Idle to cool down, isn't full throtno load better?

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Is this for an air-cooled engine? If so, more RPMs equal more heat. Unless this is not what you are asking?
 
I would suspect elevated rpms like 2k would probably help without introducing too much hear. I would think driving for a bit at low load would be better since you have airflow over the radiator
 
Yes this is for small air cooled 4 stroke engines. I would think the flywheel would move more air at a high rpm vs idling. You took away the load, so I don't think it would produce much heat.
 
Originally Posted By: motor_oil_madman
Yes this is for small air cooled 4 stroke engines. I would think the flywheel would move more air at a high rpm vs idling. You took away the load, so I don't think it would produce much heat.
While I agree that higher RPMs will move more air due to the flywheel spinning faster, I still do not think it is enough to overcome the amount of heat that will be generated. Even with zero load high RPMs are going to generate more heat-- right?
 
Easy to answer. Engine temperature goes up as RPM increases, regardless of load. A simple infrared thermometer illustrates this.
 
My experience on low speed, steep grade mountain roads is that you turn it off or downshift and keep going. I've had better luck pulling grades at 3500rpm vs 2000rpm in regards to over heating. None of my overheating was due to vehicle issues just large loads at low speed, 10-30mph. My lumberyard forklifts will over heat on 115° days. They will over heat at idle but will cool down if held at a mid range rpm for a few minutes. I guess I'm not a fan of the idle cool down.
 
Kohler 18 horsepower horizontal air cooled V twin. If I shut off after mowing without an idle cool down, it pops like a backfire. If it is idled for a few minutes then shut off while opening the throttle, no pop. I always let it cool at idle.
 
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The question is what are you trying to cool down? It's very common in development testing to run an engine at max load (max heat) followed by high idle to cool everything off quickly and give a thermal shock to the system.

If you have just been running low load then running higher rpm will probably raise the temps. But if you have been running high loads then running higher rpms will reduce temps quicker than just dropping to idle.
 
I had a Kohler twin do that - then I learned to shut the blades down and drive the 100' feet to park it at a mid speed - idle a minute or two ... shut down ...
 
Originally Posted By: RedOakRanch
My experience on low speed, steep grade mountain roads is that you turn it off or downshift and keep going. I've had better luck pulling grades at 3500rpm vs 2000rpm in regards to over heating. None of my overheating was due to vehicle issues just large loads at low speed, 10-30mph. My lumberyard forklifts will over heat on 115° days. They will over heat at idle but will cool down if held at a mid range rpm for a few minutes. I guess I'm not a fan of the idle cool down.


It's been awhile but aren't forklifts liquid cooled. If they will overheat idling they probably have a problems
 
Since we are talking about air cooled mowers (not mountain roads or forklifts), the fan is directly attached to the crankshaft, so if the engine is 1000 rpm, so is the fan.

On an air cooled car (VW), the fan is attached to a belt and pulley, so while the engine is at 1000 rpm, the fan is spinning much faster at 2000-3000 rpm. Thus moving a lot more air at idle than a direct drive lawn mower fan.

On an air cooled car, there should be sufficient fan spinning at idle to cool the engine. On a direct drive lawn mower, there likely isn't sufficient air movement at idle.

Idling a lawn mower engine is not the best for it. The fan and the splash oiling system is designed for 3100 rpm. Not 1000 rpm.

As to the OP's question, why do we care about cooling? Run the engine as designed, keep the cooling fins free of dirt/debris, and maintain it with new filters and an oil change every now and then and it will give you long life. Why do we need to care about its temperature? Its not likely to overheat unless we abuse it beyond its design limits.
 
The owner's manual for my riding mower specifically says to idle it for 15 seconds after mowing before shutting down, perhaps the OP has equipment that has a similar requirement. Yes, more air moves at high RPM, but high RPM burns more fuel and makes more heat. Idle uses the least fuel, and there is still a decent flow of air. Even at idle I can feel hot air blowing out of the cylinder shroud.
 
Idling before shutdown cools the engine. Less RPM equals less heat. If you shutdown from full, many times it will backfire or pop afterwards. This is because exhaust valve is hot enough (probably glowing) to burn the raw fuel. Idle down, valve cools, no pop or backfire.
 
Originally Posted By: RedOakRanch
My experience on low speed, steep grade mountain roads is that you turn it off or downshift and keep going. I've had better luck pulling grades at 3500rpm vs 2000rpm in regards to over heating. None of my overheating was due to vehicle issues just large loads at low speed, 10-30mph. My lumberyard forklifts will over heat on 115° days. They will over heat at idle but will cool down if held at a mid range rpm for a few minutes. I guess I'm not a fan of the idle cool down.


I think it depends on the intention.

If a guy were trying to get cooler oil through his turbo before shutting off the engine then your running at 3,500 RPM is not a good solution.
 
It depends on the set up.

I once had overheating problems with my Volvo 740 Turbo during a highway trip in very hot weather. [The radiator needed a good cleaning inside and out, but this episode took place in the middle of a 2 day trip.] When I tried to make a fuel stop after running at highway speed, the coolant temperature gauge went up quite alarmingly. Driving at high RPM in a low gear (at city speeds) would bring it down into the normal range again, but the gauge would show very hot again if I slowed down very much, or reduced the RPMs, or stopped at idle. It eventually cooled off enough, driving around at higher RPMs at city speeds, that I was able to fuel up and carry on with the trip. It was fine at highway speed even on mountain grades. The temperatures moderated as I got into the mountains and I had no further problems on the trip.

That Volvo had a belt driven fan (with a thermostatic control I believe) and a supplementary electric fan. And an oil cooled turbo that tended to glow faintly orange after driving at highway speed.

I think the problem was residual heat in the turbo, and an impaired radiator that required both forward speed and a fast turning fan to finally cool down.
 
I declutch the blades and reduce throttle to a fast idle while heading back to the garage. I then reduce to idle speed for 10 seconds or so and shut down. Ed
 
I never idle my air cooled lawn mowers. The engines run at full governed speed from start to shutdown. Fans doesn't move much air at idle.

I figure the cooldown on the rider is when I disengage the blades and drive it back into the garage. 15 mowing seasons and 700 hours so far with no issues.

Walk behind mower doesn't even have a throttle/engine speed control. Just release the bail to cut the spark and brake the flywheel from full speed.
 
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