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

 

[Gary Fowler]

I gotta pose one other thing for the group to consider. Wouldnt the coolant still have some flow due to natural convection with hot fluid rising and cooler fluid being sucked in from the bottom of the radiator as long as the thermostat was opened, I think you would get a bit of circulation. Maybe not much but enough so that the radiator would disipate some engine heat after shut down.

 

[RoyJackson]

I gotta pose one other thing for the group to consider. Wouldn't the coolant still have some flow due to natural convection with hot fluid rising and cooler fluid being sucked in from the bottom of the radiator as long as the thermostat was opened, I think you would get a bit of circulation. Maybe not much but enough so that the radiator would dissipate some engine heat after shut down.

Maybe some movement...but would it be enough? Well, I'm not going to experiment with an engine that costs $3000-$4000 to rebuild. Not to save 10 cents worth of fuel...

To the guys who shut down immediately...I read an article (review) of the new Porsche Cayenne (sp??) which shuts down almost every time you stop (fuel economy and air pollution reasons). I wonder how they handle "heat sink"? (my guess is an electric pump keeping the coolant flow going...but that's just a guess).

 

[ModMech]

If you shut down a HOT engine, the thermostat will remain open until the coolant cools to below the "start-to-open" temp. This will *allow* some convective flow thru the radiator but because hot air/water rises the flow will be very limited.

MANY vehicles are shipped with full or semi-synthetic oil from the factory, the Corvette is on long-time example with many other high end vehicles as well. The Ford GTs, Lightnings, Cobras ALL get full or semi-synthetic oil at the plant. Saying the use of synthetics will harm the engine is 100% false, period.

One of the biggest factors in CHT is EGT, when you lean out a gas engine EGTs go up and fast. When you land an airplane with a carb, it is LEAN because the air is much more dense at ground level than at 5,000 ft. Add to that the fact that airflow is greatly reduced at 50 mph compared to 120 mph and it is easy to understand increased CHT/EGT after landing.

The main point is, if the engine is HOT it will not hurt anything to idle a little before shut-down, but if it is cold then you are doing more harm than good!

 

[ray66v]

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.

No, I did not say that GM puts synthetic oil in everything. If your trying to hold down prices, that would not be a smart move.

I was making the point that GM is selling brand new cars, with synthetic oil in the engine. So are other manufacturers.

It's 2010 now. The additives in mineral oil toady make it so good, the lubricity test results on mineral oil, and synthetic oil are almost identical, so the parts are not going to "wear in" any different.

When an engine is designed to "wear in" a special breaking oil is specified, and supplied, for that purpose, I believe Deere has some equipment that still uses a breaking oil.

The only difference between synthetic oil, and mineral oil today is the synthetic oil holds up better in extreme temperatures, and can last longer as a result.

So, you can use synthetic in new equipment.

I have no doubt however, some will never accept that fact.

The following is a partial list of cars that are, or were, shipped with synthetic oil from the factory. If you don't agree with any of them, take it up with Mobil oil, it's from their web site:

> Acura RDX
> Aston Martin
> All Bentley Vehicles
> All Cadillac Vehicles
> Chevrolet Corvette C6 and Z06
> Chevrolet TrailBlazer SS
> Chrysler 300C SRT-8
> Cobalt SS S/C Coupe
> Dodge Caliber SRT-4, Charger SRT-8, and Magnum SRT-8
> Jeep Cherokee SRT-8
> Mercedes-Benz AMG Vehicles
> Mercedes SLR
> Mitsubishi Evolution
> Pontiac Solstice GXP
> All Porsche Vehicles
> Saturn Ion Red Line and Saturn Sky Red Line
> Viper SRT-10

The thinking that you cannot use synthetic oil in a new engine goes back to the very early days of synthetic oil many decades ago.

In the mean time, this myth is still spread, so it continues to be considered true.

 

[ray66v]

Is it a case of cooling the turbos or allowing oil to flow through the turbo bearings?

Many believe the oil in the bearings of the turbo will cook, if the cool down period is not utilized.

Some aircraft manuals apparently were published with this procedure in them.

As I said, this was debunked.

The turbo is never gets any cooler than it is on touch down.

Like the synthetic oil in new engines myth, many refuse to accept that it as incorrect, and still use a 5 minute clock after landing, before shut down. :confused3:

 

[RoyJackson]

Many believe the oil in the bearings of the turbo will cook, if the cool down period is not utilized.

Some aircraft manuals apparently were published with this procedure in them.

As I said, this was debunked.

The turbo is never gets any cooler than it is on touch down.

Like the synthetic oil in new engines myth, many refuse to accept that it as incorrect, and still use a 5 minute clock after landing, before shut down. :confused3:

Well, at this point, all we have is your post. Why not provide a link to a reputable study backing up your assertions?

 

[Transit]

I gotta pose one other thing for the group to consider. Wouldnt the coolant still have some flow due to natural convection with hot fluid rising and cooler fluid being sucked in from the bottom of the radiator as long as the thermostat was opened, I think you would get a bit of circulation. Maybe not much but enough so that the radiator would disipate some engine heat after shut down.

You are only looking at the water-engine coolant. Oil is also a coolant and only cools when circulating removing heat deep within the engine.

 

[TripleR]

I simply cannot draw a conclusion that what is good/bad for an airplane is good/bad for my turbo tractor, so I will continue to follow the manual printed by the people who designed and built it and follow a cool down procedure.

I AM NOT saying anyone is wrong, I am just uncomfortable drawing such a correlation absent apples to apples comparison.

 

[ray66v]

Well, at this point, all we have is your post. Why not provide a link to a reputable study backing up your assertions?

I was unable to find the article on line, or I would have done so.

I did not think anyone would be interested enough in flying, to spend a lot of time looking for it.

I am going to the airport today, I will see if anyone has it. It was several years ago, so it is not going to be on the top of anyone's pile.

There was considerable discussion about it in our club at the time. So, if you check in your inner circle, you probably can find people who are aware of it.

I will post a link if I can.

 

[whodat526]

However, the coolant flows stops once the engine is shut down and the thermostat had been open since the engine got to operating temperature.
So, you still have the heat sink situation.
As far as my road vehicle, I don't run the engine hard except when merging on to a highway. Even then, I shift (manual transmission) 1000-2000 RPM below redline. So, it doesn't really get that hot...and ambient (outside) temperature doesn't affect the operating temperature of an engine too much.

At this point, I'd say the guys who shut down immediately will continue to do so..and the guys who idle for a few minutes will also continue to do so. Furthur posts (n this thread) will likely be reiterations of earlier posts.
Not too much use continung...

1000-2000 rpm below red line in a car is 1-2000 rpm above what most tractors will even rev. up to they don't go but to the most is 2800 to 3000 most modern days cars will do 6000-7000 so how haven't u been running it hard as to the tractor and coolant does stop flow when it shuts down the thermostat still opens and closes it has nothing to do with the tractor running and u need to stick a thremo temp. reader to your tractor after running it mowing for a hour then to your car motor after running it down the interstate and 70 for a hour and tell me which gets hotter i know which will get hotter and if everything is to specs on the head and is running at normal temp which means not running it with the thermostat stuck or low on water it will not warp nothing i have ran many many when i say many i mean many tractors in my life and have never warp a head unless the tractor ran hot and blowed the head gaskett which in turned made the bolts not hold to spec thats the only way u will warp a head or block