The biggest Cub Cadet garden tractor?

[mgonitzke]

Cooling is directly proportional to engine RPM on an air-cooled engine. Mowing at partial throttle puts a higher load on the engine relative to the power it is capable of producing at that RPM (which, assuming you aren't creeping along at 0.1 mph, is probably nearly the same amount of power required to do the job as if you were operating at wide open throttle), but now with half to three fourths of the cooling capability. You are working the engine harder and hotter by running it at partial throttle under load. It is designed to be run under load at full throttle, and should be operated in this way.

 

[-CӞ]

i would think operating/fuel efficiency would peak at open throttle too, with the moving parts having ramped up their inertia and centrifugal happiness and such.
any credence to this undereducated hunch about running “in the groove?”

 

[Mark Miller]

I mow at full throttle also. However those engineers should have put a relay after all the safety idiot proof switches so we didn't have to do it ourselves in order to start the tractors every time...The brake pedal switch, seat occupancy switch and PTO are all ahead of the starter relay...I wonder about those engineers...Who was in charge of the paint??lol

 

[Bret McFarland]

i would think operating/fuel efficiency would peak at open throttle too, with the moving parts having ramped up their inertia and centrifugal happiness and such.
any credence to this undereducated hunch about running “in the groove?”

Actually there is an operating range for these engines from about 1800 to 3600 rpm (aka the powerband). At 2000 rpm, torque is peaking — above that you’re just spinning the mower blades faster.

 

[mgonitzke]

I mow at full throttle also. However those engineers should have put a relay after all the safety idiot proof switches so we didn't have to do it ourselves in order to start the tractors every time...The brake pedal switch, seat occupancy switch and PTO are all ahead of the starter relay...I wonder about those engineers...Who was in charge of the paint??lol

Don't blame the engineers for all the safety switches...blame the portion of society that can't operate a lawnmower without running over their pet/child/etc...

 

[Mark Miller]

Don't blame the engineers for all the safety switches...blame the portion of society that can't operate a lawnmower without running over their pet/child/etc...

Understood, they are necessary especially in todays or yesterday's era of litigation and stupidity, but to me it was clearly a lack of engineering enthusiasm of someone building/designing these SGT's which caused this problem which was a simple remedy of adding a "relay" and nothing less than a pita to figure out why the reason these SGT's would click 4 or 5 times before they started was the loss of juice at the starter relay because of all those safety switches. It was a trademark of them...I'm no engineer (by title) ,but I think someone in the line of development of these tractors could've seen a potential problem here and it was simple to fix..I noticed throughout the years MTD and others incorporated these components as a standard safety protocol and even I almost was in a bad scenario which could have sliced and diced me enlightening me on the importance of these standards. Still it was only a few dollar relay to solve this kind of thing...They are a pain but necessary as I realize..We as do it yourself people figure this stuff (problems) out, solving issues and we don't even design these tractors..Still I love them..Definitely no problem though as I have always been improving, disassembling, fabricating, modifying, restoring and improving everything I own as I just can't leave well enough alone...

 

[Bret McFarland]

Cooling is directly proportional to engine RPM on an air-cooled engine. Mowing at partial throttle puts a higher load on the engine relative to the power it is capable of producing at that RPM (which, assuming you aren't creeping along at 0.1 mph, is probably nearly the same amount of power required to do the job as if you were operating at wide open throttle), but now with half to three fourths of the cooling capability. You are working the engine harder and hotter by running it at partial throttle under load. It is designed to be run under load at full throttle, and should be operated in this way.

I believe that the manufacturers recommending WOT is to avoid complaints about the mower not cutting properly. Keeping the blades sharpened and adjusting the engine speed to the job, helps me take it easy my 40-year old Kohler and my grass looks great.

I doubt if you would find any operators manual that says the engine won't cool properly or be damaged if you run it at partial throttle. I don't agree with your theory. The motor will reach peak torque well before WOT. Like anyone else if I am mowing in high thick grass and I hear the engine bog I will adjust the engine speed or slow the tractor down (even at WOT). Do you go charging through tall grass wide open in the middle of July?

These engines have a wide operating range, not like a peaky motocross bike. This 1960's service bulletin from Kohler shows performance curves with peak torque happening at around 1800-2400 rpm. Also Interesting how it states ... "Recommended operating HP is 85% of maximum HP at speeds between 1800 and 3600 rpm. For continuous operation, at constant speed and load, limit output to 80% maximum HP." So in other words -- you don't have to run the H-LL out of the motor.

 

[dschwandt]

I believe that the manufacturers recommending WOT is to avoid complaints about the mower not cutting properly. Keeping the blades sharpened and adjusting the engine speed to the job, helps me take it easy my 40-year old Kohler and my grass looks great.

I doubt if you would find any operators manual that says the engine won't cool properly or be damaged if you run it at partial throttle. I don't agree with your theory. The motor will reach peak torque well before WOT. Like anyone else if I am mowing in high thick grass and I hear the engine bog I will adjust the engine speed or slow the tractor down (even at WOT). Do you go charging through tall grass wide open in the middle of July?

These engines have a wide operating range, not like a peaky motocross bike. This 1960's service bulletin from Kohler shows performance curves with peak torque happening at around 1800-2400 rpm. Also Interesting how it states ... "Recommended operating HP is 85% of maximum HP at speeds between 1800 and 3600 rpm. For continuous operation, at constant speed and load, limit output to 80% maximum HP." So in other words -- you don't have to run the H-LL out of the motor.

View attachment 153495

By the middle of July, i'm lucky to even have grass that is green, let alone tall and thick!!

 

[jdrong]

I believe that the manufacturers recommending WOT is to avoid complaints about the mower not cutting properly. Keeping the blades sharpened and adjusting the engine speed to the job, helps me take it easy my 40-year old Kohler and my grass looks great.

I doubt if you would find any operators manual that says the engine won't cool properly or be damaged if you run it at partial throttle. I don't agree with your theory. The motor will reach peak torque well before WOT. Like anyone else if I am mowing in high thick grass and I hear the engine bog I will adjust the engine speed or slow the tractor down (even at WOT). Do you go charging through tall grass wide open in the middle of July?

These engines have a wide operating range, not like a peaky motocross bike. This 1960's service bulletin from Kohler shows performance curves with peak torque happening at around 1800-2400 rpm. Also Interesting how it states ... "Recommended operating HP is 85% of maximum HP at speeds between 1800 and 3600 rpm. For continuous operation, at constant speed and load, limit output to 80% maximum HP." So in other words -- you don't have to run the H-LL out of the motor.

View attachment 153495

I agree with your post and have always adjusted the throttle according to my needs at the moment. usually about 3/4 throttle or less, depending on how much snow or grass. I have never run WOT continuously, there is after all a governor to help with that too. A WOT burns more gas creating more heat thus the need for more cooling. It makes since to me to run the engine within peak torque range. If you continuously need WOT then you are moving faster than your tractor and attachments can handle, get a tractor with more horse power or slow down.

 

[1811Cub]

This is another one of those "your results may vary". Some individuals get lucky and do not blow their hydro unit to pieces if they tow their tractors. Some people are fortunate for years to run their engines at part throttle while mowing, and not overheat their engines.

I tend to follow what the owners manual states, since they were written by people much more intelligent than I am.

 

[mgonitzke]

I agree with your post and have always adjusted the throttle according to my needs at the moment. usually about 3/4 throttle or less, depending on how much snow or grass. I have never run WOT continuously, there is after all a governor to help with that too. A WOT burns more gas creating more heat thus the need for more cooling. It makes since to me to run the engine within peak torque range. If you continuously need WOT then you are moving faster than your tractor and attachments can handle, get a tractor with more horse power or slow down.

The amount of fuel being burned depends on the load on the engine (and therefore how much power it is producing), not the throttle setting. With the throttle set wide open and no load, the governor will have the throttle butterfly nearly fully closed. When the load is increased, the butterfly valve will open further, allowing more air and fuel into the engine to allow it to produce the amount of power required by the load applied.

Let's say you are mowing grass and moving forward at 2 mph. This will require a certain amount of power to be produced, regardless of throttle setting, so the fuel burn will be about the same whether it is at 3/4 throttle or full throttle, and so the amount of heat that must be rejected is the same in both scenarios, but there is less cooling airflow at 3/4 throttle than full throttle.

 

[Doug Rusk]

Also the blade speed on these old cubs isn't nearly that of the zero turns everyone is so proud of. Not even at full throttle. I suppose if you mow your yard often enough so that the grass isn't that tall it works out for some of you. But early in the year here and with other chores needing done I'm not always able to mow as often as it needs it before getting a bit tall.

Yes the governor will add fuel when the load demands but it's second job is to keep engine under max operating rpms and from damaging itself by to many rpms. Or saying it a different way to keep it in safe operating range wot. Did cub set this rpm so we would burn more fuel and wear out our engines sooner?.well maybe but I would hope not and many are still running fine after lots of years at wide open throttle. I do vary my speed to match conditions and having used a snow blower the last few years and see on those particularly its easy to load them down before you know it if your not very diligent. Conditions change in a few feet going from not so much to a big drift.


I don't always run at wide open settings just moving around the drive or doing something light. But nearly always half or more and certainly wide open when mowing or blowing.

 

[1811Cub]

Always a good practice to run the engine for a minute throttled down prior to shutting off after a good workout. Also a good practice to engage AND disengage the PTO at about half throttle, then let 'er rip at full!

 

[Bret McFarland]

Pyle, if you mention Wide Open Throttle one more time ... 10 weeks KP!!!

 

[1811Cub]

I prefer SGT. Hulka

"Lighten up Francis!"

 

[Doug Rusk]

Pyle, if you mention Wide Open Throttle one more time ... 10 weeks KP!!!

View attachment 153537

 

[jdrong]

I will go with the previous Bret McFarland post from the Kohler engine manual. Pay special attention to the third paragraph, last sentence. I may be misunderstanding this part "For continuous operation, at constant speed and load, limit output to 80% maximum BHP". My understanding of this sentence is that to limit the maximum BHP to 80% I would have to limit the throttle to less than wide open. Also, there seems to be no mention of RPM versus cooling. Again, I may be misunderstanding this Kohler recommendation.

 

[mgonitzke]

I will go with the previous Bret McFarland post from the Kohler engine manual. Pay special attention to the third paragraph, last sentence. I may be misunderstanding this part "For continuous operation, at constant speed and load, limit output to 80% maximum BHP". My understanding of this sentence is that to limit the maximum BHP to 80% I would have to limit the throttle to less than wide open. Also, there seems to be no mention of RPM versus cooling. Again, I may be misunderstanding this Kohler recommendation.

As I stated before, the power output of the engine depends on the load placed on the engine, not on the throttle setting.

Somewhere in a pile of Kohler info I had a chart they made for the KT-17 series 2 showing the airflow of the flywheel fan vs RPM. If I can ever find that again I'll scan and post it.

To rephrase my previous point, 80% of rated power can be obtained at ~2600 rpm and above, but at 2600 rpm, cooling airflow is about 70% of what it would be at full throttle. So, under the same load, the engine is going to run hotter at a lower RPM.

This may not be an issue with a clean engine on a cool day, but a 100 degree day with some dirt and grass in the cooling fins could be another story.

 

[Bret McFarland]

As I stated before, the power output of the engine depends on the load placed on the engine, not on the throttle setting.

Somewhere in a pile of Kohler info I had a chart they made for the KT-17 series 2 showing the airflow of the flywheel fan vs RPM. If I can ever find that again I'll scan and post it.

To rephrase my previous point, 80% of rated power can be obtained at ~2600 rpm and above, but at 2600 rpm, cooling airflow is about 70% of what it would be at full throttle. So, under the same load, the engine is going to run hotter at a lower RPM.

This may not be an issue with a clean engine on a cool day, but a 100 degree day with some dirt and grass in the cooling fins could be another story.

According to the chart the load placed on engine can be handled efficiently when rpm reaches peak torque.

If your running in the sweet spot (~2200-3600) you're not overloading or generating excess heat. And and that point since rpm and cooling have a direct relationship -- lower rpm, less heat. More rpm, more heat. Also, again ... show me an operators manual that warns against operating at partial throttle.

 

[mgonitzke]

According to the chart the load placed on engine can be handled efficiently when rpm reaches peak torque.

If your running in the sweet spot (~2200-3600) you're not overloading or generating excess heat. And and that point since rpm and cooling have a direct relationship -- lower rpm, less heat. More rpm, more heat. Also, again ... show me an operators manual that warns against operating at partial throttle.

The chart shows the maximum power and torque that can be developed at a given RPM by the engine at sea level at 60°F. Nothing more.

The ACTUAL power output of the engine will depend on the load, from zero up to the maximum amount that can be produced at that RPM. Just setting the engine RPM does not determine the amount of power it produces. The load applied to the engine determines how much power is produced. So, I repeat myself again, for a load requiring X number of horsepower, roughly the same amount of fuel burned (and therefore heat generated) will occur whether you are operating the engine at WOT or some speed less than that at which it can still produce X horsepower. Since the amount of waste heat that must be rejected is essentially the same in either case, but the airflow is less at the lesser RPM, the engine will run hotter.

You probably won't find an operator's manual that warns against this, as this will not immediately destroy the engine in every circumstance (or even most circumstances), but once again, all else remaining constant, operating the engine under load at less than WOT will result in higher operating tempertures than if it is operated at WOT under the same load. Continued operation at higher temperatures can potentially shorten the life of the engine.