Go BottomRunning a Diesel at Idle
 | Ronnie Franks
Join Date: Posts: 1 
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2000-05-26 16689
Can anyone provide information about idling a diesel tractor engine? Is it okay or should it be avoided? What are the consequences? Seems like I read somewhere that it was not good for the engine but I can't remember why. Regards.
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| Bird Senter
Join Date: Jun 1999 Posts: 962 
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2000-05-26 16697
I suspect you'll get some conflicting opinions on whether, or how long, you should let a diesel engine idle. Naturally, you are using a small amount of fuel, contributing to air pollution, racking up hours on your engine, etc. On the other hand, you'll find a lot of big diesel trucks idling in rest areas while the driver sleeps, I heard one fellow say that diesel is cheap compared to starters, one of my REAL farmer neighbors has 3 air-conditioned tractors and his principle business is raising and selling hay, and when he bales hay by himself, he has the baler on one tractor and the rake on another, and he rakes awhile, bales awhile, goes back to raking, etc. and neither tractor is shut down all day. Of course, he says that's because it gets too hot in those tractors if he shuts down the air-conditioning. And I have two brothers who are tool distributors calling on mechanics so their trucks are their store and showroom, air-conditioned of course, so those trucks are not shut down from the time they leave home in the morning until they return at night. For me personally, I don't have any concern about it. If I'm going to be off my tractor for more than just a few minutes, I shut it down because it's quieter, but I wouldn't be concerned about leaving it idling either. ....
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| droz
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2000-05-27 16719
I know that my Kubota and my John Deere manuals both recommend not letting it idle for long periods. There reasoning is mainly for the lack of cooling when it is idling, especially at very low RPMs. And for the obvious wasted fuel. Starting the newer diesels is so easy now it is hard to justify idling them. ....
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| TomG
Join Date: Feb 2002 Posts: 5406 Upper Ottawa Valley 
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2000-05-28 16727
I tend to shut mine down, but the reason is more for safety. If I'm away from the tractor, there's always the chance that somebody may try to operate it. If I'm near, chances are I'm making some adjustment. With the engine running, there's always the chance that the transmission or PTO is accidentally engaged, or a hydraulic lever is bumped. Of course, hydraulic devices can be accidentally lowered even with the engine off.
I believe that diesels, unlike gasoline, engines do not have heating problems when idling. It seems to have to do with the lack of a throttle valve in diesels. There is always full air flow though the engine, varying only with the RPM. Gasoline engines operate under high intake manifold vacuum at idle due to the closed throttle valve.
Never the less, fuel combustion in a diesel supposedly is less complete when idling, and I believe oil manufacturers recommend more frequent oil changes for engines that idle a lot. I do idle mine 5 minutes or so for warm up and cool down.
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| Glenn
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2000-05-28 16734
I read on one of the nets that a diesel engine can be damaged by prolonged idling because there is insuffient lubrication. Any truth to this? ....
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| MikeC
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2000-05-28 16735
The main reason I had heard not to idle a compact diesel tractor is because of the extra carbon buildup in the combustion chambers. I guess this would follow the idea of incomplete combustion at low RPM. ....
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| John Sheehan
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2000-05-28 16748
As Paul Harvey says, "From the 'For what it's worth department'"
Again, no solid foundation, just old habits and coffee shop talk, but when ideling any diesel from my old 4020 down to my 430, I usually put it at around 800 - 1000 rpms, just to make sure the oil presure is up amd there is suffucent coolant flowing. It also appears to run a bit smoother just above idle. After working the diesel and really getting it hot I always let it cool down a bit before I turn it off. I used to run an Case 4690 that actually had a pyrometer (exhause temp) that I would watch before I turned it off. Something about when it's too hot and you shut it off, parts cool off at different rates and could cause a problem.
I think that much of these old practices of never turning off a diesel except for the night comes from old technology - ie. inefficent fuel burning, engines built to less demanding specs.
Just my thoughts ....
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| MichaelSnyder
Join Date: Jun 1999 Posts: 0
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2000-05-30 16779
Ronnie,
Also from the FWIW department, Diesels are also known as "heat engines" in that the fuel is ignited by heating the fuel/air mixture to the point of combustion. Unlike gasoline motors, which maintain a constant fuel/air ratio of ~14:1 regardless of load or RPMs....A Diesel's Fuel/air ratio will vary from ~100:1 at idle down to a miserly ~25:1 under full load. Because of ratio at idle, each cylinder is is burning so little fuel, the amount of heat generated is not enough to maintain an efficient block temperature, which will be used to heat the incoming air/fuel mixture before compression/combustion...and the process repeats.. Hence unburned fuel creates carbon build-up. Making it odd that Droz's manuals would talk about a Diesel "overheating" at idle??". ....
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| John Sheehan
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2000-05-30 16782
Michael, great points and they make sense. My experience has been that diesels will overheat if left to run too long at a low idle. Probably though it has more to do with the decreased airflow through the radiator and over the block, and the decreased coolant flow. I don;t have the problem when I idle them around 100rpms. ....
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| David Waite
Join Date: Jun 1999 Posts: 43
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2000-06-01 16828
Just wanted to put my two cents in. At idle in the past diesels unburnt fuel causes wash down thining the oil thus causing more wear on all componets. For this reason diesels due require more frequent oil changes than gas engines. ....
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