[Healeys] Diff oil

[Richard Collins]

Also applies to brake fluid as well...I do DE's with a car (not the Healey)
and use high temp DOT4 brake fluid (currently Wilwood). if fluid of different
temp ranges are mixed, it takes on the characteristic of the lower
temperature. I do not use silicon brake fluid on any of my cars but do change
it regularly, aided by a brake fluid moisture meter Richard of KYBN7 #440
 > Date: Thu, 12 Jul 2012 19:05:09 +0000
> From: bspidell at comcast.net
> To: gmandas at yahoo.com
> CC: healeys at autox.team.net
> Subject: Re: [Healeys] Diff oil
>
> Everything I've seen/read/heard indicates you shouldn't mix oils of
differing viscosities, esp. multi-vis oils. The multi-vis oils are a blend of
base stock--e.g. 10W-40 has a base stock vis of 8 (I think)--and various
'viscosity improvers' or VIs. The VIs are polymers that start out as straight
chains then sort of 'coil up' as they get hot to thicken the base stock beyond
what it would otherwise be at a given temperature. I don't believe the effect
is linear--i.e. mixing 80W-90 and 85W-140 won't give a blend proportional to
the mixed quantities. Some say you shouldn't even mix different brands of same
viscosity, but I personally wouldn't lose too much sleep over that. As an
aside, you can mix grades of gasoline to get differing octane ratings; in
fact, I believe most gas stations have just two tanks from which a third blend
can be mixed at the pumps.
>
> I don't think 85W-140 would hurt a Healey diff--it may even be recommended
in the manual, haven't looked in a while--it'll likely be a similar base stock
to 80W-90 with tons of VIs. The problem is the VIs chains shear over time and
the higher vis number goes down.
>
> Bob