Why idle before shut off?

[MossRoad]

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

I understand that a couple hundred drops of oil is a lot. The oil does not go past the rings. Even if it does, each stroke of combustion burns it off instantly. No worse than "washing" it off with fuel, which I do not think happens in an engine with good rings anyway. As soon as you turn off the key on a car, the spark stops, but the engine keeps spinning for many rotations, which produces suction, which sucks in fuel and air while is spins down. Fuel injected engines probably not so much, but carbureted engines for the last 80 years still sucked fuel and air after the key was turned off. Everything does not stop instantly. There is always going to be fuel and air sucked into a gas engine. I really doubt there is going to be any noticeable wear in an engine if someone gives the throttle a goose before they shut it off. I see no point in doing that, however. Seems strange to rev it up before you shut it down.

 

[Don87]

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

Wow, I missed this post.
How can I explain this.............rub to pieces of steel together at 4,000 times per minute and tell me what happens with no oil.
Yes, the oil rings on the pistons keep most of the oil in the crankcase, but think about what you said(steel against steel with no oil).
We are looking at 5 minutes tops of run time.
As far as water boiling on a stove, under heat..............that is totally different from an internal combustion engine.
The stove heats from the outside, whereas an engine heats from the inside, which will continue to generate heat, even after the shut down.

 

[whodat526]

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.

right we was both reading each others post wrong i understand that after u cut it off it sill go up some not much what is was saying in doesn't cool down by letting it idle for a minute or two before shut down that will not cool it off enough to do anything because like u state the temp will go back up after shut down no a turbo after u let it idle for about five minutes it will cool down some but it would take to long time of idling before the engine cooled any is what is was saying

 

[Don87]

I understand that a couple hundred drops of oil is a lot. The oil does not go past the rings. Even if it does, each stroke of combustion burns it off instantly. No worse than "washing" it off with fuel, which I do not think happens in an engine with good rings anyway. As soon as you turn off the key on a car, the spark stops, but the engine keeps spinning for many rotations, which produces suction, which sucks in fuel and air while is spins down. Fuel injected engines probably not so much, but carbureted engines for the last 80 years still sucked fuel and air after the key was turned off. Everything does not stop instantly. There is always going to be fuel and air sucked into a gas engine. I really doubt there is going to be any noticeable wear in an engine if someone gives the throttle a goose before they shut it off. I see no point in doing that, however. Seems strange to rev it up before you shut it down.

Actually the oil does go past the rings to a degree.


(highlighted)
That's the point.........seems strange............now think, why would it seem strange

 

[ray66v]

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

I offered that to someone as an alternative way to kill the motor, when it has a tendency to backfire.

I assume you realize that if you turn the ignition off, there is still fuel going into the engine which is not being ignited, some of which which would be by the way, if your choking it. How do you deal with the damage from that?

Since your acutely aware of engine damage, what about the damage that backfiring can do to an engine?

My 1980's vintage Briggs engine occasionally backfired, even with idle an idle down, which is why I always shut it down with the choke. It seems to run awfully well, even with all the damage it has suffered as a result of this procedure for all these years. :thumbsup:

 

[whodat526]

Wow, I missed this post.
How can I explain this.............rub to pieces of steel together at 4,000 times per minute and tell me what happens with no oil.
Yes, the oil rings on the pistons keep most of the oil in the crankcase, but think about what you said(steel against steel with no oil).
We are looking at 5 minutes tops of run time.
As far as water boiling on a stove, under heat..............that is totally different from an internal combustion engine.
The stove heats from the outside, whereas an engine heats from the inside, which will continue to generate heat, even after the shut down.

what i was saying is once it hot it will continue to be hot even if u just idle

but tell me why there is no smoke. because i know when i rebuild a engine and lightly coat the cylinder walls with oil it will smoke. the steel rings i believe or many to wear out after so long and so does the cylinder and then needs to be bored out or resleeved. i know i dont wont no oil getting past the rings on any motor i rebuild or i will have some mad customers because there will be some smoke and some blow by in the engine and will be low on compression because if oil and get by the rings so can air is all im saying

if im wrong please tell me i could be very well wrong but i believe im not and if i am i would have learned something new so dont think im being a smart*** i am just curious and dont mind being corrected i like to learn

 

[MossRoad]

Actually the oil does go past the rings to a degree.


(highlighted)
That's the point.........seems strange............now think, why would it seem strange

It seems strange because you are shutting it down so why rev it up.

As for the oil getting past the rings, any that does get past the rings does nothing to lubricate above the rings because it gets burned off. It lubricates below the rings. It gets to the top of the cylinder walls at the top of the piston stroke and is wiped off on the way down.

 

[Don87]

what i was saying is once it hot it will continue to be hot even if u just idle

but tell me why there is no smoke. because i know when i rebuild a engine and lightly coat the cylinder walls with oil it will smoke. the steel rings i believe or many to wear out after so long and so does the cylinder and then needs to be bored out or resleeved. i know i dont wont no oil getting past the rings on any motor i rebuild or i will have some mad customers because there will be some smoke and some blow by in the engine and will be low on compression because if oil and get by the rings so can air is all im saying

if im wrong please tell me i could be very well wrong but i believe im not and if i am i would have learned something new so dont think im being a smart*** i am just curious and dont mind being corrected i like to learn

Yes sir, I understand what you are saying, and I'm sure you understand what I'm saying.

There has to be some oil there, or the rings would heat up and lock the cylinder, but the "light" oil coating also keeps the 'air from entering the cylinder.
After long use(several hundred hours) the rings, and cylinder walls will wear enough to where the engine must be rebuilt to get these 'tiny' clearances back to make the engine work properly.

 

[whodat526]

ok i see your point and can agree on that because the oil will be in the rings groves created during the honing process not the piston rings but in the cylinder its self but it cant be very much oil to change the level like others have stated thats what i was getting at because if thats the cause it would smoke and would be a weak motor

 

[Don87]

what i was saying is once it hot it will continue to be hot even if u just idle

but tell me why there is no smoke. because i know when i rebuild a engine and lightly coat the cylinder walls with oil it will smoke. the steel rings i believe or many to wear out after so long and so does the cylinder and then needs to be bored out or resleeved. i know i dont wont no oil getting past the rings on any motor i rebuild or i will have some mad customers because there will be some smoke and some blow by in the engine and will be low on compression because if oil and get by the rings so can air is all im saying

if im wrong please tell me i could be very well wrong but i believe im not and if i am i would have learned something new so dont think im being a smart*** i am just curious and dont mind being corrected i like to learn

There is always smoke, just because we can't see it with our weak eyes, doesn't mean it isn't there.
You've been around, you know that people have weak eyesight, weak hearing, and weak smell.
Just cause we can't see it doesn't mean it ain't there.

 

[Don87]

ok i see your point and can agree on that because the oil will be in the rings groves created during the honing process not the piston rings but in the cylinder its self but it cant be very much oil to change the level like others have stated thats what i was getting at because if thats the cause it would smoke and would be a weak motor

Yes sir, you are correct, it's not enough oil to cause a drop in the pan, but oil has to be there or the rings would heat up and sieze.

 

[whodat526]

and in some peoples case just cause they see it dont mean its there i have road in a truck with a mad like that now talk about scarry 8 hour ride

but it shouldn't use enough oil to drop the oil level unless u dont change it when u need to and let the oil break down and thin out

 

[whodat526]

Yes sir, you are correct, it's not enough oil to cause a drop in the pan, but oil has to be there or the rings would heat up and sieze.

and i have seen rings sieze to cylinder walls and break but figured that was because somebody over heated the engine which could be the case on some occastions. but u make all the sense in the world with that because everybody thinks the water is for cooling and oil is for lube but oil is also used for cooling down

 

[Don87]

and i have seen rings sieze to cylinder walls and break but figured that was because somebody over heated the engine which could be the case on some occastions. but u make all the sense in the world with that because everybody thinks the water is for cooling and oil is for lube but oil is also used for cooling down

Yes sir, and thank you.........oil is used for lubrication and cooling.
Most people don't understand the concept, but that is the case.
That is why they put 'oil coolers' on vehicles that are going to be doing a lot of towing or working in the fields.

 

[whodat526]

i just have one more dump question if a farmall cub does not have a water pump, but is water cooled. would that be a exception to the rule or not? because it does have a thermostat does it hurt the motor to just shut it down before idling down.

i am just curious how that motor cools the water is all i have never worked on one of the motors in a farmall and is curious to know

 

[whodat526]

maybe people that was saying it would drop the pan level will read the last few post, so they will understand the concept of the internals of a engine and how the work

 

[Transit]

Do not think that the temperature is a constant 3,000 deg. from the center to the cylinder wall. The cylinder walls will be cool enough to keep the oil from burning off if the engine is not over stressed. Once the oil is gone the piston rings will shatter.

 

[whodat526]

i understand that 100%

 

[Don87]

i just have one more dump question if a farmall cub does not have a water pump, but is water cooled. would that be a exception to the rule or not? because it does have a thermostat does it hurt the motor to just shut it down before idling down.

i am just curious how that motor cools the water is all i have never worked on one of the motors in a farmall and is curious to know

I personally have never worked on a cub, so I can't answer the question.
But I am looking to possibly buy one...........and after looking over the water circulation process, I'll be sure to post my findings here.

But since you told me about the 'no water pump'........I may have to rethink my ideas.

 

[johnrex62]

i just have one more dump question if a farmall cub does not have a water pump, but is water cooled. would that be a exception to the rule or not? because it does have a thermostat does it hurt the motor to just shut it down before idling down.

i am just curious how that motor cools the water is all i have never worked on one of the motors in a farmall and is curious to know

That is a great question! :anyone:

I would expect that convection circulation is in effect and the running state of the engine would be irrelevant other than to provide an oil bath to certain parts until they cooled sufficiently. I don't know if the engine temperatures get hot enough for this aspect of cooling or metalurgy to be critical though.