Why idle before shut off?

[RoyJackson]

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...(edited for brevity)

Well, I'm not gonna convince you...so this still applies:
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...

Comes to a point where folks just got to agree to disagree...we have reached that point.

 

[Qapla]

I was taught (Dad) to always let an engine idle down for a minute or so before I shut it off. My neighbor will be at full throttle, drive over to talk and just shut it off. He starts it back up the same way. Engine racing and off he goes ...

Keep in mind this was the original post. After reading it again, I saw no mention of his neighbor "driving over" in an airplane, sports car, semi-truck or turbo-charged anything. In fact, he never said his neighbor was on a tractor. He may be on a riding lawn mower.

We now have 65 replies (mine makes 66) taking up 7 pages on this topic and still no real answer for the OP.

Like Roy Jackson said "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." and I tend to agree with him.

With sympathies to harpoonalt I do not think there will ever be an answer to this question. It is kinda like asking what the best color for a tractor is - too many opinions

 

[Ken_CT]

If I ever want to get onto the front porch, I am going to have to start to post more often.. so here goes.

I was under the impression that you should not use synthetic oil for break in, but this may have changed as these pictures are of an older bottle of Red Line oil, but it states "Not for Break-in of engines - Allow 3000 miles".

On the OP, the way I understand it, if you turn off a hot running engine without letting it idle to cool down a bit, the engine continues to spin through a couple of cycles, drawing in the air/fuel mixture, compressing it, but not igniting it,(no power stroke) then exhausting this mixture into a very hot exhaust, which causes it to ignite, thus a backfire. If the engine is idled to let it cool before shutting it down, the exhaust is not hot enough to ignite the mixture so it does not backfire.

 

[ray66v]

Oil temperatures may still be high during a landing, especially if you came in under power with a prop reversal.

Do you know of a gas engine you can reverse the props on?

 

[Don87]

Well, I'm not gonna convince you...so this still applies:
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...

Comes to a point where folks just got to agree to disagree...we have reached that point.

I'm old school, I've seen what happens(taken too many engines apart).............I'll let my engine rest.

 

[Qapla]

I think one of the factors that has led to people turning things off without idling first is the seat safety switch on riding lawn mowers.

People have gotten used to getting off the mower to open a gate or whatever and not thinking about the seat switch. When they get up, the mower stops running. When they get back on, they start it back up.

Since many of the cheaper models wear out before the engine dies from this practice, they assume that the sudden off/on had no effect on the motor.

When you talk about "cooling" an engine down at idle, it does not always mean that you have to run the machine for several minutes at idle to cool it down.

For our cars, most of us do not fly into a parking space at highway speed then kill the motor while it is still racing. We slow down, turn in, park, take it out of gear and turn it off. This has the effect of cooling it down.

For a small gas engine like a lawn mower, just returning it to idle before killing it may be enough for the excess heat to dissipate.

Common sense will cool most engines enough for a shut down.

 

[MossRoad]

Several people have made comments about washing oil off of the cylinder walls by introducing fuel into the cylinders at shutdown....

That would imply there is oil ABOVE the piston rings. If that is the case, how can cars go through thousands of start/stop cycles between oil changes, for well over a hundred thousand miles, and never use a drop of oil???

If the cylinder walls are getting coated with oil above the rings as many people say, why is none consumed???

 

[MossRoad]

As for air cooled engines, such as those found on lawnmowers, like Kohlers, Brigss, etc... many of those are meant to be run at 3600 RPM all of the time. Full RPMs provides not only proper oil circulation, but it also turns the fan at the proper RPM to cool the engine.

 

[zman007007]

What? Where the heck did you get that idea?

where you said if you have a manual choke use that to shut engine down. zman

 

[zman007007]

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

Thanks Spyderlk, exactally what I meant. gas being thinner than oil is going to seep past that top ring I believe and wash off any oil that was left below the ring, especially on an older engine. Also why do you not see more people pull into a parking space, hold the throttle to the floor and then turn their engine off, just wondering? LOL zman :confused2:

 

[Don87]

Thanks Spyderlk, exactally what I meant. gas being thinner than oil is going to seep past that top ring I believe and wash off any oil that was left below the ring, especially on an older engine. Also why do you not see more people pull into a parking space, hold the throttle to the floor and then turn their engine off, just wondering? LOL zman :confused2:

Actually if one thinks about it.............it may be worse on a newer engine.
On the old engines, gas was introduced through the intake manifold via the carb........newer engines introduce the fuel through an injector, which goes into the cylinder, via a spray nozzle.
Which could could cause cylinder wash quicker.............a dribble from the intake.......or a spray from an injector?

 

[SPYDERLK]

Several people have made comments about washing oil off of the cylinder walls by introducing fuel into the cylinders at shutdown....

[That would imply there is oil ABOVE the piston rings. If that is the case, how can cars go through thousands of start/stop cycles between oil changes, for well over a hundred thousand miles, and never use a drop of oil???

If the cylinder walls are getting coated with oil above the rings as many people say, why is none consumed??? ]

How thick a coating do you envision? How would you detect an oil level a drop low -- or even a couple hundred?
larry

 

[whodat526]

I
For our cars, most of us do not fly into a parking space at highway speed then kill the motor while it is still racing. We slow down, turn in, park, take it out of gear and turn it off. This has the effect of cooling it down.

Common sense will cool most engines enough for a shut down.

just do me one favor when u go to get out of your car after driving it for about thirty minutes and drive it normally before u pull in the parking lot look at the temp gauge when u put it in park look at the temp gauge and right before u shut it down look at the temp gauge i bet u dont see no change at all because there is not any

 

[whodat526]

Thanks Spyderlk, exactally what I meant. gas being thinner than oil is going to seep past that top ring I believe and wash off any oil that was left below the ring, especially on an older engine. Also why do you not see more people pull into a parking space, hold the throttle to the floor and then turn their engine off, just wondering? LOL zman :confused2:

if oil is on the cylinder walls above the piston rings u should overhaul that motor oil shouldn't be above the rings that is what the oil ring does clean the cylinder walls free of oil or it will some think of that please and the oil ring is the very bottom ring there will be three rings or more on each piston

and nobody pulls into a parking space and holds the throttle to the floor so u really think when u let of the throttle that cools the motor down right then and there wrong look and the temp gauge it doesn't move

think about what ur saying is u can boil water and then turn off the stove and that water will be cooler if thats the case make a vid of u boiling water and then cut it off and stick ur hand in it and lets see what happens
because this is all the same concept here

 

[Don87]

How thick a coating do you envision? How would you detect an oil level a drop low -- or even a couple hundred?
larry

That's the part that most people don't understand.

 

[Don87]

just do me one favor when u go to get out of your car after driving it for about thirty minutes and drive it normally before u pull in the parking lot look at the temp gauge when u put it in park look at the temp gauge and right before u shut it down look at the temp gauge i bet u dont see no change at all because there is not any

Do your check at 3 to 5 minutes.............not 30.
We will be waiting for your response!
Any engine...........I don't care who drives it, will heat up after shut down.
It doesn't matter how easy you drove it, whether it is air or liquid cooled........that's the nature of the beast.
There are ways to combat nature, but it will eventually overtake you.

 

[whodat526]

Like Roy Jackson said "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." and I tend to agree with him.

With sympathies to harpoonalt I do not think there will ever be an answer to this question. It is kinda like asking what the best color for a tractor is - too many opinions

everybody will do what they wont they have the right to sense they paided for it wether right or wrong

and the best color for a tractor is bright bright yellow lime green with hot pink racing stripes

 

[whodat526]

Do your check at 5 minutes.............not 30.
We will be waiting for your response!

well in five minutes the thermostat most likely wont even open it has got warmed up yet so nothing should be hot

 

[MossRoad]

if oil is on the cylinder walls above the piston rings u should overhaul that motor oil shouldn't be above the rings that is what the oil ring does clean the cylinder walls free of oil or it will some think of that please and the oil ring is the very bottom ring there will be three rings or more on each piston

and nobody pulls into a parking space and holds the throttle to the floor so u really think when u let of the throttle that cools the motor down right then and there wrong look and the temp gauge it doesn't move

think about what ur saying is u can boil water and then turn off the stove and that water will be cooler if thats the case make a vid of u boiling water and then cut it off and stick ur hand in it and lets see what happens
because this is all the same concept here

Some punctuation might help you make your points better.

 

[Don87]

well in five minutes the thermostat most likely wont even open it has got warmed up yet so nothing should be hot

We might be misunderstanding each other, or I read the original post wrong.........Run the vehicle for a while, park it, note the temp, shut it down..................turn the key on after 3 to 5 minutes..............note the temp..........there will be a significant increase in temperature.