Can running at 65% or less hurt your engine?

Steve Job

Steve Job

Pre-takeoff checklist
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Steve Job
So I attended a Wings seminar last weekend, and the presenter emphatically stated that running your engine at anything less than 75% (preferably 85%) and 50 degrees ROP will hurt your engine - as long as you don't go over 400 degrees CHT. This is contrary to everything I've read regarding the "red zone" (except for the CHT limit). The logic used was that you are "lugging" the engine if you're running at a lower power setting. I asked if this applied to the simple O-320 (non-CS) in our Warrior. We're usually not in a big hurry, and run it at 2300 RPM, leaned to just rich of running rough. His answer was "yes". I'm having a hard time wrapping my brain around the fact that low power settings are bad. Are we really hurting our engine?
 
Steve Job said:
So I attended a Wings seminar last weekend, and the presenter emphatically stated that running your engine at anything less than 75% (preferably 85%) and 50 degrees ROP will hurt your engine
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That's the exact opposite of everything I have heard from every source on engine operations, and of all my understanding of engine operations.
 
Steve Job said:
So I attended a Wings seminar last weekend, and the presenter emphatically stated that running your engine at anything less than 75% (preferably 85%) and 50 degrees ROP will hurt your engine - as long as you don't go over 400 degrees CHT. This is contrary to everything I've read regarding the "red zone" (except for the CHT limit). The logic used was that you are "lugging" the engine if you're running at a lower power setting. I asked if this applied to the simple O-320 (non-CS) in our Warrior. We're usually not in a big hurry, and run it at 2300 RPM, leaned to just rich of running rough. His answer was "yes". I'm having a hard time wrapping my brain around the fact that low power settings are bad. Are we really hurting our engine?
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NO..... Fixed pitch prop on a non turbo'ed motor will NOT suffer from "lugging"..:no::nonod:
 
Presenter had impressive credentials. Engineering degree (worked in engine development for Mercury Marine for some years), retired, then got his A&P. He related a number of anecdotes regarding Corvairs and VW engines that last much longer when run "hard". His specific recommendation was to always have the throttle all the way to the firewall for CS folks, and for us non-CS folks, back off the throttle to keep the tach at the top of the green (after leaning for max RPM). Spend your money on gas, not maintenance!
We're not in a hurry to replace our engine. Can we extend our engine life by running it at lower power settings?
 
That guy is wrong. You might ignore his degrees and instead accept advice from a collective of airplane owners/mechanics on here.

2300 RPM and leaned the way you describe is the correct way to extract max engine life and fuel economy from your warrior.


What he says does have some merit. Consider this FT climbs and then cruising at 50-65% power all the time would be considered "running it hard" for a car or motorcycle engine.
 
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I hadn't thought about what running a car/motorcycle at 50-65% power all the time would look like, but you're right; it would seem unusually hard compared to normal driving.
Thanks to everyone for confirming my own thoughts on this matter.
 
Steve Job said:
Presenter had impressive credentials. Engineering degree (worked in engine development for Mercury Marine for some years), retired, then got his A&P. He related a number of anecdotes regarding Corvairs and VW engines that last much longer when run "hard". His specific recommendation was to always have the throttle all the way to the firewall for CS folks, and for us non-CS folks, back off the throttle to keep the tach at the top of the green (after leaning for max RPM). Spend your money on gas, not maintenance!
We're not in a hurry to replace our engine. Can we extend our engine life by running it at lower power settings?
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I nearly always fly in cruise with the throttles to the firewall as you say, and that is nearly always less than 65% power. IOW not only is your friend wrong, he's clueless. And having had a little interaction with engineers at mercury marine when i worked in engine development at GM, I'd say he was in good company there.
 
Steve Job said:
So I attended a Wings seminar last weekend, and the presenter emphatically stated that running your engine at anything less than 75% (preferably 85%) and 50 degrees ROP will hurt your engine - as long as you don't go over 400 degrees CHT. This is contrary to everything I've read regarding the "red zone" (except for the CHT limit). The logic used was that you are "lugging" the engine if you're running at a lower power setting. I asked if this applied to the simple O-320 (non-CS) in our Warrior. We're usually not in a big hurry, and run it at 2300 RPM, leaned to just rich of running rough. His answer was "yes". I'm having a hard time wrapping my brain around the fact that low power settings are bad. Are we really hurting our engine?
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First of all the issue of "lugging" refers to high MP and relatively low RPM. This can result in main and con rod bearing distress due to the associated low oil pressure/flow combined with high piston forces. It also typically causes excessive vibration because the mechanisms to absorb vibration lose effectiveness at low RPM. Running 2300 RPM and 65% power doesn't generate any of those issues.

Second, it's been well documented/demonstrated that operation at or below 65% generally cannot create damaging pressures in the cylinders. And there's nothing magic about 65%, it's just that if the engine is robust enough to run at full power with a rich (slow burning) mixture the peak pressure at 65% power will be less regardless of the mixture or MAP.

I suspect that your presenter has taken a few accepted facts about engine operation and added his own "common sense" (i.e. unproven hypotheses with no real basis) and come up with total BS because he doesn't actually understand the underlying issues affecting engine performance and longevity.

It's also been shown that running 80+% power with a 50 ROP mixture is about as damaging and abusive as you can achieve without a turbocharger.

Finally if there was any truth to this nonsense it would mean you should never fly above 6000 DA with a NA engine because you can't get 75% power there.
 
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Most of my flying, it's impossible to get up to 75%! When ground is 5500 msl, I'm lucky to be flying at 65%!
 
Steve Job said:
We're not in a hurry to replace our engine. Can we extend our engine life by running it at lower power settings?
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Yes, and outside of post-overhaul/new cylinder break-in. running at 65% rather than 75% with a horizontally opposed piston aircraft engine will accomplish what you want. Unless he was talking about that break-in period, the person who told you otherwise is talking out of his hat.
 
Steve Job said:
So I attended a Wings seminar last weekend, and the presenter emphatically stated that running your engine at anything less than 75% (preferably 85%) and 50 degrees ROP will hurt your engine - as long as you don't go over 400 degrees CHT. ...snip...
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I don't get this. You are saying that less than 75% and 50 ROP will hurt your engine if CHT stays under 400 deg???? But, it won't if it goes over 400 deg????

It would seem that the two statements may coincide correctly if you change one word and that would be "more" than 75% ...

Are you certain that this is not what you intended to say?



If you stand by the original statement, then I should be needing a new engine soon because I tend to operate near 50% at 2100 rpm if I am going somewhere not in a hurry or even as low as 40% if just putting around. :dunno:
 
He is wrong. In fact, he is very wrong.

Signed,
An engineer with more relevant and impressive credentials
 
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Steve Job said:
Presenter had impressive credentials. Engineering degree (worked in engine development for Mercury Marine for some years), retired, then got his A&P.
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All "credentials" mean is that somehow you managed to not flunk out of school and somehow managed to not get fired. Did he retire on his own, or did management finally get fed up and push him out the door?
 
Capt. Geoffrey Thorpe said:
All "credentials" mean is that somehow you managed to not flunk out of school and somehow managed to not get fired. Did he retire on his own, or did management finally get fed up and push him out the door?
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Agreed. Even then, there were a lot of engineers at my last job who didn't know a damn thing about engines. I remember being told by one that diesels didn't work well in planes because they had a higher RPM and needed a gearbox. Sigh..
 
Steve Job said:
Presenter had impressive credentials. Engineering degree (worked in engine development for Mercury Marine for some years), retired, then got his A&P....?
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My question to all the A&P's out there...

When you are studying and testing for the Powerplant rating, do you actually have to demonstrate your basic knowledge of internal combustion engines or can you just BS your way through the whole process....:dunno::dunno:.. Is there not questions on the test to confirm this?:dunno:

Personally, when I see the term ( A&P) after a persons signature I assume they are somewhat intelligent in the concept of motors... Maybe I have been wrong all these years in assuming this..:redface:
 
Ted DuPuis said:
Agreed. Even then, there were a lot of engineers at my last job who didn't know a damn thing about engines. I remember being told by one that diesels didn't work well in planes because they had a higher RPM and needed a gearbox. Sigh..
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Having worked on diesels (non aviation) I would think the rpm's would be perfect for aircraft.
 
tmyers said:
Having worked on diesels (non aviation) I would think the rpm's would be perfect for aircraft.
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Yep. What this person was illustrating was a lack of basic engine knowledge, and was looking at the Thielert engines. They do require a gearbox because of their higher RPM design, but that is not at all representative of typical diesles. A pair of Cummins turbo diesels out of a Ram would be great direct drive, just very heavy.
 
Some times I wonder why the manufacturers spent all the time and money developing the power setting charts and placed them in the POH/OM.
 
Steve Job said:
Presenter had impressive credentials. Engineering degree (worked in engine development for Mercury Marine for some years)
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Having an extensive background in marine engineering does not equal impressive credentials when talking about airplane engines. Very different applications.....and I say that as someone with sone background in marine engineering.

His comment that you should ideally run your engine at 85% power is very telling of a lack of aviation understanding. How many folks with NA engines can even get that much power unless they are running down low on the deck?
 
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Fearless Tower said:
Having an extensive background in marine engineering does not equal impressive credentials when talking about airplane engines. Very different applications.....and I say that as someone with sone background in marine engineering.
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I respectfully disagree...

1- Both applications have engines creating movement through a fluid..

2- Both have engines operating at high power levels...

3- Both convert motion through propellers....

4- Both have engines that run at a sustained power settings....

Other then that.. not too many similaraties..:D
 
Ted DuPuis said:
He is wrong. In fact, he is very wrong.

Signed,
An engineer with more relevant and impressive credentials
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:yeahthat:

And even without an engineering background, it defies logic. When does less stress on something cause it to fail sooner? :dunno:

An old Mooney guru believed an engine had a fixed number of RPMs in it. The faster you burned through those, the sooner you'd overhaul. He recognized there were other factors involved, but there's some basic common sense to the underlying premise. Every revolution involves the imposition of some form of stress and some ultra-small amount of wear.
 
I agree with the forum consensus about running powers.

I think there may be some cultural differences between flying and boat cruising.

When I took a Coast Guard class working on my captains license the Maintenance head guru in Boston said almost the same thing. But he said that an outboard engine hardly ever lasted more than 3 years due to electrolysis and corrosion conditions being in the water and not being able to completely mitigate those issues. So you get your best longevity going full speed ahead.

I am paraphrasing and do not remember exactly what he said so to be fair I might have completely misunderstood but I remember something about best costs being "don't dally, just get there fast."

With boats, it seems to make sense. Even within aviation there is the argument of do you fly 120 knots or 100 knots and what are the relative hourly costs in doing either. Especially if you figure the time based maintenance: 500 hr new mags and other parts, 1000 hr other parts and 2000 hr engine tbo. The slower you fly the more cost per mile as maintenance is higher than saved fuel.

But I do not believe in TBO but rather conditioned based maintenance and their some TLC might help.

Higher pressures surely cause greater wear. You have higher cylinder head pressures with higher heat, actually the other way around, that is why we measure heat as we do not have an easy way to measure CHPs.

So are their other forces fatiguing metals besides pressures? Harmonic vibration? I do not know but I can tell you that running a Turbo hard is an expensive proposition.
 
Tom-D said:
Some times I wonder why the manufacturers spent all the time and money developing the power setting charts and placed them in the POH/OM.
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Because they met the numbers that marketing and airframers wanted.
 
Take a look at my Forum name...I know something about VW engines and you say this guy has experience with them. Perhaps that clouded his perception. VW engines are particularly vulnerable to lugging and must be kept at a moderate to high RPM's to ensure long life. And even when you do that...they don't last as long as today's engines, because the high rpm's cause rapid wear. Expect 75K if you're luck on an old VW engine.

Based on my experience, climb is good at 100%, and the lower the better after that. Be nice to your engine!
 
Ted DuPuis said:
Yep. What this person was illustrating was a lack of basic engine knowledge, and was looking at the Thielert engines. They do require a gearbox because of their higher RPM design, but that is not at all representative of typical diesles. A pair of ******* turbo diesels out of a Ram would be great direct drive, just very heavy.
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the diesel engine parked outside my office at the moment (see picture) has such a "high rpm" that we had to abandon even the gearbox and attach it to a generator instead. At least, I'll bet your mercury marine guy would buy that reason.

Aside from that though, I have to express some disappointment at your use of vulgar language on this forum. Out of consideration for polite society I deleted the offending word from my quote of your post.
 

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If what he said is true, we should all limit our service ceiling to about 7500 feet. Since, above that, we would be cruising at or below 65%.

Engineers aren't all knowledgeable. Credentials don't always mean anything. If they are presented to you as some kind of proof, RUN!
 
Can running at 65% hurt,

Sure, ditch the air filter and run at 65% or less through a dust storm and I bet you will hurt it.
 
JHW said:
the diesel engine parked outside my office at the moment (see picture) has such a "high rpm" that we had to abandon even the gearbox and attach it to a generator instead. At least, I'll bet your mercury marine guy would buy that reason.

Aside from that though, I have to express some disappointment at your use of vulgar language on this forum. Out of consideration for polite society I deleted the offending word from my quote of your post.
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:rofl:

My apologies for offending your eyes.

That's a nice engine. I bet it weighs more than the 310.
 
I'm sure the presenter realized that 75% wasn't achievable at higher altitudes (non-turbo), but he was very "old school". What he advocated really isn't that far off from what the POH or Lycoming manual suggests for best power, no? His view is that aircraft engines are designed to run at these higher power settings all day long, so why not take advantage of that fact. But after reading articles by John Deakin, Mike Busch, and others regarding ROP/LOP procedures, I'm convinced there are better ways to operate your engine. I just had never heard the twist that low power settings (lugging?) could actually be harmful, especially in our low power fixed pitch Warrior.
Thanks for all your responses!
 
I've been trying to wrap my head around this, if it were reported accurately and I can only come up with a few ideas. In the 2-stroke marine world, you don't want to lug an engine because the temps won't stay up high enough to prevent oil fouling. This has been true for generations, and the oil injection has helped a bit, but it's still a problem. Of course, this has nothing to do with air cooled, 4 stroke, Otto cycle engines, but that's his background.

The other thing that comes to mind is that the power band for a 2-stroke can be peaky depending on port design, and running at low RPM and high MP can cause reversion which is a backup in the intake runner causing poor running and uneven flow through the engine. Again, this has almost nothing to do with a 4 stroke, although reversion is possible with large cam overlaps(end of exh cycle) that are found in higher RPM engines. Our engines are not peaky, and do not generally run much overlap.

The 4-stroke marine world is gaining traction, but maybe he was working in the legacy world of marine outboard 2-strokes. That's all I can figure. Cause, he's completely wrong about aviation gas Otto cycle engines. The only thing that is true is that thermodynamic efficiency is greatest where he says to run it, but that will NOT provide the longest engine life span. It will provide the greatest engine pumping efficiency, but that would translate to the greatest wear cycle as well. In his use case, you'll be putting in new exhaust components every 500 or so hours.
 
VWGhiaBob said:
Take a look at my Forum name...I know something about VW engines and you say this guy has experience with them. Perhaps that clouded his perception. VW engines are particularly vulnerable to lugging and must be kept at a moderate to high RPM's to ensure long life.
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And there you go.

You can lug an engine (low rpm, high torque) in an automobile because you can put the transmission in a higher gear and limit the engine speed. You can stomp the pedal and stay at low speeds - lugging.

You generally don't lug an engine in an airplane because you don't have a transmission connected to wheels connected to the ground. If you push the black knob in, the engine speeds up. If you have a constant speed prop, you can slow it down a bit - but running less than 65% power does not (or should not) imply running at wide open throttle and pulling the prop until you get down to 1000 rpm (assuming that is even possible).
 
Steve Job said:
I'm sure the presenter realized that 75% wasn't achievable at higher altitudes (non-turbo), but he was very "old school". What he advocated really isn't that far off from what the POH or Lycoming manual suggests for best power, no?
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No, it is that far off.

His view is that aircraft engines are designed to run at these higher power settings all day long, so why not take advantage of that fact.
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Just because it's designed to be able to run happily at 75% doesn't mean running it at 65% will hurt it. Furthermore, in pretty much any production light plane, 65% will keep your overall costs down measurably compared to 75% because you'll get more miles per gallon of fuel and more miles per dollar of engine maintenance.

I just had never heard the twist that low power settings (lugging?) could actually be harmful, especially in our low power fixed pitch Warrior.
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This person is completely confused if he things running at 65% is "lugging." That term is more appropriately applied to running at too high a manifold pressure for the RPM so the fuel/air mix detonates rather than burning evenly. But you can do that at any power setting if you run too high a MP for the RPM. Those MP/RPM limit lines are shown in the power charts in the engine manual -- for my O-360-A4K, the limit MP for 2300 RPM is something like 27 inches, IIRC (don't have the manual here). But that's an entirely different issue, and you can cause that problem at almost any % power if you pull the RPM back far enough with the MP up high. Further, it's a non-issue for fixed pitch prop production airplanes because the prop pitch is selected so that cannot happen.

To summarize, there's just no way that running at a proper RPM/MP combination for 65% power under normal operation will in any way cause any more stress on the engine or shorten its life compared to running at a proper RPM/MP combination for 75% under the same conditions.
 
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Ron Levy said:
No, it is that far off.

To summarize, there's just no way that running at a proper RPM/MP combination for 65% power under normal operation will in any way cause any more stress on the engine or shorten its life compared to running at a proper RPM/MP combination for 75% under the same conditions.
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Exactly right!

The guy needs to stick to boats and boat motors!
 
N801BH said:
My question to all the A&P's out there...

When you are studying and testing for the Powerplant rating, do you actually have to demonstrate your basic knowledge of internal combustion engines or can you just BS your way through the whole process....:dunno::dunno:.. Is there not questions on the test to confirm this?:dunno:

Personally, when I see the term ( A&P) after a persons signature I assume they are somewhat intelligent in the concept of motors... Maybe I have been wrong all these years in assuming this..:redface:
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The truth of the matter is that yes....a good test taker can easily pass the written part of the test with no problems even if he doesn't know much in real life. In fact, if the examiner is of the type to pass a student for other than realistic reasons the practical could be done too....

I think most examiners and takers of A&P tests are honest and have some reasonable ability or knowledge of mechanics. I've met quite a few A&P's from schools who should probably be working at walmart but that is likely true of a lot of car mechanics...doctors, teachers etc.....etc... or in fact any job.


I think the consensus is right though, the guy is an idiot. Cars rarely use very much of the available power of their engines and normally don't run at any real power output of more than about 20%. Having worked on race cars for a long time I can say that car engines worked hard wear out quicker than those run on the road by the average joe. Run them easy like we do going back and forth to work and they last forever. Run them like they do at the indy 500 and they last about 650 miles. (we ran them in during pre race practice and sometimes did a few miles prior to the race....)

Frank
 
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