Engine Oil Design

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Skippydiesel

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That is not correct. The by-pass valve prevents oil starvation when cold, thick oil is clogging the cooler. It also prevents oil starvation if the cooler becomes clogged with debris/sludge. Dependant on the susceptibility of the cooler to these issues, the latter functions can be vastly more important than a fast warm-up. The by-pass does need to be checked, including for correct orientation. Removal for test purposes is reasonable. However, the first priority in this instance is check and calibration of the instrumentation - replacing the instrument does not in itself assure that the temperature data is correct.
Don't know what oils you are using , under what conditions but your knowledge would seem to pre date the use of multigrade & synthetic oils. Sludge? Cold . thick oil? - ancient history my friend. We now have oils that start at 0 (not that I like the idea) that pour like water, when cold and detergents that have consigned "sludge" to the memory of my youth.
 

rv7charlie

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Don't know what oils you are using , under what conditions but your knowledge would seem to pre date the use of multigrade & synthetic oils. Sludge? Cold . thick oil? - ancient history my friend. We now have oils that start at 0 (not that I like the idea) that pour like water, when cold and detergents that have consigned "sludge" to the memory of my youth.
Apparently you don't own an airplane; only cars & trucks. Current airplane tech *is* ancient history.
 

Pops

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In the 1950's, oil was so bad I would have to take a screw driver and punch an opening in the sludge in the oil pan opening after taking the drain plug out when I changed oil. Then pour kerosene in the engine to wash the sludge out of the pan. Take the valve covers off and sludge would cover all the rocker arms.
High mileage engine would be 50K. Lots of bug dusters on the road.
 

TFF

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Mixing Texas and Pennsylvania oil use to be a problem. Sludge city. My first boss didn’t believe in oil changes Delivery vans got replaced at 100k so fewer the better. I remember one van stopped running at 80,000 miles. When they took the valve cover off, there was a perfect internal mould of the cover. One block of crunchy stuff.

You are not going to put 0 weight oil in a Lycoming. Air cooled are just too hot and clearances have to be too wide because of it. I’m a fan of the Phillips 20-50 because of cold start. I would love an Aeroshell version that wasn’t semi synthetic. Not a fan of theirs. Aeroshell 100 is hard to beat except it being straight weight.
 

D Hillberg

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After 'overhaul' was the engine properly broken in, in accordance with the engine manufactures procedure?
Had a few Aircoups that worked for a few hours then petered out after overhauls because the owners just didn't know...
Ran good in Alabama then Hot running lack of power in New Mexico???. A few hours??? Top End?
Snort Bon ami scouwering powder
There was a break-in abrasive compound for small 2 stroke model airplane engines many many decades ago called Fox Lustrox. You were supposed to put a tiny coke spoon's worth of this stuff on the edge of the carburetor venturi, and it would slowly siphon off a tiny little bit at a time over a mnute or two, and then "break in" (or hone or polish, whatever) the engine internals.

But using abrasive like Bon Ami in a full size 4 stroke aircraft engine... that sounds like a recipe for getting abrasive into all sorts of parts that you don't want abraded. Bearings, bushings, cam lobe faces, hydrauic lifters, gears... OMFG... Don what'cha been snorting up there in the desert?
It goes in the intake through the top end and out the exhaust - Works great when out at the track -
On O 85 through O 200 too. But seriously this looks like a missed break in after overhaul
 

Dan Thomas

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I would love an Aeroshell version that wasn’t semi synthetic. Not a fan of theirs. Aeroshell 100 is hard to beat except it being straight weight.
I ran Aeroshell 15W50 in all the schools airplanes, Lycs and Continentals, and those engines all easily went to TBO. Our cold weather limit was -25°C (-13°F), and we had a heated hangar for overnight storage. Threw an insulated cowl cover over the cowl after a flight if the airplane was going to sit for an hour two two outside before the next flight. Max ambient temps were as high as 35°C (mid-90sF) at the home base, and up to 40°C (102°F) on long trips elsewhere in the summer. That oil worked marvellously for us.
 

TFF

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We had to run multi weight oil for our turbocharged helicopters. Recommend for our application. We preheated when in hangar, but the helicopters did travel and had plenty of ramp time. Plenty of hot summers. We had rings stick on some cylinders. We were told not to use that oil. Coincidence or problem? There are people in both camps that are good people. The guys in the desert southwest get to run Aeroshell 100 in this application which is what we ran in the non turbo versions. Oil discussion is no different with cars. I learned that with oil, everyone is 100% right and 100% wrong 100% of the time.
 

Skippydiesel

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Apparently you don't own an airplane; only cars & trucks. Current airplane tech *is* ancient history.
I am on my second aircraft, both Rotax 912 ULS powered - I use AeroShell Sport 4 and have never experienced sludge build up or problems with cold engine/oil distribution.
Oh! and I am a diesel engine fanatic cars/ 4 x 4's/ tractors, all diesel - no oil issues there either.
 

TFF

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Airplane buildup is used different than car sludge. Old style oil, deposits were intentional. Instead of having the chunks circulate, it was supposed to deposit and get cleaned out at overhaul. Adding Marvel to keep the engine clean was against how the oil was formulated.

Rotax run car oil or motorcycle oil. Running a Rotax is not running a Lycoming or Continental oil wise.
 

Skippydiesel

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Airplane buildup is used different than car sludge. Old style oil, deposits were intentional.
Intentional - I very much doubt it.
I am from the generation that had to "de-coke" land based engines, on a distressingly regular basis. I remember what the inside of a pre detergent (ashless dispersant ?) oils engine looked like - yuk!. I also recall it was thought that running a petrol engine on diesel (high detergent) oil from the start of its life would prevent all this accumulation of "gunk) but you could not use such oil on an engine that had run up a few thousand miles, least its bearings & journals might get sloppy and it would start consuming prodigious quantities of oil.

Instead of having the chunks circulate, it was supposed to deposit and get cleaned out at overhaul. Adding Marvel to keep the engine clean was against how the oil was formulated.
Yes - Back in the olden days, we also had engine flush mechanics in a bottle - seems to me better to prevent the problem from happening in the first instance by using an appropriate oil.
Rotax run car oil or motorcycle oil. Running a Rotax is not running a Lycoming or Continental oil wise.
Rotax 9 generation aircraft engines are certainly far in advance of LyCons - more efficient, cleaner exhaust/less polluting and by enlarge go well past their TBO, without costly interventions. Helping them in this, is their use of modern crankcase oils, that don't gunk up the internals.
 

Dan Thomas

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Rotax 9 generation aircraft engines are certainly far in advance of LyCons - more efficient, cleaner exhaust/less polluting and by enlarge go well past their TBO, without costly interventions. Helping them in this, is their use of modern crankcase oils, that don't gunk up the internals.
Lycomings and Continentals that are run regularly and maintained properly can easily run way past TBO. There are 4000-hour examples out there. The smaller Lycs (up to the -360 series) are almost bulletproof and need little or no valve work in 2000 or more hours. I ran a lot of O-320s in flight school airplanes and none of them needed valve work in the entire TBO period. The things that DO need periodic care are the magnetos, alternators and vacuum pumps, things that owners stupidly tend to run to failure.

The larger Lycs and Continentals typically need valve work around mid-time. That's to be expected in an engine generating 230-300+ HP. Rotax has no engines like that and so of course their valves and other stuff last a long time. Apples to oranges.
 

PMD

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The larger Lycs and Continentals typically need valve work around mid-time. That's to be expected in an engine generating 230-300+ HP. Rotax has no engines like that and so of course their valves and other stuff last a long time. Apples to oranges.
Rotax 912 ULS 100 HP 1352cc (82.5 cu. in) 74 BHP/litre = 1.2 HP/cu.in.
Lyc IO540 - 300 HP - 26 BHP/litre = 300 0.55 HP/cu.in.
Cont IO550 - 310 HP - 34 BHP/litre 0.56 HP/cu.in.

Rotax 912 @ 129 lbs. = 1.29lb/HP
Lyc IO540 @ 438 lbs. = 1.46 lb/HP
IO 550 @ 491 lbs. = 1.58 lb/HP

Comparing normally aspirated to normally aspiratted - you're right, Rotax could only be compared if they took a plug wire or two off. I may not LIKE them, but I will give the Devil his due.

Having come from a lubrication background in my downstream life, I concurr that modern auto engine oils are far advanced and asked to do far more things than aviation oils. Ancient aviation straight grades suffered from extremely poor oxidative stability of their base stocks and timidity of the industry to use correct additive chemistry, never mind synthetic base stocks.
 

Skippydiesel

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Lycomings and Continentals that are run regularly and maintained properly can easily run way past TBO. There are 4000-hour examples out there. The smaller Lycs (up to the -360 series) are almost bulletproof and need little or no valve work in 2000 or more hours. I ran a lot of O-320s in flight school airplanes and none of them needed valve work in the entire TBO period. The things that DO need periodic care are the magnetos, alternators and vacuum pumps, things that owners stupidly tend to run to failure.

The larger Lycs and Continentals typically need valve work around mid-time. That's to be expected in an engine generating 230-300+ HP. Rotax has no engines like that and so of course their valves and other stuff last a long time. Apples to oranges.
Hi Dan,

Me thinks you make my point in your list of such interventions as "valve work" and although you didn't mention it , the occasional cylinder, piston, etc may also need replacing.

As for owners/operators not managing an engine as they should - this will be much the same across all engines.

Its interesting (to me at least) that most well maintained Rotax 9's will easily exceed TBO, without anything more than a mid life gearbox check (some cutch parts may be replaced). Few (this does not mean none) LyCons will make it to TBO without things like "valve work", cylinder replacement, rings, etc To me this constitutes "major surgery " and yet the faithful say the engine has made /exceeded TBO without intervention - go figure!

If you are going to compare apples with apples the comparison should remain within the same approximate hp range.
 

Dan Thomas

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Hi Dan,

Me thinks you make my point in your list of such interventions as "valve work" and although you didn't mention it , the occasional cylinder, piston, etc may also need replacing.

As for owners/operators not managing an engine as they should - this will be much the same across all engines.

Its interesting (to me at least) that most well maintained Rotax 9's will easily exceed TBO, without anything more than a mid life gearbox check (some cutch parts may be replaced). Few (this does not mean none) LyCons will make it to TBO without things like "valve work", cylinder replacement, rings, etc To me this constitutes "major surgery " and yet the faithful say the engine has made /exceeded TBO without intervention - go figure!

If you are going to compare apples with apples the comparison should remain within the same approximate hp range.
Believe what you want, but my engines ran to TBO with no valve work. The only Lyc that gave trouble was the O-235, an engine that runs notoriously cold and suffers crankcase condensation that takes a long time to boil out, and most flight school stuff is one-hour flights. That moisture caused cylinder wall pitting that resulted in the rings leaving a ridge at the bottom of the travel, and the ridge chipped away at the piston pin plugs. At mid-time the cylinders had to come off and get cleaned up and go back on. I blocked off the airflow through the oil cooler and got better results.

Those O-235s were in Citabrias, and maybe the Citabria cooling system was a bit too powerful. Cessna 152s used those engines and had no reputation for cylinder ridging.

One mechanic I worked with maintained Rotaxes in DA20s. He hated them, said they were troublesome things. Diamond eventually replaced the Rotax with a Continental IO-240, which says something.
 

challenger_II

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One of the issues with the Diamond engine change matter: some major flight schools found the 912's to be a tad gutless for the purpose. Also, they were maintenance pigs.
 

Tiger Tim

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Airplane buildup is used different than car sludge. Old style oil, deposits were intentional. Instead of having the chunks circulate, it was supposed to deposit and get cleaned out at overhaul.
I always thought the sludge buildup was to plug all most of the leaks 😂😂
 

PMD

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If you look at a 912 or any other Rotax 4 stroke, you can not help but notice all of the crap hung off of the engine with precariously high mass at long moment arms. No wonder they are maintenance hogs! I use them as a worst case example on how NOT to build an A/C engine.

To address Dan's point about 0-320 operating temps: it is not the engine that is the problem, it is the deplorably bad cowlings from OEMs until the last few decades (i.e. until Roy Lopresti made them pull their heads out of the collective rectae (is that the right Latin plural????). One of the MANY reasons water cooled engines work and last so much better is there is a thermostat controlling engine temps vs. virtually NO control on legacy air cooled cowling systems. We used to block off oil coolers and often air inlets when operating in the Northern winters - and got reasonable engine life.

Sorry if I sound a bit harsh on that count, but I believe that the O-320 (other than H2AD) is possibly overall the best engine so far installed in any airframe.
 

Paul Saccani

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Don't know what oils you are using , under what conditions but your knowledge would seem to pre date the use of multigrade & synthetic oils. Sludge? Cold . thick oil? - ancient history my friend. We now have oils that start at 0 (not that I like the idea) that pour like water, when cold and detergents that have consigned "sludge" to the memory of my youth.
Dear Skippy, those (clearly, synthetic) oils are entirely inappropriate to this engine when using AVGAS. In fact, they are deadly. Only the base mineral oil is able to suspend the lead compounds in cylinder blowby, synthetics drop it out of suspension in ways that block oil galleries. The typical oil used is a 100 or 120 monograde ashless dispersant, corresponding to SAE 50 and SAE 60. Detergent oils are completely out of the question. In point of fact, they are OBSOLETE in aviation oils mainly due to the hazards they create. Multigrade aviation oils are available too - for a number of reasons, they are not as popular as you might think they should be. In certain parts of this engine, oil can reach rather high temperatures (notably in the rocker box on the exhaust valve side), resulting in oxidation and sludge formation, but there is also the sludge produced from blowby lead products to consider. These high temperatures can result in degradation of the viscosity modifiers used to maintain viscosity at higher temperatures in multi-grade oils - dependent on individual installations and operations, in many cases it never happens at all. Gasoline oil dilution and/or pre-heat allows mono-grade oils to be used in cold environments. Please do consider whether or not your automotive tribology knowledge actually crosses over to aviation engines - in many cases, it is most inappriopriate.
 
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