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  #1  
Old 05-19-2022, 09:11 AM
KayS KayS is offline
 
Join Date: Jul 2009
Location: lake constance
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Default difference between mineral aviation oil and car engine oil?

Hi All, i know a guy who owns a Cessna with 140 hp lycoming. el cheapo he is, he mixes mineral aviation oil (don't recall the brand) 50:50 with even cheaper mineral oil for gasoline cars, the stuff you find in any hardware store. he inherited the airplane from his dad, who did the same since WW2. is that a good idea? or to be precise... whats the difference in these oils? could we learn here something to save some bucks on our RV operation?
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  #2  
Old 05-19-2022, 09:18 AM
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My personal opinion, this is not a place to save a few bucks. The life blood of our engines should not be sacrificed. IMHO
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  #3  
Old 05-20-2022, 06:31 AM
David Z David Z is offline
 
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Modern automotive oils aren't designed for leaded fuels, or lead contaminants. Wasn't the case post WW2 when automotive gasoline was leaded. Not suggesting it was okay then, but it's even less okay now.

Use cheapo aviation oil if one insists, but only make sure it's approved by the engine manufacturer.

Better oils will help the engine last longer. Mineral oil actually increases wear, that's why we're supposed to use it for break-in. Not unsafe to use approved aviation mineral oil for the life of the engine, but not sure there's actually any long term cost savings come overhaul time.
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  #4  
Old 05-20-2022, 07:04 AM
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MacCool MacCool is offline
 
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I don't know enough about airplane engines to know whether or not cutting that particular corner would be a bad thing for a $30,000 investment that also plays a role in keeping me alive. My initial impression is that it would be stupid given what's at stake, but maybe that's just me. I long ago came to grips with the fact that aviation is expensive.
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  #5  
Old 05-20-2022, 08:10 AM
lr172 lr172 is offline
 
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Not something I would do and I always look for a way to save a buck. Aviation oils have significant dispersent packages in order to handle the load of lead deposits that find their way into the oil. Auto engines do not have anywhere near the load of debris in the oil that our engines do and therefore have fewer dispersents. Once you have exceeded the load that your oil's dispersent package can handle, that junk ends up as sludge everywhere and over time can create real problems. Auto oil also has detergents and that is a no no for engines burning leaded fuel. It will help release any sludge build up and send it to places you don't want it.

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Last edited by lr172 : 05-20-2022 at 08:14 AM.
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  #6  
Old 05-20-2022, 09:09 AM
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The engine experts that I've read/watched (Busch, Braly, Kollin) say if you use only unleaded fuel - which is easy to get in most parts of Europe - then using automotive engine oil might be superior to aviation oils. No lead means you can run fully synthetic oil without the "lead sludge" problem.

The challenge I have is when I travel, some places only have 100LL, so I'm sticking with aviation oil. Not to mention that where I live, aviation oil and good quality automotive oil are about the same price.

There are lots of good videos with these guys talking about engine oil, this is a really good one featuring Ed Kollin of Camguard fame: https://www.youtube.com/watch?v=Ia-zgGr2pKg
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  #7  
Old 05-20-2022, 09:23 AM
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Roadjunkie1 Roadjunkie1 is offline
 
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Default Auto vs Aviation oils.....

From Aviation Stackexchange:

Aviation and automotive engines work on the same basic principles, but many of the details are different. One significant difference is that aviation engines normally burn some oil as they run, while well-performing automobile engines burn little or none.

Automotive oil contains a number of additives, such as detergents and wear inhibitors, intended for use where the oil doesn't burn off. Some of those additives do not burn completely, but instead stick around in the form of ash, where they can foul the engine and create deposits that lead to pre-ignition. That is why aviation oil is ashless dispersant: it cleans the engine by dispersing combustion byproducts into the oil (to be removed on the next oil change), while being ashless when burned. Lycoming considers it serious enough to put in an all-caps "CAUTION" section in their Lubricating Oil: UNDER NO CIRCUMSTANCES SHOULD AUTOMOTIVE OILS BE USED......CAN CAUSE ENGINE FAILURE.

From AvWeb:

While it is true that automotive oil is far more advanced than aviation oil, the answer lies in the fact that most aircraft engines are air-cooled while automotive engines are water-cooled. Air-cooled aircraft engines are built with greater clearances and are designed to consume (burn) some oil. Water-cooled automotive engines are designed and built to much tighter tolerances, so they do not consume much oil. These differences in design tolerances are due to the large temperature differentials that are found in high-continuous-power-output, air-cooled, aircraft engines versus the low- and intermittent-power-output, water-cooled, auto engines. There can be a 300 degree F temperature difference between the cylinder head and cylinder base in an operating aircraft engine. That kind of temperature differential causes a lot of distortion in the cylinder, necessitating the requirement for large clearances. Automotive engines, being water-cooled, have lower temperature differentials across the engine and thus suffer lower levels of distortion and can be designed and built to tighter tolerances. Aircraft engines were designed before additives were available and have not really changed much over the years. When ashless dispersant oils were introduced for auto engines, they were also suitable for aircraft engines and eventually were adopted for aviation use. However, when zinc antiwear and metallic detergents were formulated into auto oils, an important divergence occurred. Aircraft engines burn a fair amount of oil and, if these metal-containing detergents and antiwear compounds are present, they can form metallic ash deposits in the combustion chambers. These deposits can lead to destructive preignition, which could burn holes in the tops of pistons with obvious catastrophic results. For that reason, it was decided that aviation oils were to remain ashless to avoid the risk of metallic deposits. The benefit of using ashless dispersant oils is, obviously, a cleaner engine. Aircraft engines would also benefit greatly from the addition of other automotive additives such as anti-wear, detergents, and corrosion inhibitors, but the downside is added cost. Ashless versions of these performance additives can cost up to 10 times more than standard ash-containing additives.

Being part Scottish, I look for ways to decrease flying expenses. Using auto oil is NOT one of them......
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  #8  
Old 05-20-2022, 10:14 AM
agent4573 agent4573 is offline
 
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Not that I agree with doing this, but you guys keep mentioning the dispersant and additives. OP clearly said mineral oil, and both Phillips and aeroshell claim non-dispersant and aeroshell explicitly says it has no additives in it's mineral oil. I realize there is still a huge difference between automotive and aviation oils, but the comparisons so far in this thread are making claims on the wrong type of aviation oil.
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  #9  
Old 05-20-2022, 10:59 AM
lr172 lr172 is offline
 
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Quote:
Originally Posted by agent4573 View Post
Not that I agree with doing this, but you guys keep mentioning the dispersant and additives. OP clearly said mineral oil, and both Phillips and aeroshell claim non-dispersant and aeroshell explicitly says it has no additives in it's mineral oil. I realize there is still a huge difference between automotive and aviation oils, but the comparisons so far in this thread are making claims on the wrong type of aviation oil.
just about ALL commonly used aviation oils, mineral based or otherwise, except specific, "break in oils" use ashless disspersant additives. Calling it "mineral oil" means that the base stocks are mineral based; It does not mean that it does not contain AD's. Generally, a mineral oil without AD's is called "straight mineral oil." I wouldn't be surprised to find that oil manufacturers do not consider AD to be an additive. But that doesn't mean their mineral oil doesn't contain AD's. Please site a reference for a non break in oil that does not contain ashless disspersents. I think you will struggle to find one that isn't a small volume fringe product or classified as a break in oil. You NEED dispersnets to hold the lead particles and other blowby particles in suspension to avoid sludge issues in any engine running leaded gasoline, even more so with air cooled engines that have more carbon blowby. Ask Lycoming or continental if they recommend running their engines on straight mineral oil without AD's outside of the beak in period. Please read the first two paragraphs of this Lycomind document to avoid the suspense:

https://www.lycoming.com/content/oil...il%20additive.

Quote:
Many Lycoming engines use straight mineral oil for “break-in” purposes with a new, rebuilt or overhauled engine. The operators should then switch to AD oil after “break-in” has been accomplished...

Since modern FAA-approved ashless dispersant oils already include additives that make them superior to straight mineral oil, the use of additional oil additives in Lycoming engines has been very limited...
Larry
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Last edited by lr172 : 05-20-2022 at 12:02 PM.
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  #10  
Old 05-20-2022, 11:48 AM
swjohnsey swjohnsey is offline
 
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About $6/qt.
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