quote:

Originally posted by kimber1911:

quote:

Originally posted by 12GA:
Interesting...the manual for my mower says to turn the key off at full throttle and I've never done otherwise.

Mine as well.

John Deere D160
Shutting Off Engine
1. Let engine run at high throttle without load for a few seconds.
2. Turn key to STOP position. Engine will stop and headlights will turn off.
3. Remove key.
4. Lock the park brake.

What reasoning do we have for these instructions?

The manual on my Deere indicates that on my air cooled engine full throttle is required to move enough air across the cooling fins to keep the engine cool.

Of course they don't explain why the throttle is adjustable to begin with.

Full throttle with no load will cool an engine down, due to the cooling fan moving air over the engine. At idle they can actually overheat due to lack of airflow. And most air cooled engines run ABOUT (give or take) 150 degrees more than ambient temp. Air cooled engines do not run at 350 to 400 degrees like a previous poster claims. Not even close. Add 150 degrees to your current outside temp, and that's ABOUT the temp of your air cooled small engine.

My Toro requires a full throttle shutdown, in fact, I seldom take it off full throttle. You can't hardly move and certainly can't mow with less than full throttle.

It is to avoid fouling the plugs or fuel pooling, All talk of heat and whatnot is BS. If you study thermodynamics you will see that the engine will never get as hot as it was while it was running. Take away the source of the heat and the heat will leave the object.

quote:

Originally posted by Rev. A. J. Forsyth:
It is to avoid fouling the plugs or fuel pooling, All talk of heat and whatnot is BS. If you study thermodynamics you will see that the engine will never get as hot as it was while it was running. Take away the source of the heat and the heat will leave the object.

This is untrue. With a water cooled engine, if you shut the engine off, it gets hotter because it normally has airflow and waterflow. After it's shutoff everything heat soaks and the heat rises 10-20F before it then starts cooling off. Like pulling a roast off of the smoker and putting it in a cooler, it too rises.

I was advised that idling a small engine that used a slinger type oiler was bad. At slow speed there is a chance of starving parts of oil. If it pressurized system I can see the reasoning behind it.

Echo 225 string trimmer instructions:

Stopping Engine: Release throttle trigger and allow engine to return to idle before shutting off engine.