• If you log in, the ads disappear in the forum and gallery. If you need help logging in or getting registered, send request to: webmaster@southernairboat.com



Well-known member
I've heard lots of reasons to only run aviation oil in aircraft engines but know of a few who run auto oils in their a/c engines...How many of us know someone who does or do in our own engines and have you heard of any ill effects??
Yes JD,
I know some who run automotive oils in A/C engines, and claim no ill effects. Perhaps they are correct. I prefer to use av-oils, and heres why.

The main thing about the additive package in Ashless Disspersent Av-oils is the ashless component.

These additives are designed to help prevent carbon deposits in the combustion chambers that will glow under normal operation.

That's the ashless part.
The disspersents are the detergents, that help suspend contaminents in the oil, so they may be swept out at oil change time.

It is my understanding that extended use of automotive oils in A/C engines may cause a build up of carbon deposits in the combustion chambers that are prone to glowing under heat, like a glow plug.

These glowing embers will help pre-ignition of the intake charge, and detonation symptoms may set in because of it.

Av-oils will also leave carbon deposits, but they are less prone to glowing, and less likely to cause detonation.

That is my understanding of why you should pay more of A.D. Aero-oils.
Perhaps it's all just a sales pitch like buying insurance, but that's the info I read in an article from a retired chemical engineer on an aircraft site someplace.

Like many other apsects of A/C engine mantenance, it's all about getting good power, without harmfull detonation. You can run good fuel, have spot on ignition timing, perfect fuel metering, ext, then have detonantion due to glowing carbon depositis from running auto-oil.

I prefer the Shell Aero-100 plus, as it has the approved anti-wear additive in it right from the can.
That's pretty good info. I just had my cylinders rebuilt. When I tore down the carbon was built up in combustion chamber and on top of the pistons.
I was wondering about that.
i used auto oils for years. i just thought my 540 was 'supposed' to run like that......after i switched to aeroshell, my engine quit smoking, quit burning oil completely and did not foul plugs. it was like day and night. anyways, the aeroshell is cheaper than the oil i was using....
Another issue with aviation oil is the aircraft motors contract and expand much more then automotive. Their main bearing clearances can change up to .002 between cold and hot they run a loose bearing clearance compared to an automotive motor and this is why aircrafts run such thick oil as 50 weight and up. If you run 50 in a automotive engine that has .0015 bearing clearance your pressures will be too high and you will shear your oil causing your oil temps to go thru the roof. Also like Cowboy stated the aircraft motors are intentionally designed to consume oil thru the valve guides and past the rings and pistons. This burns allot of oil and you want a aviation oil to prevent carbon build up under these conditions. In automotive engines you try to prevent oil from interning the combustion chamber so oils are not designed with combustion chamber build up in mind. I have built a few aircraft motors and ran Valvoline straight 50 or 60 weight with no problems and know several other people who do the same. I think in an airboat it's more of a preference. Most of the aircraft airboat engine builders I know try to control the oil entering the combustion chamber more then the factory does with better rings and valve seals. There is a lot of power to be gained by this and you can drastically increase your compression ratio because a motor will be allot less prone to detonate when you remove oil from the combustion chamber.
Cowboy, I never use Aeroshell Plus in any of my aircraft. It has an additive that was put in to overcome a Lycoming cam problem on the O-320 H engine. Here's an article from Skyranch;


Do straight mineral oils have the same low temperature flow as straight ashless oils?

No. Due to the additive technology in ashless dispersant lubricants like AEROSHELL W Oils, the flow characteristics of each grade are roughly equivalent to the next higher straight mineral oil grade. For example, AEROSHELL Oil W 100 will flow at low temperatures about the same as AEROSHELL 80.


Are single and multi-weight oils compatible

The compatibility question covers two issues: mixing one type of oil with another; and the effects on the engine of changing from one type to the other.

If you typically run on multi-grade, and you find yourself in a place where only single grades are available, you can safely add the single grade to your engine. They are completely compatible.

If you run on a single grade during the summer, but want to switch over to 15W-50 for the winter, you can safely replace the straight weight with the multi-grade at your regular drain interval.

The idea that you have to stick with the type of oil you started with comes from the days unusual chemistry was done and was incompatible.

All approved MIL-L-22851/SAE J-1899 and MIL-L-6082/SAE J-1966 oils are compatible. For example, if you have a high-time engine run on ashless dispersant oils and need to replace a cylinder, you can switch to a mineral oil for 50 hours or so to break in the new cylinder. The only time I recommend against switching is in a high-time engine run exclusively on straight mineral oil. Here a switch to ashless dispersant oil can loosen deposits left behind by the mineral oil.


What is Phillips Type M oil

Type M is Phillips multi-viscosity mineral oil


What is meant by the term detergent and non-detergent

Detergent and non-detergent are not used anymore.

"Detergent" is replaced by "Ashless"
"Non-detergent" is replaced by "mineral"

Mineral means a non-additive version of regular Ashless oil used during new engine break-in


What is the difference between 50 weight and 100 oil

Aircraft engine oils (except multi-grade oils) are duel rated:

SAE 40 is the same as 80
50 is the same as 100
60 is the same as 120


What is Aeroshell Plus Oil

Aeroshell Plus is Aeroshell oil with the Lycoming LW-16702 oil additive. Lycoming '76 series engines (engines such as the O-320H2AD) require LW-16702 per an airworthiness directive to prevent camshaft lobe galling. By offering the additive as part of the oil it simplifies AD compliance and assures that the oil receives the additive.

LW-16702 is classified as an "EP" (extreme pressure) that is a surface reactant that chemically combines with Fe forming phosphides or phosphates. This protective film is a few molecules deep, that is swept away by shearing friction, and renewed thereafter. Thus LW-16702 is, in a sense, actually corroding the metal surfaces, however slowly.

Because the reacted metal surface has low shear strength, the sliding friction is markedly reduced, and the tendency to severe adhesion is reduced or even eliminated.

The combination of a higher surface energy of the freshly worn surfaces, local high temperatures, possible catalytic effects and any other activation processes makes the action of LW-16702 specific, taking place preferentially at the wear points (surface irregularities) where it is most needed.
I'm with you there I think 90% of the oil debate is based on things that no longer exist or have been changed. I think a lot of airboaters think their motor will blow up if they use Valvoline straight 50. It's like the old Quaker state formula they changed decades ago. Anyway if you change your oil regularly and your motor is in good condition you will be fine. If you have an old smoking knocking motor run the Areoshell to help keep down combustion chamber deposits which your going to get anyway no matter what oil you run.
I found this on the Shell Oil/Aviation site

AeroShell Oil W100 Plus - the premium single grade aviation oil.

Single grade Ashless Dispersant Engine Oil:

AeroShell Oil W100 Plus is a new single grade oil that combines proven AeroShell ashless dispersant technology with advanced antiwear additives. It is the oil for pilots who want a single grade that delivers extra protection and performance. AeroShell Oil W100 Plus brings together the best qualities of two of the world's best-selling four cycle aviation oils. It has the single grade, ashless dispersant performance found in AeroShell W100 and the anti-wear/anti-corrosion additives of AeroShell Oil W 15 - W50 Multigrade. It's single grade heritage means outstanding resistance to heat, especially in the summer months. Its ashless dispersant formulation reduces deposits of harmful metallic ash in combustion chambers. And its advanced additives work against rust, corrosion and wear in a way no other single grade does. There simply is no better single grade aviation oil.

Check this out...

Cowboy, I did some checking and I was wrong about not using Aeroshell Plus in my aircraft engines. I use Aeroshell 15-50 in my Cessnas and I just found out that oil contains the Lycoming Additive LW 16702. The Lycoming Additive LW 16702 is what the PLUS is in the single weight oil.

This site sure makes a guy learn a lot.
So Des,
What's your opinion on the ashless / glowing deposits thing?

That's the main reason why I thought it important to run AV-oils.

I was looking forward to your take on that point.
Perhaps you said it above, and I missed it.
Cowboy, you're never going to go wrong using Aviation oil in an aviation engine. It's what the manufacturers call for. The ashless dispersent is what used to be called detergent oil.

In the old days they used to use high grade mineral oil. Then they started adding additives. The first additives incorporated in straight mineral piston engine oils were based on the metallic salts of barium and calcium. In highly-rated engines the performance of these oils with respect to oxidation and thermal stability was excellent, but the combustion chambers of the majority of engines could not tolerate the presence of the ash deposits derived from these metal containing additives.

Anyway, if you're getting oil in your cylinder you need to check your valve guides or piston rings. No matter what oil you use, you are going to get some oil in there. That's where the carbon build up is. The slicker Aeroshell Plus will go places no oil has gone before, but it lubricates like no oil before. Lycoming made it happen because they had a problem with the camshaft lobes gualing due to lack of lubrication on the O-320H2AD. Their fix was an additive that is called a semi-synthetic added to the oil. It works, so, why not use it.

I'm still going to use Aeroshell in my planes and Valvoline in my airboat. That's just my opinion and I want others to use the oil they think is best for their engines. Again, you can't go wrong with Aeroshell or any of the other approved aviation oils. A lot of guys swear by Shells aviation oil at my aero club.
Royal Purple, it has a 400% higher shear strength than any oil on the market. This stuff is tuff you can't kill it. Plus you get greatly extended oil change intervals. The aviation community uses it alot and most refinery's and chemical plants use it in their rotating equipment.


Clarification, the avation guys I know who are using royal purple are running auto engines in restoration jobs like 12 cylinder jag's in vintage aircraft, not to sure about true aviation engines but I will call Royal Purple for aircraft info and post it.
Personaly i don't see the point in running Valvoline in place of Av-oil. Theres no price differnce! Matter of fact until a few months ago i was getting Av-oil for a buck a quart less than what 50 or 60 wt Valvoline sells for.

Just my 2cents, Kevin
I wish Aeroshell 100 was that cheap in Highlands County. I haven't found it under $3.44 a quart!!