I have never seen any special cool down requirements for air-cooled engines in the manuals of the mowers I have used.

 

I have a Toro z560 and the manual states set throttle to half and let idle for 60 seconds. What your doing is probably good as long as it's at least a minute. I always do that and then let it idle while I put up the gate and get the trimmer started.

 

Full throttle no load is best for cool down. The slower the engine runs means less air flow over fcooling fins. Slowing engine down for cool down is a myth on air cooled, it builds heat.

 

It may be a myth but it works for me. Every time I shut an engine down at full throttle bad things happen. Big back fires, smoke at re-start. Stuff like that. I let mine idle for a minute or so if I can.

 

Full throttle no load is best for cool down. The slower the engine runs means less air flow over fcooling fins. Slowing engine down for cool down is a myth on air cooled, it builds heat.

You are absolutely correct, the principle of more air movement means cooler a engine.

The same principal applies to a liquid cooled engine as well, the more air movement through the radiator the cooler the engine runs. When you have enough mechanical air movement (by fan) over the radiator the lower the engine temperature. When you are sitting at a stop light if you do not have enough air circulating through the radiator you can watch the temperature gage rise, once you are moving at 60 mph again the engine temperature will drop.

They build vehicles with just enough radiator surface to keep the engine at the designed operating temperature. When and if the radiator gets a certain amount of debris covering it and cuts the cooling surface by a very small percentage the engine will start gaining heat from low air flow.

This scenario states why an air cooled engine cools best with the cooling fans at maximum rpm's, it is just a common sense thing.

When you let a turbo charged diesel engine idle to cool down temperature, you are not just letting the engine cool but you are cooling the turbo charger also. The diesel applications use a larger radiator with more flues to give extra room for surface restriction because they are normally running in a dirtier environment.

When the engine is taken from under blade rotation load it is cooling itself to the best of it's ability with the mower stationary at full throttle.

 

It may be a myth but it works for me. Every time I shut an engine down at full throttle bad things happen. Big back fires, smoke at re-start. Stuff like that. I let mine idle for a minute or so if I can.

That is why newer engines are designed with fuel shut off solenoids. Once you kill the engine at full throttle, it instantly stops fuel from entering the cylinders. The momentum of the engine coasting to a stop purges all extra fuel out of the system/muffler so there is nothing left to ignite(backfire).

 

It may be a myth but it works for me. Every time I shut an engine down at full throttle bad things happen. Big back fires, smoke at re-start. Stuff like that. I let mine idle for a minute or so if I can.

Did you and Bruce get together, he said he left you a message on your phone.

 

Did you and Bruce get together, he said he left you a message on your phone.

I'm calling him tomorrow afternoon.

 

That is why newer engines are designed with fuel shut off solenoids. Once you kill the engine at full throttle, it instantly stops fuel from entering the cylinders. The momentum of the engine coasting to a stop purges all extra fuel out of the system/muffler so there is nothing left to ignite(backfire).

That only works on engines that have those solenoids. Neither of my bigger Kaws (two 15s) that are only 2 years old have them. My EFI Kohler doesn't need one but it will smoke pretty badly on restart if I don't let it idle for a minute.

Let me put it this way....

Nothing bad has ever happened because I did let them idle.

 

my 15hp toro wb says 1-3 min at idle... ITS NOT ABOUT COOLING, its about making sure there is not a ton of unburnt fuel left over. shutting down from full throttle can leave excess fuel in and can damage valves ect.

 

Full throttle no load is best for cool down. The slower the engine runs means less air flow over fcooling fins. Slowing engine down for cool down is a myth on air cooled, it builds heat.

Have you considered that an engine at idle generates less heat and doesn't require as much cooling? If an idling engine doesn't cool well then why do engines have a fast idle setting for warming up? If full throttle no load was the best for cool down then why don't any manufacuters recommend it?

Scott

 

Have you considered that an engine at idle generates less heat and doesn't require as much cooling? If an idling engine doesn't cool well then why do engines have a fast idle setting for warming up? If full throttle no load was the best for cool down then why don't any manufacuters recommend it?

Scott

Exacty. If you grab the muffler after shut down under both situations you will find it cools down better at low to part throttle rather than full. Cool down time is about stabilizing temperatures throughout the engine prior to shutdown.

 

hello after run time on any engine is about

stabalizing temp thru out the engine to the lowest level and evenly as a result .
Running an engine at max or high throttle unloaded is never a good idea .
Running an engine such as eg kohler 25 hp 1-5mins at 1200 rpm to 1800rpm for cool down is the best way . This promotes good air flow with little induced load/heat as when u r when the engine is at max rpm

NO INDUSTRIAL ENGINE IS COOLED AT MAX THROTTLE

TOMO

 

Running an engine at max or high throttle unloaded is never a good idea .

NO INDUSTRIAL ENGINE IS COOLED AT MAX THROTTLE

I'm not changing my mind or practices here but I wanted to point something out.

We don't run these engines at full throttle except for a severe load where the governor may push the throttle all of the way. Full throttle at no load would result in about 6000 RPM. When you push the lever to wind the engine up it goes until it hits a mechanical "stop" or set screw.

This whole shutting at engine down at "full throttle" is kind of bizarre anyway.

How many of you run your car to 3600 RPM before you shut it off? No one. If not then why do you feel a compulsion to do it to your mower engine?

Or.... From a longevity standpoint.... Does it really matter?

 

Im not saying anything bad will happen. The question was what was the proper way to cool an air cooled engine. If you experience bad things then don't do it. I would say it would be best to cool at full throttle then let idle for a short time before you kill it. JMO

 

hello after run time on any engine is about

stabalizing temp thru out the engine to the lowest level and evenly as a result .
Running an engine at max or high throttle unloaded is never a good idea .
Running an engine such as eg kohler 25 hp 1-5mins at 1200 rpm to 1800rpm for cool down is the best way . This promotes good air flow with little induced load/heat as when u r when the engine is at max rpm

NO INDUSTRIAL ENGINE IS COOLED AT MAX THROTTLE

TOMO

This is directly from a Kohler engineer that actually does temperature testing on these engines. He has a 28 efi mounted in a lawn and garden tractor for testing purposes, he said once you turn the blades off the engine cools down very quickly to a temperature sufficient to shut the engine down.

He said "people that are in the commercial mowing business by the time they turn off their blades and drive to a trailer and load their machine the engine has cooled well enough to be switched off." He also stated that if you let it sit there and run at idle speed the temperature will slowly drop more over a period of time but it would not increase the longevity of the engine.

He said most people pull them to where they are going to be parked pulled back the throttle and switch them off and there are no guide lines really to follow.

 

This is directly from a Kohler engineer that actually does temperature testing on these engines. He has a 28 efi mounted in a lawn and garden tractor for testing purposes, he said once you turn the blades off the engine cools down very quickly to a temperature sufficient to shut the engine down.

He said "people that are in the commercial mowing business by the time they turn off their blades and drive to a trailer and load their machine the engine has cooled well enough to be switched off." He also stated that if you let it sit there and run at idle speed the temperature will slowly drop more over a period of time but it would not increase the longevity of the engine.

He said most people pull them to where they are going to be parked pulled back the throttle and switch them off and there are no guide lines really to follow.

If any of the four Kohler 27's we run are shut down that way they will run on. They need to cool at a lower engine speed.

Scott

 

The manual for my Kohler 30 says to shut down at between half and full throttle, the same as my dealer instructed when I bought the machine.

 

Internal Combustion Engines work on the principle of a series of controlled explosions (combustion) inside a chamber (internal). Each explosion generates pressure and heat (power).

Low RPMs = lower number of explosions = lower temperatures
High RPMs = higher number of explosions = higher temperatures

During use at high rpms, engine components inside and outside operate at different temperatures due to cooling systems and airflow. Cooling down at idle or low rpms allows all components to thermo-stabilize so there is less stress on all systems.

An extreme example would be hitting a hot engine with cold water from a hose, you may get away with it a couple of times but, eventually something will give.

 

My crews operate in hot climates for eight months out of the year, just like the other southern LCO's.
I, personally, shut off the motor at between 1/2 and 3/4 throttle as that is the setting when the blades are first engaged then disengaged.
I have noticed that when the engines are idled down then shut off they start much more reluctantly than at the slightly higher settings.
I spoke with both Kohler and Kawasaki about this and both said essentially the same thing. At the higher ambient temps common to my a.o. the fuel tends to volitalize more quickly resulting in a leaner start condition at idle which in turn makes the hot motor more difficult to start.

 

If any of the four Kohler 27's we run are shut down that way they will run on. They need to cool at a lower engine speed.

Scott

The 27 hp Kohler's I owned would not switch off period without backfiring if the throttle was not 3/4 to wide open and Kohler is the one that told me to use that procedure, it worked perfectly.

The 28 efi I run now cranks, runs and switches off perfectly in any and all throttle positions.

 

Its funny how different people with the same equipment can have such different experiences. Maybe because ours get the bare minimum maintenance as far as the cooling system goes and they are turning 72" decks.

Scott

 

Its funny how different people with the same equipment can have such different experiences. Maybe because ours get the bare minimum maintenance as far as the cooling system goes and they are turning 72" decks.

Scott

Yep, they can come off the assembly line back to back and be different machines, it is kinda amazing. We are talking about American assembly lines here, seems like the Japanese have better quality control.

I can't believe I had to say that but it is the exact reason Toyota has taken over number one in the automobile industry, they listen to and care about their customers.

I have been running John Deere diesel and gas engines with a few Allis Chalmers and International's thrown in the mix for over 40 years and no matter what anybody says you will always have more maintenance with liquid cooled than air cooled engines. There is just nothing to maintain about air cooled engines, I have seen many water pump failures, belts broken, hose's break, cleaned, flushed and put new coolant with additives in many radiators. I have also taken out many radiators to have them roded and repaired and replaced several with new ones in my lifetime.

The experiences I am talking about are in machinery with farming applications but not once have I done anything for a cooling problem with an air cooled gas engine in a mowing application. I do blow off the engine and entire mower to clean it occasionally whether I think it needs it or not but this is no special maintenance for cooling capability alone, I just don't care about any equipment being filthy.

Liquid cooled has it's place but as far as commercial mowing that is entirely up to the individual and I personally am not going to have my mower put in the casket with me so if it blows up tomorrow I will buy a new one.

I know commercial cutters with 2000 to over 4000 hrs. on Kohler air cooled engines with nothing but oil and and air filter changes. I doubt seriously there is many if any liquid cooled engines that have done this with 0 maintenance to the cooling system.

What say this, liquid cooled engine fans!

 

Its funny how different people with the same equipment can have such different experiences. Maybe because ours get the bare minimum maintenance as far as the cooling system goes and they are turning 72" decks.

Scott

Partner, I think you and I got these comments in the wrong thread, it is kinda funny what happens early in the morning. I saw your post and though I was in the liquid versus air cooled thread.:hammerhead:

 

hello ,
in regards to your reference about cool down on eg 28hp kohler .You will discover in warm to hot climate the engine oil will be very hot and most likely excessively so . I have a oil temp guages on the kohler sumps. Once the machine has returned from the job and then sitting on the trailer it still takes a few minutes 4 the oil temp to drop to AN ACCEPTABLE LEVEL .Oil coolers 11x 8 inch with electric fans r fitted to all my kohlers.

Measuring of the oil temp in an aircooled engine is very very impotant .

The oil cooler system was designed with partial assistance from the technical dept. at kohler .

tomo :waving: