Why idle before shut off?

[whodat526]

and his tractor will probably last longer

 

[johnrex62]

My manual says to start the tractor with the throttle about mid position. I have always allowed it to warm at this speed a few minutes before doing anything. I have also let it sit after driving back to the shed at this speed before shutting it off.

Would I be better off putting the throttle at the lowest position to cool down, or is the mid point better due to the increased coolant flow at the higher throttle? I am making an assumption that the faster engine speed translates to a faster pump speed and thus more flow, please correct me if I am wrong about that also.

 

[TripleR]

My manual says to start the tractor with the throttle about mid position. I have always allowed it to warm at this speed a few minutes before doing anything. I have also let it sit after driving back to the shed at this speed before shutting it off.

Would I be better off putting the throttle at the lowest position to cool down, or is the mid point better due to the increased coolant flow at the higher throttle? I am making an assumption that the faster engine speed translates to a faster pump speed and thus more flow, please correct me if I am wrong about that also.

I will be interested in what the experts say about this also. On non turbo, I consider my trip to the barn enough of a cool down as the engine is not under load and no matter how long I run it, it really isn't going to get any cooler. Of course this depends on how long your barn/shed is from your work site. Mine is five minutes or so to thirty.

For cool down, I run mine at idle.

 

[Transit]

My instructions said to let it low idle for 5 minutes after working before turning off on hot days, so thats what I do. They also say on cold days let it low idle for 5 minutes before starting work, so thats what I do.

When you start a cold engine why do you let it idle? To stabilize the temperatures and let the components expand uniformly, the oil is brought to operating temperature and helps distribute heat within the engine.

Why idle a hot hard working engine? The same reason as warming a cold engine, only the process is in reverse.
The cool down allows components to return to a normal size, interior heat is absorbed by the circulating oil and coolant; valves are cooled by the lower exhaust gas temperatures. To do otherwise is to shock cool the engine.

 

[RoyJackson]

My manual says to start the tractor with the throttle about mid position. I have always allowed it to warm at this speed a few minutes before doing anything. I have also let it sit after driving back to the shed at this speed before shutting it off.

Would I be better off putting the throttle at the lowest position to cool down, or is the mid point better due to the increased coolant flow at the higher throttle?

I'd suggest you idle at 1200-1500 RPM, no lower.

 

[firefighter jim]

The cool down period I go along with, but not racing the engine (or, "blipping the throttle" as we call it).
All blipping the throttle does is allow raw gasoline to wash oil off the cylinder walls. That's a habit I lose, if I were you...

Ditto on that..............

 

[Gary Fowler]

Synthetic oil was not shipped in My Chevy Truck and I dont know where anyone picked that up. My owners manual doesnt tell me what kind of oil they put in for break in oil, just what to use when I change it and I dont believe yours does either. Every motor supplier I have ever heard of tell you not to use synthetic during a break in period. You actually want the parts to wear in together and all my operation manuals tell me not to put additives in the oil or use sythethic during break-in period. My LS manual tell me specifically not to use it and to run the tractor unde full load during the break in period and avoid excessive idle. Just as you wont see me starting my tractor at full throttle, you wont see me draining the factory oil and putting in synthetic for break in. Some things are just common sense that you know you shouldnt do and I for sure would not take the word of most salesman on something, heck they hardly know how to start them up and for sure know almost nothing about anything that is not in the sales brochure. Having said that, there are a few tractor dealerships with owners acting as salesman that may have 50 years of tractor experience, I tend to listen to those old guys to some extent but I wouldnt believe a car salesman if he said he was on fire and I saw the flames.

 

[ray66v]

I do idle my diesel to cool it down, if I have been running it hard, and it's hot.

However, sometimes, the simplest most obvious thing is not as it appears.

As an example, for decades it was carved in stone that if you had an airplane that had a turbocharger(s), you must let it run for 5 minutes after landing, before shutting the engine(s) down. This was a procedure most everyone was convinced would cool down the turbo's, and extend their life.

Being as the turbos are extremely expensive, and have been know to fail, almost no one questioned the procedure. Everyone thought at worst, your wasting 5 minutes of fuel. Better safe, than sorry.

One day, a flying publication decided that with modern testing equipment it would be easy to prove this once and for all, and determine the appropriate amount of cool down time.

Oops!, they found out that during the time the engines ran on the ground after landing, the turbo's actually heated up.

Turned out, all those years everyone was blissfully doing the exact opposite of what they needed to do. :thumbsup:

Yet, this cool down myth is so ingrained in people, many still believe it.

Sometimes you could be better off, if you don't worry about things too much.

 

[Gary Fowler]

Wouldnt you think that the reason an airplane engine heated up on the ground was because you had less air flow going over the air cooled engines. The engines do run hotter on the ground than in the air which is why you have to close off the air inlet a bit when you reach cruise altitude. I never let mine airplane engine run after I got it parked, I just leaned it out and let it die. Taxiing was plenty of idle time, of course my Cessna Cardinal retractable gear wasnt turbo-charged so I didnt worry about that end of it.

 

[SPYDERLK]

I think by using the choke to kill the engine you would be washing off any oil that would have been left in the cylinder. In other words you would be starting with a dry cylinder next time you fire it up. zman :confused2:

What? Where the heck did you get that idea?

Common sense I guess. I dont think hes saying youve got little guys with gasoline soaked scrub brushes - just that an extremely rich mixture is left in the cyl, some of which can condense and rinse oil off the walls.
larry