Multi-viscosity vs. single weight oil

[Robster]

My mechanic and I have recently been discussing the pro's and con's of multi-viscosity (semi-synthetic) oil. I've been using Exxon Elite 20-50 for the last 4 oil changes. The mechanic states that single-weight oil is actually a better lubricant than the Exxon Elite because it has less additives (and more oil) and that the singe-weight will "cling" to internal parts longer, preventing corrosion better as well as providing lubrication at start up. I say that the Elite will "cling" just as well to internal parts and that the additive package is superior to the single-weight oil, which results in better overall engine longevity.

Anyone care to jump into this discussion with an opinion or some facts?

 

[OiledMustangGT]

the xw-yy is going to be able to flow better upon initial startup till the engine warms up, the single wieght oil is going to be too thick upon initil startup to flow well enough

 

[cryptokid]

how do you know that mustang? he did not even say what type of engine he is talking about, the mileage, engines condition and etc.

 

[Jimbo]

General aviation is extremely conservative about powerplant technology. No one I know "trusts" multigrade oil in their aircraft engines. Aeroshell W100 and the "+" version is
the only thing I see here in Soutlhern California.

Here is my take on it.

In the case of mineral multigrades, your mechanic is correct in that the polymer VII needed do not lubricate and take up volume in the oil. That is the reason to add synthetic base oils, to reduce or eliminate the need for VII. PAO is a great lubricant, so your mechanic is misinformed on this point.

The properties that allow cold flow also allow more oil to drain off the parts after the engine is shut down. Corrosion may be an issue on infrequently operated aircraft, sInce aviation oils lack the robust additives in road vehicle motor oils. Your mechaninc may be correct here, if you fly infrequently.

Aircooled aircraft engines have large cold clearances compared to automotive engines. A thick oil when cold "fills the gaps" and then thins out when hot as the parts expand. Switching a worn engine to multigrades has resulted in a considerable increase in oil consuption in some cases. Trying to use the same cold flow vs startup wear argument with these engines does not hold true as for automotive. We do not apply takeoff power until oil temperature is in the normal range.

What kind of airplane and engine do you have?

 

[MolaKule]

The PAO in semi-synthetics or partial-synthetic straight weights would act as VI improvers by themselves and extend the weight/grade range.

With modern additive technologies, I can't see an oil film completely draining from parts nor should there be any rust in an engine. The bulk of the oil may be in the sump, but a thin film of oil should persist on the parts, protecting them from dry start-ups and rust, metal deactivation, etc.

 

[Robster]

The aircraft is a Partenavia P-68 light-twin engine; the engines are Lycoming IO-360-200s (200 HP)and have about 1100 hrs. on them; this aircraft flys about 350-400 hrs. per year. I recently switched from Aeroshell 15-50 to Exxon's new Elite 20-50. The Elite is purported to reduce the incidence of valve-sticking, oil consumption, and corrosion. It is a multi-grade semi-synthetic blend with a pretty strong detergent additive. I've noted that since switching to the Exxon, oil-consumption has decreased, and the mechanics have reported a cleaner-than-normal engine interior (valve covers, prop hubs etc.). This aircraft is flown frequently, so corrosion isn't really a factor.

Thanks for the replies. . .my mechanic and I are going to do our own experiment to settle our argument. We're going to soak some engine parts in various oils and expose them to the elements and observe the corrosion. I'll let you know how it turns out.

Rob

 

[USAFREOD]

Robster - Aviation Consumer did a very similar test a couple years ago when Elite first came onto the market (you may want to search back issues if you have available.) They used steel wool as the test specimen, however, and had several controls. The purpose of the experiment was to exclusively look for time to first signs of corrosion. Elite did the best and Aeroshell 15W-50 did next best. The straight weight minerals did worst. Period. The difference was quite staggering. For infrequently run motors like airplane engines, this is something to consider. I know Ag pilots that swear by straight weight mineral, but they run their motors hard almost every day, and change oil frequently... Different use pattern.

HOWEVER, further testing of Elite brought some questions about their additive packages after use in a REAL motor. I ran Elite 20W-50 in my motor for a few oil changes, and started getting bad wear numbers from my UOA. I since went back to Aeroshell 15W-50 (among other things), and my numbers went back down. I am running an O-360-A4K about 150 hours/year.

Just got back from OSH, and spoke with the ASL CamGuard reps. Their additive (I tried it once, and my UOA did in fact improve) is basically a Ca detergent with another Boron additive. Cleaning the motor from the inside really does appear to work. They have more data points from use on piston helos.

You MAY want to consider LC. I have "heard" that it works well in air-cooled motors as well. I have "heard" that UOAs are good, and basically cleans the motor well.

Mid to high-time Lycs have an issue with cam spalling. During one of the motor forums at OSH, it was emphasized you do not even want to do an engine run up without warming the oil well into the Green Arc. For some reason, unless you have had your case modified at last OH, it is very hard for the motor to get oil up where it is needed most (cam and valve stems) for Lycs. Bill Scott from Precision Engine has a long diatribe on his website about this. Bottom line, at startup I would be less worried about oil in the cylinder barrels than at the top of the motor. The better the "residual coating" on the top end, it appears the better for your motor.

BUT, you run your motors far more than "average". MOST sole owners run their motors about 100 hours/year. I run mine closer to 150. This is very infrequent. You stated 350 - 400/year. This motor really is NOT a candidate for the corrosion related issues the rest of us see...

Oh, and valves will stick with straight weight oils as well. Itis more a function of all the ****ed lead and stabilizers in AvGas than the lube. That's why there is still a huge market for TCP (lead scavenger) in the piston market.

If you get a chance someday, take a trip to AirVenture and spend some time in the engine forums. I learned a **** of a lot this year. You can even participate in a complete tear-down of an O-360 if you want...