I recently purchased a C185 with a IO-550f, 135hrs smoh. It came with 20-50 in it. Should I stick to the 20-50 in the hot Colorado summers?

Yep

Stick with the Phillips 20-50!

Kurt

I'm going to be the contrarian here. If you want your starter drive to last, 50 wt in the heat is the way to go. It won't shear down like a multi grade can in the heat. Multi grade when it cools off fall and winter. Especially if you don't preheat. Most of the Continetals we see that have starter drive issues have been run on multi grade. The ones that live on straight weight not so much. -YMMV. Do not try this at home. Preformed by complete amateurs in uncontrolled conditions. Etc.

Thanks for the help!

Just to muddy the waters, and because I think different opinions are interesting...

My mechanic swears by straight-weight oil, temperatures permitting. He's very old school, but also a chief mechanic for the FSDO, so it's not like he hasn't been keeping up on recent developments.

On the other hand my former tailwheel instructor swears by multi-weight oil. On the field he is both universally disliked and universally (if begrudgingly) respected for his mechanical knowledge. One person who can't stand him but still went to him with a mechanical problem summed it up this way: "It's like he's some sort of ph...ing Rain Man for engines..."

So with those two opinions foremost in my training, I just mixed the two... 2:1 straight-50 and multi-weight in the summer, then 2:1 multi-weight and straight-50 in the winter. (It never really gets that cold here.)

I was explaining this system to the aforementioned tailwheel instructor and, after thinking about it, he said I had it backwards. His take on it was that multi-weight oil has a higher heat tolerance than straight-weight oil, so I should be running the multi-weight-heavy mixture in the summer, not in the winter. His opinion was that a thermally-compromised oil was a far greater risk than too viscous an oil.

I thought that was an interesting point. Then I found a good price on Phillips 20-50 and bought several cases. I mix it liberally with CamGuard, change it every 25 hours, and didn't think too much about it until just now. I guess if in the future if Aeroshell is available at $20 a case less than Phillips, I'll go back to using that, with the same mix of CamGuard and 25hr oil changes.

Hell, I used to change my oil every 25 hours of Hobbs time, which started when the master switch was flipped. Some of that oil wasn't even brown when it went down the drain. I'm sure there's a true right and wrong oil for any given engine, but I doubt any of us will ever know what it actually is.

Keep it topped off, change it often, match it to the temps you fly in. Past that it probably doesn't matter...a Mandatory Service Bulletin will probably dictate a engine tear down before you reach TBO anyway...

I just got an oil analysis back from a ~25 hr sample. Seemed to have a ton of life left in the oil. My 50 hr sample shows about the same. If it makes you feel better to change it often - go for it. Can't hurt anything!

FWIW, it appears that samples with longer periods of un-use look worse than longer interval samples with frequent use.

I may start a cat fight here but oh well.....

We have not had good luck with Aeroshell 15-50 in our family. Trashed my uncles IO-520 in his 185, engine was low running time, low calendar time in dry environment. 15-50 lubricates well when running, they all do, but it does not adhere well to parts while sitting which exposes parts to rust and or corrosion. Exxon Elite according to Aviation Consumer does best at protecting sitting parts and Phillips is a close second. I have seen cams that have run 15-50 Aeroshell and not flown every day in tough shape, one friend's cam on a 540 Lyc had only 400 hours on it and at teardown for crank AD was discovered to have some ugly deterioration and pitting. This is not a straight weight/multi weight issue, its experience with Aeroshell 15-50. I have ran just about everything over the years with good results except 15-50 Aeroshell. I will no longer put it in any of my engines. YMMV

Kurt

RockHopper wrote:.... Most of the Continetals we see that have starter drive issues have been run on multi grade. The ones that live on straight weight not so much. ....

I have heard this about AEroshell 15/50 semi-synthetic, but not so much about Phillips 20/50.
I've been running XC20/50 in my 470 and the starter grabs ahold just fine.

I think Phillips came up with a "mineral oil" version of it, but
FWIW ECI does (or at least used to) recommend regular XC20/50 for break-in.
But not Aeroshell 15/50 (too slippery).

I can 2nd or 3rd the recommendation for Phillips X/C 20/50. Been running it in my IO-550 for the past 5 years ever since break in, and have had good luck with it. The engine burns almost no oil. Maybe a 1/2 quart ever 10-15 hours. Ran AeroShell 15/50 in the previous engine. Seemed fine, but now I think I like the Phillips better. YMMV.

For conversation, I agree with Kurt about Shell Multigrade. Not so good. Too many torn up motors. Phillips x/c seems to have proved itself. The issue I have witnessed with the multigrade in a high heat condition is viscosity shear out. When you drain your oil and it comes out looking like water, your oil is sheared out. The way multi grade is produced is that the refiner starts with a low viscosity base stock which gives good flow at lower temps. Then an additive package and viscosity modifiers are added to increase viscosity protection as the oil temp increases. Under extreme conditions, the oil eventually starts to shear out and looses it's ability to maintain viscosity. ( example is a heavily loaded float plane on repeated long climb outs in high temps and high density alt) The other issue I've seen is a motor that runs multigrade, but is infrequently flown tends to be quite dry of oil on the rotating parts and cylinder walls after sitting. I have bore scoped engines that have sat for awhile with both multigrade and straight weight. The ones with multigrade apear rather dry as the oil appears to have drained off. The engines running straight weight still seem to have some residual oil sticking to the cam lobes/lifters and cylinder walls. Multigrade does have a place for the frequently flown aircraft in moderate cool climates, but with any chance of heavy use, my money is on the well proven straight weight that will take a beating and go the distance.

I don't have an engine over 400 ci or a Conti, but my oil analyses of Phillips XC and CamGuard seem to indicate it keeps viscosity pretty well in Alabama summer temps. I'm not unhappy with or married to the brand - it's worked good for me so far. I've been watching this thread to see if there's a better option.

I do what my IA recommends, and he recommends straight weight Aeroshell, 100 in the summer and 80 in the winter, with 50 hour oil and filter changes. My O-360 burns very little oil--I will usually add a quart between oil changes, sometimes 2 quarts, so it burns out about 1 quart per 20-25 hours. I don't add oil until it gets down to about 6 1/2 (it holds , so the only time it has 8 is right after an oil change. The engine has around 800 hours on it now.

Cary

May be considered anecdotal, but it was my direct experience. My current plane was purchased with about 600 SMOH. Had been maintained with AeroShell 15-50 synthetic. When I bought it I put about 30 hard hours on it getting back home and noticed high oil consumption (for me). I was adding a quart about every 2 hours. Got it home and it continued that way under all conditions of operations. First oil change came up and I switched to XC 20/50....not due to any pre-odisposition, just had several cases from my last plane.

Dramatic improvement. Now, two years later it's not perfect but I can go on a long trip and only fill a couple of times. Recent trip to Idaho (25 hours) only added 3 quarts. FWIW.

I've owned mostly big contitnals. AeroShell 100w and Phillips cross country have always been no issue for me.

Interesting.

I just got this from the Blackstone Laboratories Newsletter yesterday.

https://gallery.mailchimp.com/f641390cb ... _AC.01.pdf

Interesting article from Blackstone. Seems to confirm that there is really no one oil that's better than the others.

Also anecdotal, but I've never seen any change in oil consumption regardless of what oil I run. Not saying it doesn't happen, but my engine doesn't seem to care. If it did I'd stick with the low consumption variety I guess.

As far as oil "shearing out"... I'm sort of confused. If that's an inherent weakness of multi-weight oil, why does multi-weigh oil have a higher thermal ceiling than straight weight? Or would straight weight oil "shear out" as well under those conditions?

Personally I've never drained oil that behaved that way. I run two oil temp probes: one before the oil cooler and one after. I don't let the pre-cooler oil get over 250 degrees, which puts it at about 180 degrees after it runs through the cooler. That's an exceptionally hot scenario...it normally runs 25 degrees cooler on climb out, and 80 degrees cooler in cruise.

What temperature does oil have to get to in order to "shear out"?

And ya, I'm probably wasting money with 25 hour oil changes, especially when I fly a lot. I guess what I like about that regime is that I don't have to worry if a trip is going to put me a few hours over change times. If my 25 hours goes to 33 hours I don't worry about it...not sure I'd be real happy running to 58 hours, though.

One interesting point that isn't mentioned in the Blackstone article is at what ambient temperature multi-weight oils really come into their own in reducing engine wear. I was always taught that the most damage to an engine happens at start-up due to poor lubrication, so reducing that seems more important than any other single aspect. Yes? No?

My O470K seems to burn less oil with XC20-50 than with W100.
Maybe a quart difference over 30 hours (my oil change interval).