My two devaluated peso cents. Down here the Fox oil is harder to find than actual gold, so I resorted to use the 15W40 Elf semisynthetic remaining from the oil change of my Reanult Kangoo. Have been doing the same for almost a year now, with good results both on cold (2-3 celsius) and hot weather (37-38 celsius).
Great minds think alike...
Prepare to add a couple of training wheels to the sides of the Kangoo. It's pretty easy to drive It near the tumbling point when taking a turn too fastGreat minds think alike...
Funnily enough I've been dropping the same 15w40 in my Renault (rs172) as well, it positively hates it and hates me for putting it in there since factory spec is 5w40 and cold seasons are better on 0w40. Always had dreams of dropping the F4R engine in a Kangoo.
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It's purpose is purely for reducing friction on the alloy stanchion / polymer bushing interface. It's also very tacky and it's possible Fox have concerns about it clogging EQ valves or something like that in the air spring. For reference I've also heard some service centers don't use it on smaller air forks (for lower lube oil) as it has a tendency to migrate into the dampers and air chambers. I've personally found it good on my 40 and 36 but both are converted to coil and have larger volume than smaller 32/34 forks.
None of the oils I've suggested here are technically pure mineral anyway, and "synthetic" can mean a whole bunch of things from Group III hydrocracked mineral oils to Group IV/V PAO and ester oils. In all cases it refers only to the base oil. Both motor oils and suspension fluids are much more than just a base oil - the actual sliding performance tends to have more to do with the additive package, particularly in the application of an anodized tube sliding linearly in a teflon/polymer coated bushing. This application is quite different to both a combustion engine and a suspension damper.
Re: Fox vs RS. I concur. For Marzocchi and RS products I normally use Motorex oils, pretty easy to find here in Argentina. Since Fox started marketing the 20wt stuff (and I got a Fox fork) I started using the Elf stuff in It.
May I ask what year and model your converted 36 is? I run a Frankensix myself and am considering converting it into a Vanilla too. It was born a 2006 110-150 mm TALAS RC2, became a PUSHed TALAS 36 with new lowers in 2009, a 160 mm FLOAT with steel neg spring in 2013 and recently received a 2015 RC2 cartridge upgrade.
