[Healeys] Diff oil

[Bob Spidell]

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 


-------------------------------- 
Bob Spidell - San Jose, CA 

----- Original Message -----


Thanks Steve and John, 

I'll be changing the oil tonight. 

I really don't want to mix them, but after the DOT 4/5 discussion, it seemed 
like a good question. 

Greg 

--- On Thu, 7/12/12, BJ8 Healeys <sbyers at ec.rr.com> wrote: 

> From: BJ8 Healeys <sbyers at ec.rr.com> 
> Subject: Re: [Healeys] Diff oil 
> To: "'Team Healey List'" <healeys at autox.team.net> 
> Date: Thursday, July 12, 2012, 8:49 AM 
> The way I figure it, mixing 85/140 
> and 80/90 will give you 82.5W - 115. 
> 
> 80W-90 is appropriate for the Healey diff, and all I've ever 
> used is Castrol 
> Hypoy C. 
> 
> Steve Byers 
> HBJ8L/36666 
> BJ8 Registry 
> Havelock, NC USA