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#4481536 - 08/07/17 07:53 AM Idle to cool down, isn't full throtno load better?
motor_oil_madman Offline


Registered: 11/29/09
Posts: 4838
Loc: Houston, Texas
Wouldn't full throttle with no load be better at cooling than bringing it down to an idle?
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#4481540 - 08/07/17 07:56 AM Re: Idle to cool down, isn't full throtno load better? [Re: motor_oil_madman]
2015_PSD Offline


Registered: 09/26/10
Posts: 7231
Loc: SE Texas
Is this for an air-cooled engine? If so, more RPMs equal more heat. Unless this is not what you are asking?
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#4481547 - 08/07/17 08:09 AM Re: Idle to cool down, isn't full throtno load better? [Re: motor_oil_madman]
E150GT Offline


Registered: 03/11/12
Posts: 1090
Loc: San Antonio, TX
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
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#4481548 - 08/07/17 08:11 AM Re: Idle to cool down, isn't full throtno load better? [Re: motor_oil_madman]
motor_oil_madman Offline


Registered: 11/29/09
Posts: 4838
Loc: Houston, Texas
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.
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#4481558 - 08/07/17 08:20 AM Re: Idle to cool down, isn't full throtno load better? [Re: motor_oil_madman]
2015_PSD Offline


Registered: 09/26/10
Posts: 7231
Loc: SE Texas
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?
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#4481562 - 08/07/17 08:27 AM Re: Idle to cool down, isn't full throtno load better? [Re: motor_oil_madman]
Cujet Offline


Registered: 02/15/03
Posts: 7139
Loc: Jupiter, Florida
Easy to answer. Engine temperature goes up as RPM increases, regardless of load. A simple infrared thermometer illustrates this.
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#4481570 - 08/07/17 08:35 AM Re: Idle to cool down, isn't full throtno load better? [Re: motor_oil_madman]
RedOakRanch Offline


Registered: 11/10/13
Posts: 846
Loc: Central Coast California
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.
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#4481578 - 08/07/17 08:45 AM Re: Idle to cool down, isn't full throtno load better? [Re: RedOakRanch]
4WD Offline


Registered: 09/21/10
Posts: 6351
Loc: Texas
-


Edited by 4WD (08/07/17 08:47 AM)

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#4481594 - 08/07/17 09:14 AM Re: Idle to cool down, isn't full throtno load better? [Re: motor_oil_madman]
bugeye Offline


Registered: 04/10/15
Posts: 76
Loc: Pennsylvania
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.


Edited by bugeye (08/07/17 09:15 AM)

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#4481602 - 08/07/17 09:24 AM Re: Idle to cool down, isn't full throtno load better? [Re: motor_oil_madman]
09_GXP Offline


Registered: 12/14/10
Posts: 430
Loc: Indianapolis, IN
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.
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#4481610 - 08/07/17 09:31 AM Re: Idle to cool down, isn't full throtno load better? [Re: bugeye]
4WD Offline


Registered: 09/21/10
Posts: 6351
Loc: Texas
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 ...

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#4481619 - 08/07/17 09:41 AM Re: Idle to cool down, isn't full throtno load better? [Re: RedOakRanch]
John_VT Offline


Registered: 07/08/17
Posts: 43
Loc: Vermont
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
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#4481631 - 08/07/17 09:55 AM Re: Idle to cool down, isn't full throtno load better? [Re: motor_oil_madman]
bubbatime Offline


Registered: 03/18/08
Posts: 5615
Loc: South Florida
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.
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#4481729 - 08/07/17 11:36 AM Re: Idle to cool down, isn't full throtno load better? [Re: bubbatime]
Dave Sherman Offline


Registered: 01/03/06
Posts: 1071
Loc: Ohio
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.
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#4481835 - 08/07/17 01:47 PM Re: Idle to cool down, isn't full throtno load better? [Re: motor_oil_madman]
Propflux01 Offline


Registered: 09/26/02
Posts: 3398
Loc: Arkansastan
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.
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