Why idle before shut off?

[jake98]

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.

You should land with full/rich mixture, not lean, because if something wanders into your path you are ready for a go'round. You should lean out at altitude where the air is thin.

 

[johnrex62]

You read it almost right. I said the pump was to regulate, not restrict. You are correct in that the thermostat restricts; by closing when the water temp is too low. The pump regulates by forcing the flow of water to rapidly cool, and in the case of variable flow pumps, by adjusting the flow rate according to engine speed or electric motor speed regulation.

 

[whodat526]

i see now my bad i just misunderstood

 

[johnrex62]

No prob. I am not an engineer or mechanic, so if/when my understanding is erroneous I need you to call me on it so we both know. I will only put out what i think is true and makes sense to me, but we both know in a technical environment one unknown can change an entire philosophy. :thumbsup:

 

[Transit]

You should land with full/rich mixture, not lean, because if something wanders into your path you are ready for a go'round. You should lean out at altitude where the air is thin.

Just sitting here looking at the comments. Correct, the add fuel helps cool the engine too. Also enrich the fuel mixture 100 deg under max EGT temp produces Best Power. The extra fuel lowers the combustion temp but increases the mass of the gas in the cylinder hence increasing the Mean Effective Pressure = more hp.

 

[SPYDERLK]

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

There is so much to say here to bring things into perspective. A couple key issues:
-- o - how "free" of oil?
-- o - hot spots
Your mission Zman, should you choose to accept it.
larry

 

[whodat526]

There is so much to say here to bring things into perspective. A couple key issues:
-- o - how "free" of oil?
-- o - hot spots
Your mission Zman, should you choose to accept it.
larry

this as already been brought into perspective in previous post. i was talking about there was not enough oil in the cylinder walls to drop the oil level in the pan

 

[SPYDERLK]

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:

Yes -- the least of evils. Iv done it myself in those circumstances. There is little damage because the oil is replenished on the 1st stroke. What you dont want in a 4 stroke is real rich long term running.
larry

 

[The Haymaker]

Turbo charged engines need to run without a load for a few min. after having been run under heavy load to let the turbo cool.
Bill

"If" under a heavy load. Most of the time, just shut it down. Regular diesel? I just shut it down. Pretty rare I have a reason to shut of my big truck while doing 65 up a 12% with 80k on. The time it took to get it to wherever it is being shut down allowed plenty of time for the turbo and head to be cooled.

Now, stuck in a hole and boiling over a liquid cooled dirtbike and thinking it is a good idea to shut it down, that's a different story!

 

[SPYDERLK]

The oil does not go past the rings. Even if it does, each stroke of combustion burns it off instantly.

Its a matter of degree as to remanent oil film left by rings. And it may be hard to accept, but the combustion does not reach the cyl walls. They are "cold" and the mixture near them is poor due to being stagnant. In a truly cold engine the flamefront stops well short of the walls [a few thousandths "]. At operating temperature it gets closer, but the combustion cycle is so short the flame still cannot breach the proximal growingly stagnant area. The best way I know to see a demo is to wave your propane torch across a piece of hot oiled metal. It wont burn the oil unless you expose it to the torch much longer than a power stroke takes.
larry