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K532/582: Why the fast idle?

829 views 7 replies 7 participants last post by  motiv8 
#1 ·
The service manual for my JD 400 calls for 1700-1900 rpm as the idle speed. Can anyone help me understand why it should be so high? Most of the time I don't need a reason to set things to spec, I just do it. But this thing is bugging me. What would be the downside of setting the idle at 1200? Actual operating time at idle is only a fraction of total time on the engine, and its not like I've got an A/C compressor hanging on it. Does the charge pump need a minimum speed? Would I be asking for trouble if I gave in to the lure of the slow purr?
 
#3 ·
I thought the spec idle was about 1600. Like you, I thought the high idle was ridiculous. I tend to operate at the lowest throttle setting for the task at hand and rarely over 3000. Often, with just a startup and move the tractor, I leave it at idle. At a low idle-1000 rpm or less, I found that the power steering assist didn't get enough pressure/flow to assist. So I set the idle at 1600 and have just gotten used to the higher idle. You are right that the Kohler lower idle really sounds neat.

I'm no thermal engineer but my intuition is that the cooling air need is rather linear to the operating power requirement. I'm fairly certain that the engine doesn't run cooler at 3600 rpm than 1600 given the logic that the higher fan speed moves more air. After mowing, I idle down the engine and get out the leaf blower to clean things off while the engine (in my mind) is cooling at idle. Then I drive the tractor into the shed and shut down.

I may be all wet here with my logic but through the years, I've had good luck and excellent longevity with air cooled equipment.
 
#5 ·
Grandpajay, I tend to agree with you. I tend to operate at lowest RPM for the task at hand and maneuvering that I need to do. My 44 loader rarely operates above half throttle. However hydro pumps are designed for full flow as well as the fans and slowing the speed reduces the efficiency as well as the speed at which they can be used. I tend to operate just off idle if just moving my tractor around. I also idle down after mowing as it reduces backfire if I idle for a litle while.
 
#6 ·
I am an engineer, it may have something to do with how much power is required of the engine to spin the hydraulics, or maybe the tractor gets in some sort of vibration resonance at lower rpm.

As far as lowing it, dont think there is harm in trying. If your not doing any actual work, I don't believe you will have concerns about heat. If you plan to put any load on just bump up the rpm some.
 
#7 ·
I wouldn't worry about the heat issue. Engine heat and airflow requirements are directly related to the amount of work it's being asked to do. Low speeds and high load, like mowing, are not good as the airflow may not be adequate if the governor open, allowing more air (and fuel), in order to maintain the set speed. Short, dry grass and low ground speed, no issue at all, use whatever speed you like. Tall, wet grass, higher ground speed calls for open throttle, IMO.

Idling with no load I don't think would ever be an issue to lower the speed, as long as the power steering is functional at the selected speed. My 455 doesn't work well at idle.

In other words, don't lug the engine. Good rule for trucks, tractors, just about anything.
 
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