0.48 gph. Like the GMC, warming times to operating temperature were longer than for the gas engines, even with the viscous heater on the CRD.

There are still a lot of questions. Why would the CRD, with an engine way less than half of the displacement of the GMC 6.5, use about the same amount of fuel at idle? Is the GMC figure inaccurate, or does the absence of all the emission control hardware on the GMC that is present on the CRD make it just that much more efficient at idle than the CRD? If the figures are to be believed, then when the viscous heater runs, it negates much of the efficiency advantage of the CRD at idle compared to a similar displacement gas engine.

I also did an experiment on to see what effect an extended idle would do to the engine temperature on the diesels. On a 15° day, the GMC maintained operating temperature, only cooling about 3 degrees after idling for nearly 30 minutes. I attribute this to the large mass of the 6.5 block. On a day nearly 20 degrees warmer, the CRD slowly lost temperature for about 10 minutes, after which the viscous heater apparently began cycling to maintain engine temperature. The gph would bump from 0.15 to about 0.40 with no change in engine RPM. Apparently, the engine computer senses the load on the engine and increases fuel flow in order to maintain the same engine RPM with the viscous heater load on the engine. The system did operate as intended, maintaing coolant temperature within less than a 10 degree range over nearly 30 minutes of idling.

All in all, an interesting experiment. I concluded that for short trips in cold temperatures, the Camry is probably the best and most efficient choice, which is not what I expected. At the other end of the spectrum, the 4.0L Cherokee should not be idled at all if one is concerned about fuel economy. Once at operating temperature, either the GMC or the CRD are pretty efficient idlers as long as it is warm enough that the viscous heater on the Libby doesn't have to run constantly. This is sort of an ongoing experiment. I am going to contact ScanGauge to see if the readings I'm getting on the 6.5 are bogus. That fuel use at idle for that engine just seems way too low.

geordi · **Posted:** Sat Jan 16, 2010 9:06 pm

Very interesting, and a great write-up!

I'm intrigued to see your future results, although I do have to say that the diesel fuel usage seems to track, and explains a bit about the viscous heater based on my own observations.

Summer of 2008, I drove to New Hampshire and idled my CRD overnight while I was sleeping in it at a NJ service plaza with the rest of the truckers. I filled it (Ok, they filled it) before I drove over and parked, then filled again in the morning. It took 2 gallons exactly, for 8 hours of idling. This was with the AC on all night, and the parking lights. So there was a bit of load on the engine. That puts it at .25 gph, which makes sense, considering the VH is smaller than the AC compressor. I've heard that the AC can draw as much as one full HP to run on other vehicles, not sure about ours.

My VW Jetta was idled in the same way when I owned it, and performed about the same - .2 gph with the AC on, for a 1.9l 4cyl diesel.

Do you have a GDE tune? It would be interesting to compare, especially with the ability they have to control the VH's operating temps. Likewise, it would be interesting to see exactly what the temps do if the grille is completely closed off, or only has one chamber left open for the fan. The engine fan never really stops, but can the thermostat retain enough heat without the VH and airflow...?

Rich · **Posted:** Sun Jan 17, 2010 12:15 am

There is NO reason to "beat the heat of the day" anywhere in North America with A/C. Drink water, keep excess activity to a minimum, take breaks, and enjoy the fact that you are NOT wearing body armor, helmet, long-sleeves, and pants. "Escaping" to A/C will actually do more harm than good.

railguy · **Posted:** Sun Jan 17, 2010 12:45 am

I don't have the GDE tune, but I am considering it. A few other general notes about the vehicles. I've had the Cherokee for years. It will actually get 19-25 mpg on the highway if driven sensibly--toward the lower figure now since I have it lifted with pretty aggressive 31/10.50/15 tires. Take it off road where there is a lot of low speed idling and it will drop to the 10 mpg range, though. The CRD will get 25-30 mpg on the highway--again toward the lower range now, since I have also put the Frankenlift II on it with bigger tires. Off-road, it will get up to 15 mpg--50% better than the Cherokee even though the Cherokee weighs about 800 pounds less. I keep the Cherokee for arduous off-road work and that is the main use that it sees. The CRD, now that I have it lifted, is quite off-road capable (its stock low clearance and soft front springs made it near useless for anything but mild trail work before I installed the Frankenlift), but I don't like to beat it up unnecessarily when I have the Cherokee for that kind of hard use.

The 6.5 is the family "beater" truck. It gets about 19 mpg on the highway if one keeps the speed under 65 mph. Jump it up to 75 mph and the mileage drops to about 16-17 mpg. Off road, it will manage around 13 mpg, which is almost double the off-road mpg I got years back with a carbureted 350 gas V8 in a 4WD pickup. My long-time mechanic, who specializes in diesels, has an '06 Duramax which he has regularly clocked at 22 mpg on the highway. Interestingly, the smog controlled 2008 and newer Duramax's otherwise identical to his are only getting around 15-16 mpg at best, according to his fleet customers.

The Camry is my daily driver--I've gotten as high as 42 mpg on the highway with it on trips where my speed stayed 65 mph or under. Typical highway mileage is in the mid-30's, with in-town usually in the low 20's .

I should add that a lot of my highway driving is mountain driving over passes up to 11,000 ft. elevation, and all of my driving is over 4,500 feet elevation. For that kind of driving, those turbodiesels are really nice, though the Camry does OK for a naturally aspirated 4 cylinder gas vehicle. For its engine size and vehicle weight, the CRD just performs amazingly in mountain driving while still getting very good fuel economy, and that is a main reason that I bought it.

geordi · **Posted:** Sun Jan 17, 2010 3:07 am

42mpg in the Camry... But how is it's off-road performance? :dead:

Tinman · **Joined:** Mon Apr 10, 2006 10:45 am **Posts:** 308

OK green diesel: here's a project for you. High idle feature. The later model Dodges have a DRB activated high idle that uses the cruise control. In park, turn on the cruise and set it goes to 1200 rpm. You can use the accel and coast to adjust from 1200-1500rpms. OR, Turbo Tim could come up with a box to put in the APPS circuit that is a variable idler. I have one on my 01 Ram that was made by practical diesel solutions (a basement vendor that is out of business now I think). It is a plug and play box on the dash with a rotatory knob to adjust idle. It is amazing how much I used these to idle up. Cold starts, running the A/C for the dogs in summer or running my engine driven air compressor on the 01 Ram (I went with electric air on the 06). I would LOVE to have a high idle for the Libby.

BBB · **Posted:** Sun Jan 17, 2010 4:25 pm

I 2nd the motion for a GDE value added high idle feature! That would really sweeten the deal for me. The prop rod/ wooden stick thing is getting old. That would be so cool to be able to raise the idle with the cruise controls when needing to run appliances (12 volt blenders, inverters, ect ) :5SHOTS:

railguy · **Posted:** Sat Jan 23, 2010 1:07 pm

I corresponded with the ScanGauge folks. They confirmed what I suspected--the readings on the 6.5 idle were bogus. Apparently, the ScanGauge can not process some of the parameters from the 6.5 computer correctly. The gallons-per-hour reading appears to be accurate so long as the transmission is in gear. Put the tranny in Neutral or Park and the ScanGauge misreads. At idle in gear the ScanGauge reads at around 0.48 gph which, comparing with the CRD, seems logical. That would likely drop to about 0.35 to 0.40 gph in Park which would seem logical. It would be interesting to know what the 4.8-6.0L V8's in full-size trucks use for fuel at idle, as well as the various diesels (Powerstroke, Cummins, and Duramax).

As for the tongue-in-cheek comment about off-roading a Camry, it is certainly no off-road vehicle. But, I considered the Liberty an absolutely marginal 4WD for anything but the mildest off-roading until I got the Frankenlift II installed on it, which cured its pathetic stock ground clearance.

flman · **Posted:** Wed Jan 27, 2010 6:37 am

yakers wrote:

How long can a KJ CRD idle without a problem? I expect to spend some days camping in the desert and I am trying to figure out if i can just run the CRD for its air conditioner for some time during to get through the heat of the day. This would be for maybe 1 to 3 hours. I don't think the engine would overheat but would there be any other wear issues form long idles? I am not concerned about fuel use and there would be no other load on the engine. I could also keep the RPMs a bit above idle if that is a better solution. It would certainly be quieter above idle.

I would not worry about idling any diesel, as long as the engine temp does not drop below the setting of the coolant thermostat.

How Long An Idle Is OK?

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