Peter wrote:
Shell 15W50 eats engine seals.
It hasn’t eaten ours.
To be honest there are an awful lot of old wives’ tales about oil, none of them with any kind of rigorous research behind them (and the plural of “anecdote” is not “data”)
I think there is little evidence for saying the W15/W50 eats engine seals, I had quite an old O-360 that finally had to come apart due to crankcase fretting, the old seals had never given problems and showed no evidence of being about to do so.
See the previous threads.
15X50 is obviously not going to just eat your seals, but it degrades them, and a leaking front crank seal is not an exactly uncommon event, uses massive amounts of oil without the culprit being necessarily obvious (due to slipstream blowing it away) and is a real hassle to fix.
Ed’s suggestion, for those who want multigrade (basically IMHO anyone in N Europe whose “50hr” service internal spans warm and cold wx, so no opportunity to change between say W80 and W100) is to dilute the 15W50 by going 50/50.
I have been doing that for a few years and everything is great (with Camguard reducing the oil analysis nicely, as per previous threads).
Colin wrote:
That’s great until you hit a prolonged maintenance problem and the plane is on the ground for a long period and then there is nothing you can do. The joys of aviation.
You could try building a dehumidifier. 
There is a thread about it. PS: And obviously remove the contaminated oil and replace it with something more suitable for storage.
Do they mix well ?
Yes, totally fine to mix any normal aviation oil.
Alioth wrote:
(and the plural of “anecdote” is not “data”)
Excellent…I will use that…
Btw, for our European readers, that can be taken as a really nasty patronising phrase in the UK 
Along with “which part of ‘yellow jackets mandatory’ do you not understand?” and similar forms used by pompous adults when talking to children.
Peter wrote:
15X50 is obviously not going to just eat your seals, but it degrades them, and a leaking front crank seal is not an exactly uncommon event, uses massive amounts of oil without the culprit being necessarily obvious (due to slipstream blowing it away) and is a real hassle to fix.
Well, despite our diet of Aeroshell, I added the first quart of oil to our engine (an O-320-B3B) since the last oil change, 20 hours ago. Which I don’t think is bad oil consumption!
Alioth.
I agree with you my Cessna 152’s require one USQ at about 25 hours. The oil policy is to consider 5.5 USQ to be full ( 6 is full on the stick ) and to add one full bottle of oil when the level reaches 4.5 USQ. We have seen very little difference between Aeroshell multi grade and W80 + in terms of consumption.
