Does anyone have first hand experience with an engine problem they believe, or was told by their mechanic, to have been caused by habitually operating their engine at less than 75%?

I’m still kinda in the “Which Plane” conundrum but getting a little closer to figuring it out. It’s comming down to a 180hp or 235hp, and probly one of those in a Maule.

I currently live in central WI but my wife and I will probably move out to Alaska in a handful of years to be closer to our son who lives there. Hopefully they won’t be full by then! We want to live the dream of using the plane like an SUV for camping, fishing, hunting, and would still like reasonable T/O and LDG performance. I prefer to fly slower and enjoy the view rather than ballz to the wall. I’m not too excited about feeding a bigger engine. So the smaller engine would make sense, But, I also don’t want the smaller engine to limit certain strips where we could land due to being tight on getting out loaded-up.

I’m sort of leaning towards the bigger engine because guys talk about how they can power down and get 8 or 9 gph and still have that extra HP for when they need it. But is it good to consistently run an engine like that?

I appreciate your input!
Bill

I don’t have any long term data for you since I’ve only had mine for a year (MX-7-180A), but I run mine less than 75% most of the time. Mainly because it gets quite noisy at 75% (2450 RPM) and it’s exhausting to fly with that noise over time. The engine has almost 1300 hours on it, and compression checks have been perfect for the last couple of annuals and oil remains clean. Fuel burn is certainly favorable as well. The previous owner flew it similarly, but he did run the plane harder than I did at times, being an aerial photographer and had a lot of fun with the plane. I’m still sorting it all out.

~Chris

P.S. - If I had the option, I’d choose the 235

If it were my choice I’d go bigger, too.

My O-320 is run less than 65% most of the time. I’m hardly in a hurry to get places and enjoy the scenery.

Plus I do a lot of local putting around at low power.

Even on 100LL, I haven’t had any issues. I just lean appropriately for the condition and enjoy the sights.

Running an engine below 75% will hurt it? -Pure hogwash! As long as the cylinder head temps are kept at a reasonable temp to maintain good combustion and the oil temp is not too cold, the engine will run just fine long term. It's the same as running as a derated model. There are several Lycomings that are the same basic core engine, but are designated as different models depending manifold presure limits/RPM with the lower rated units having longer TBO.

I’ve run all kinds of aircraft engines at less than 75% regularly, with no adverse effect.

Consider that with most engines, if you are at a density altitude of about 5000 feet or more, most normally aspirated engines aren’t capable of developing 75% rated power. Here where I live, 500 agl gets you there on a standard day.

So, there are a LOT of piston engines being operated routinely below 75%.

I’d be more concerned over operating routinely at OVER 75%. But I wouldn’t sweat that too much either..... .

MTV

The other Underwood Aerial Patrol guy who flew out of 2H2 with me also regularly overhauled at 3,000 hours. Unlike me who landed every two hours in my 150 hp 172, he liked to go five hours with zip lock bags in his 180 hp Cardinal. He ran 2500 rpm (we need the turns down low) and 21 inches of manifold pressure. He used just a little over 8 gph.

No it doesn't seem to hurt the engine. Down low you need full power quickly when between a rock and a hard place, however.

I used a little more gas in a smaller fixed pitch engine, but Murphy and me didn't trust zip lock bags. I also ran 2500 rpm.

Was out chasing coyotes with a neighbor the other day me in the cub(O-320) and he in the husky(O-360). I cruise at 65-70mph on the lookout. Later asked the Husky owner why he would not stay that slow and his response was similar in that he was told it was bad for the engine. He implied that this was suggested by his operating manual but did not specifically say that. Or is it an old wives tale. I was curious as this did not make sense to me.

Coyote wrote:Was out chasing coyotes with a neighbor the other day me in the cub(O-320) and he in the husky(O-360). I cruise at 65-70mph on the lookout. Later asked the Husky owner why he would not stay that slow and his response was similar in that he was told it was bad for the engine. He implied that this was suggested by his operating manual but did not specifically say that. Or is it an old wives tale. I was curious as this did not make sense to me.

One of the beautiful things i've seen in aviation is hours and hours of running a Husky at 1950 rpm and 20 to 21 inches of MP. That's a pretty low power setting, but it works. Holy crap, if that wive's tale were true, I'd have used up a bunch of Husky engines. My job was operating low and 65 to 70 mph for hours on end with them.....

Have your friend call Lycoming Tech services, or better yet, tell him to get on the Husky web forum and learn from those guys.

MTV

Two Points:

One, In a Maule with high performance airframe characteristics it needs a high performance motor. As an owner of a perfectly capable 180 HP, I recommend the 235 or the 260 if at all possible. In the backcountry, power improves safety and utility. A lot.

Two, I run my 180 at 55-65% quite a bit also. Many flights I'm just savoring the time aloft and in no rush for the pleasure of flight to end. If I lean aggressively the plugs won't foul.

mtv wrote:I’ve run all kinds of aircraft engines at less than 75% regularly, with no adverse effect.

Consider that with most engines, if you are at a density altitude of about 5000 feet or more, most normally aspirated engines aren’t capable of developing 75% rated power. Here where I live, 500 agl gets you there on a standard day.

So, there are a LOT of piston engines being operated routinely below 75%.

I’d be more concerned over operating routinely at OVER 75%. But I wouldn’t sweat that too much either..... .

MTV

I think the 75% max power at WOT thing starts at 7,500' DA, FWIW.

I think there's a TCM SB cautioning against running at low MP.
I checked it & it doesnt apply to my 470K.

Go for the higher horsepower if you can.

Of all the machines I've ever bought I've never once wished I had gone for the smaller engine model.

hotrod180 wrote:I think there's a TCM SB cautioning against running at low MP.
I checked it & it doesnt apply to my 470K.

Found it, turns out it's against low RPM ops- not low MP. Here's a link:

https://www.twincessna.org/pdf/TCMCSB09-11(MinCruiseRPM).pdf

TCM originally issued SB07-8 & 07-8A, this SB09-11 supercedes them.
Here's the guts of it:

"Effective immediately, TCM strongly recommends the following limitation be observed on all the models affected above:
Engine cruise RPM settings should be no lower than 2300 RPM. NOTE … This limitation applies only to cruise operation and is not meant to supersede the aircraft manufacturers’ recommendations for other operational modes such as emergency or holding procedures."

Click the link to see engine moels affected.

At one point while I was running Huskys pretty regularly, the question of running engines "over-square" came up. Over-square meaning running the rpm at a relatively low number, compared to the manifold pressure. So, for example, 1900 rpm and 21 inches is considered "over-square".

So, I contacted Lycoming Technical Services, and asked them the question. Specifically, I asked if operating over-square could damage an O-360, and secondly, how much over-square was approved. None of the provided power charts for the O-360 showed any over-square settings. Their response was that "No, operating an O-360 over-square will not hurt anything, and they provided a power setting chart, which showed limits for over-square power settings. It was obvious that it simply wasn't physically possible exceed those limits.

Consider that turbo charged and supercharged engines routinely run over-square power settings as well.

Many O-360s run over-square very nicely.

So, another wives tale down the tubes.

MTV

Then there is the red zone for certain Lycoming/Hartzell combinations to consider. I'm not sure those exist with newer propellers.

Mountain Doctor wrote:Two Points:

One, In a Maule with high performance airframe characteristics it needs a high performance motor. As an owner of a perfectly capable 180 HP, I recommend the 235 or the 260 if at all possible. In the backcountry, power improves safety and utility. A lot.

Two, I run my 180 at 55-65% quite a bit also. Many flights I'm just savoring the time aloft and in no rush for the pleasure of flight to end. If I lean aggressively the plugs won't foul.

Thanks for sharing your experience with your 180 Mountain DR. I spoke to Aero101 over at the Maule site about his MX-180 fixed pitch. I think it is the “180 A” model Maule. It seems he was very happy with his ship and the 80x44 prop. I haven’t looked into what prop that model normally comes with.

I like the capability of the 235. I just don’t want to, actually I can’t afford to feed it 12-14 gph all the time. So that’s what raises my concerns about loafing around at the lower power setting as habit.

I haven’t checked into average overhaul cost between the lyc 180 f/p, 180 c/s, and 235 hp engines either. When I do, that may also sway me to one way or the other.

Currently I’m in a flying club with a piper warrior. The annual just finished up. The mechanic said he found ALOT of fouling at the lower plugs. He used a dental pick to break the lead free. The chunks were rather large. I routinely fly at about 55- 65% power and lean aggressively. But I don’t know how the other 9 members in the club fly it. Its a Lyc 320.

BTW..Chris in Marshfield, Alan the mechanic at WFS says hi! Your name came up when I was talking about Maules with him. Hope your transition down to the Milwaukee area went well!

Bill

billjesstaylor wrote:BTW..Chris in Marshfield, Alan the mechanic at WFS says hi! Your name came up when I was talking about Maules with him. Hope your transition down to the Milwaukee area went well!

Bill

Hi back, to you and Alan both!

Transition has gone well, and I have a great maintenance organization down here at Timmerman that is happy to allow me to work alongside them on the Maule. We're all learning a little something every time we work on it!

Good luck with your decision. As you mentioned earlier, the 180FP is a good choice for these flat lands and frozen tundra. But once you're up in the mountains, those two extra cylinders would certainly be welcomed, I imagine! I've never been in them, myself. But plenty of info here from the folks that live in those environments tell the story.

Bob Barrows, the Bearhawk designer, tells us that it's easy enough to pull the power back on a 540 and burn the same amount of gas that we would with a 360. It's really a matter of how fast to you want to go. Maules have a fairly low terminal velocity, even with a big motor.

Good to hear Chris!

Yeah a guy can give himself an ulcer over analyzing these things. I think I’ll just have to catch a ride in the different models. No doubt all will give me a big grin. But more than likely I’ll go with whatever gives me the biggest and try to find a way to pay for it. Gotta Pay to Play right?

billjesstaylor wrote:Does anyone have first hand experience with an engine problem they believe, or was told by their mechanic, to have been caused by habitually operating their engine at less than 75%?

...

Bill

I'm in the middle of the second run on my O360 180 hp engine. Except during takeoff and climb I'm running it at about 65%. FWIW, both Lyc and Cont tech notes say engine longevity is better, and maintenance is lower when the engine is run below 75%, and when it's run regularly in the air and at normal ops temps. I've heard the same story from company tech reps at Oshkosh and Lakeland. FWIW, lower power settings manage heat better, and also burn less gas per mile flown. Even if we're in a hurry, the marginal increase in airspeed for running WOT isn't that great. Besides, any time we've climbed over 6,000 feet or so we're running below 75% even with the throttle firewalled. From my read of the tech notes running at 75% plus "because they were designed to" is an OWT with no basis. If a mechanic tells me "that's the way to do it" I'd go find another shop to work on my equipment. No telling what other OWT they believe as they turn wrenches on my aircraft.