I don't think that 30wt is your problem. I have always used 30wt in my OD.
In fact, right now I am using 30wt non-detergent oil, with no problems.
Anyway, 20W50 is NOT heavier than 30wt, so the argument doesn't hold up.
20W50 contains polymer additives that make it ACT like 50wt, until the
molecules break down over time, at which point it acts more like 20wt. So,
based on how often people change their tranny oil (not very often, in most
cases), I would actually expect the problem of "too light" oil (if it
exists) to crop up with 20W50, not 30wt.
Remember, the tranny runs a lot cooler than the engine, so thermal viscosity
loss is not much of a factor. Also, consider that in the engine, oil
functions mainly as a thin film lubricant. In the tranny itself, it
functions mainly as a splash lubricant. But in the OD, it functions as
hydraulic fluid. For this reason, I think it makes sense to use a single
weight oil with a "natural" fixed viscosity, rather than a multi-weight oil
that relies on additive packs for its viscosity, and that does not
necessarily react in a linear fashion to changes in temperature and
pressure. But if 20W50 is working for someone, I'm not saying they should
change it.
Detergent vs. non-detergent doesn't really seem to be critical. It is really
just that the detergents are unnecessary in the tranny, not that they are
particularly deleterious.
Anyway, what I'm getting at is that I suspect your problem is not related to
oil type. It may well be related to oil level, though -- have you checked
that lately? If your car was not completely level when you changed oil, you
could easily be down a pint or so. Or maybe you recently developed a leak.
--
Max Heim
'66 MGB GHN3L76149
If you're near Mountain View, CA,
it's the primer red one with chrome wires
on 4/12/05 3:05 PM, Phil Bates at jello@ida.net wrote:
> About a week ago people wanted to discuss the issues with my overdrive.
> At the time, I needed the car for my daily driver, and didn't have time to
> diagnose/correct the half working overdrive situation. Well, my other
> daily driver is now back on the road, and I can work on the overdrive.
> One of the topics that came up was the oil - so here's what I've
> heard/done, and where I have questions -
>
> When I converted the car to overdrive, I used 20W50, and that was the
> recommended oil from the mechanic that initially installed this for me. I
> did a lot of reading, and quickly determined that I was not supposed to
> use a detergent oil. I couldn't find any non-detergent 20W50, so I
> converted to the heaviest (non-gear oil) non-detergent oil I could find,
> which was straight 30 weight. I understand the overdrive system and how
> it engages pretty well, and it makes sense to me that 30 weight is not
> heavy enough to keep the overdrive engaged well - especially if there are
> any iffy o-rings.
>
> So, should I put in detergent oil (like 20W50), or what is the
> recommendation there??
>
> Phil Bates
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