Run full Throttle? - Snowblower Forum : Snow Blower Forums
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post #1 of 42 Old 12-12-2015, 09:09 AM Thread Starter
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Run full Throttle?

Hey guys.... My uncle who is the family mechanical guru, well deserved I might add, told me that it's necessary to run small air cooled engines at full throttle all the time or otherwise they might overheat. The thinking being that at lower speeds there is insufficient airflow over the cooling fins to keep things cool. Not sure I go along with that, what are your thoughts on it?
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post #2 of 42 Old 12-12-2015, 09:26 AM
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Listen to your Uncle. Why are there so many small, air cooled engine w/o throttle controls? You start them up, give them a few seconds then open them up.

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post #3 of 42 Old 12-12-2015, 09:30 AM
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Logical operation of the implements usually takes over. Mowers, blowers and such simply need RPM to perform so it's usually idle or all.

I have never heard that position on engine cooling but I have to believe that there is some truth to it. It probably comes down to shades of gray including HP, RPM, load (governor pull) and even block & fin cleanliness.

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post #4 of 42 Old 12-12-2015, 09:40 AM
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I don't buy it!

Most engines that have no throttle (ie run full speed all the time) have other variants that do have throttles. If running them at slow speed could cause damage, they would never have a throttle.

In one way your uncle's argument does have a sensible basis in physics. With most blowers like the ones that cool small engines, airflow doesn't increase linearly with speed... it increases exponentially. So yes at higher speed there's more cooling.

But "the rest of the story" is this: at low speed, the engine is generally under very little load. Idling at 1200 RPM or so, the engine is only producing a tiny fraction of the amount of heat it produces at 3600 RPM and full load.

Now putting a heavy load on an engine at low RPM could tip that balance... I definitely would not advocate running your snowblower through a foot of heavy snow with the engine spinning at 1500 RPM. But the usual mode of operation where the engine is idled when not actively being used, and at high RPM when under load, should be fine.

I also happen to be of the opinion that starting an engine at full throtle is very unkind to it. Expecting it to produce a lot of power, even momentarily to come up to governed RPM, before the oil has a chance to circulate has to be tough on an engine. Whenever possible, I usually start engines with the throttle about 1/4 open so the governor can help keep it running but it stays at low RPM until the oil has had a chance to get everywhere it needs to be.

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post #5 of 42 Old 12-12-2015, 10:11 AM
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the fins for air cooled engines, either large or small, are to create a larger surface area to keep the engine cooler. ( the same principle with computer cpu's and memory) the movement of the equipment (or fan ) will help air move through the fins to aid in cooling. nothing to do with engine speed. the use of an air filter on small engines does help it run cooler and use less fuel, and are used on small engines mainly for warmer weather. most snowblower engines do not have an air cleaner to prevent water and ice build up in the carb, unless their is a heater of some type to prevent icing, such as on the older ariens where the engines were used for summer attachments. but the lack of an air cleaner makes these engines run hot and will be damaged if used in warm weather. however your uncle is correct also. when in "use" and at full throttle the equipment is in motion therefore more air movement across the fins (larger surface area ), keeping the engine cooler. when sitting and at idle the equipment is mostly not being used (in motion) therefore less air passing over the fins allowing the engine to run hotter than when at full throttle and in motion. it is very important to make sure the fins are clean and not clogged with debris. so bottom line it is not the engine speed, but the movement of air through the fins. and it cuts cost to the maker having no throttle. hope that make sense
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post #6 of 42 Old 12-12-2015, 10:30 AM
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Another aspect of full throttle running is on lawn tractors, particularly with hydro trans. Most are now set up to run by belt. The input pulley of the trans has a fan also that runs to cool the trans. The belt that drives the fan comes from the engine PTO, if you run low idle the perception is your "babying" the unit. In reality, operator weight and unit weight still has to be overcome by the engine and trans. Hot trans equals short life. The hood area on tractors is designed to funnel air over the engine at full throttle also.
On liquid cooled engines, it works against you a bit in the winter use. In the summer running at half throttle and idle is working against the design.
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post #7 of 42 Old 12-12-2015, 11:07 AM
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If running at a mid speed would cause a problem it should show up more on summer use equipment. Seeing we're using blowers in 50-80 degree cooler weather we have a huge advantage in cooling to begin with.

Not to say there isn't something to the idea but I've never run into a problem with my rider and when I 'm using it for moving stuff, dirt, brush, plants, ... I usually run at mid throttle to be easier on the engine and less noise for the neighbors, no problems noted yet.

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post #8 of 42 Old 12-12-2015, 11:20 AM
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K4frog, It's a debate that will never end. 25% of mytractor forum seems to be dedicated to arguments over the best way to run an engine. Full throttle wears the internals vs low throttle overheats the externals. I stay in the camp that a properly lubricated engine is designed to run at full throttle and a working hydro needs to be clear of debris and have a nice fan blowing on it. An overheated hydro can make a pristine tractor a parts machine, IMO.
Snowblowers and the temps we run in, likely not an issue, agreed.

Last edited by jtclays; 12-12-2015 at 12:12 PM.
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post #9 of 42 Old 12-12-2015, 11:32 AM
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Quote:
Originally Posted by jtclays View Post
K$frog, It's a debate that will never end. 25% of mytractor forum seems to be dedicated to arguments over the best way to run an engine. Full throttle wears the internals vs low throttle overheats the externals. I stay in the camp that a properly lubricated engine is designed to run at full throttle and a working hydro needs to be clear of debris and have a nice fan blowing on it. An overheated hydro can make a pristine tractor a parts machine, IMO.
Snowblowers and the temps we run in, likely not an issue, agreed.
^^ ^^ ^^
What jt said.

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post #10 of 42 Old 12-12-2015, 12:02 PM
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I have always heard that as well. I say go for full throttle. The other thing to remember is most small engines are splash lubricated so the faster you run them the more the oil splashes around.

Please direct all snow blower questions to the forums and not to me with PMs.
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