So I have always cooled down my mower engine for a few minutes on the lowest throttle setting I can, while i go and blow off the mower and driveway. Someone told me that letting it idle at such a low throttle is wrong and to let it idle at the standard throttle setting used for mowing. What's right??
Cooling down an air-cooled engine?!?!
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Depends on the engine, grab a pyrometer and test it out!
If it's a splash lube system, I believe low throttle is a bad idea. If you have pressurized oil, it's probably not as bad, although unnecessary.
The engine doesn't need much oil unloaded at idle anyways. Running it hard and then idling or shutting it down immediately is however going to lead to some degree of heat soak. I tend to run it wide open back to the shed(with the deck shut off), then idle it down when I get to the backyard area, back it in at idle and cut the ignition then.
Way i was taught by my friend who owned a landscaping company. He has Kohler engines and said that is what was recommended by the dealer. It did seem odd to me at first too.
The only time I think its necessary to let an engine idle before shutting it off is if its been used very hard in the minutes before. Unless you've been pushing the mower to the point of bogging, it hasn't been working that hard.
Engines like the chainsaw though, that have just been run WO in a big cut, I will let idle for a minute or two. If I've just been blipping through brush, then it gets shut off right away.
Engines like the chainsaw though, that have just been run WO in a big cut, I will let idle for a minute or two. If I've just been blipping through brush, then it gets shut off right away.
Ok, thanks!
I wish I could idle down my engine. For a while I eased off the deadman so it'd kill spark then coast down, "saving the brake". But that sucks fuel through the carb. Now I just walk a few seconds not actively mowing then jump off the handle abruptly.
I always let my engines down to an idle for a few seconds before shutting off. That way I don't suck fuel into the cylinder.
It wont cool down at idle, remember the fan also slows down with engine RPM.
If you could keep the fan RPM up and throttle it down that would be a different story but how much benefit if any it have is debatable.
Motor Cycle air cooled engines go many tens of thousand of miles and thousands of start/stop cycles with no damage and most don't even have a fan, the clearances are designed for this type of operation.
I think the best thing you can do for this type of small engine cooling is keeping the fan clear of debris.
If you could keep the fan RPM up and throttle it down that would be a different story but how much benefit if any it have is debatable.
Motor Cycle air cooled engines go many tens of thousand of miles and thousands of start/stop cycles with no damage and most don't even have a fan, the clearances are designed for this type of operation.
I think the best thing you can do for this type of small engine cooling is keeping the fan clear of debris.
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^^^Correct^^^
If a fuel shut off is available then use it. Shutting down an engine with a governor at WOT will dump lots of fuel on top of the piston thus diluting your oil. Keeping your carb dry when not in use will eliminate varnish deposits from the effects of ethanol.
Also a dirty air filter will cause a rich burn mixture and send carbon past the piston rings.
After I bought an infrared temp gauge I found the head near the spark plug of my air cooled ATV was 320F. I now use synthetic oil in my 4-cycle air cooled engines.
If a fuel shut off is available then use it. Shutting down an engine with a governor at WOT will dump lots of fuel on top of the piston thus diluting your oil. Keeping your carb dry when not in use will eliminate varnish deposits from the effects of ethanol.
Also a dirty air filter will cause a rich burn mixture and send carbon past the piston rings.
After I bought an infrared temp gauge I found the head near the spark plug of my air cooled ATV was 320F. I now use synthetic oil in my 4-cycle air cooled engines.
As Trav says,the fan does not move a lot of air at idle. So idling it you are actually heating it up. Just let it idle a few seconds then shut it down.
100% unnecessary to let an air cooled engine "cool down". Nothing happens to the very low stress internal parts when it's shut off after full load and full RPM. The parts simply shed heat slowly. The fuel ingested evaporates in seconds, you are kidding yourself to think otherwise.
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I don't think you can generalize that all air cooled engines are understressed though. 100+ hp/L isn't uncommon and many don't have cooling to allow a 100 % duty cycle, so at the end of a full throttle pull, just shutting it off will cook the oil due to residual heat on certain parts, like turbo coking.
The fuel you will injest during a high RPM shut down will wash oil off the piston rings.
No significant amount of fuel will be drawn in unless you were able to maintain engine RPM with the ignition turned off.
As soon as you push the throttle to the Stop position either manually or by a fan controlled blade the throttle plate returns to the closed position.
The idle passage will not allow enough fuel through to wash the cyl down but at the same time the oil slinger or pump is still throwing or pumping oil.
The small amount of fuel that is drawn in on a hot engine will be almost fully vaporised.
You cannot stop the engine in one revolution unless something broke.
There will be more cyl wash down starting a cold engine with closed choke, WOT and primer bulb depressed a few times. The fuel will not be vaporized very well cold.
As soon as you push the throttle to the Stop position either manually or by a fan controlled blade the throttle plate returns to the closed position.
The idle passage will not allow enough fuel through to wash the cyl down but at the same time the oil slinger or pump is still throwing or pumping oil.
The small amount of fuel that is drawn in on a hot engine will be almost fully vaporised.
You cannot stop the engine in one revolution unless something broke.
There will be more cyl wash down starting a cold engine with closed choke, WOT and primer bulb depressed a few times. The fuel will not be vaporized very well cold.
I was talking about an engine with a shut off switch and for this reason I disagree with you. Ed
Why would the cylinder be washed down with excess fuel? How?
Is the Hot engine burning raw fuel? If it is there is something wrong like it running way too rich.
Equate this in the most simple engine, a single cyl engine with no choke or adjustable throttle, just an on/off switch and a primer bulb.
These engines run at a fixed RPM that is load compensated by a fan controlled blade.
When you hit the kill switch the engine spins down quickly to a stop. Why are these engines not showing any unusual bore wear even on non sleeved etched aluminum bore engines?
Millions are in use use and no cylinder issues have been reported.
Try this..
Turn off the hot engine with the on/off switch and immediately pull the spark plug.
Is it wet or dry? I think you will find it is dry as a bone and light colored.
Do the same right after a cold start or one that needs to be cranked a lot, the plug may be soaking wet or at least damp with raw fuel and dark in color.
Believe it there is more cyl wash down on cold start than shutting down a warm engine regardless of RPM.
As always there are some exceptions but these are on older motor cycles and cars with carbs.
Electric valves were sometimes used for various things.
Is the Hot engine burning raw fuel? If it is there is something wrong like it running way too rich.
Equate this in the most simple engine, a single cyl engine with no choke or adjustable throttle, just an on/off switch and a primer bulb.
These engines run at a fixed RPM that is load compensated by a fan controlled blade.
When you hit the kill switch the engine spins down quickly to a stop. Why are these engines not showing any unusual bore wear even on non sleeved etched aluminum bore engines?
Millions are in use use and no cylinder issues have been reported.
Try this..
Turn off the hot engine with the on/off switch and immediately pull the spark plug.
Is it wet or dry? I think you will find it is dry as a bone and light colored.
Do the same right after a cold start or one that needs to be cranked a lot, the plug may be soaking wet or at least damp with raw fuel and dark in color.
Believe it there is more cyl wash down on cold start than shutting down a warm engine regardless of RPM.
As always there are some exceptions but these are on older motor cycles and cars with carbs.
Electric valves were sometimes used for various things.
I have never seen or heard of anyone do this with their lawnmower. Every time I see a lawnmower getting thrown out, it usually isn't the engine that failed.
This might make sense if lawnmowers had turbos.
This might make sense if lawnmowers had turbos.
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