I swear, this is the last time I will write about this subject. Last night I
checked the handbook that came with my '68 GT when I bought it new, the
handbook being the only part of the car to have survived a sudden T-bone
encounter with a Pontiac in '78. In it is a list of recommended oils by brand
name and weight, grouping the engine and tranny in the same column. In short,
we're both right, which means I'm more wrong in saying that single-weight was
preferred for the tranny. It specifies both multi-grade and straight 40W for
temperate climates, which covers most of us. Some brands it favored 10W40,
others 20W50, some 10W30. Maybe that was all that was available in those
brands. But what struck me was that for the single-weight oil it tended to
favor 40W. I used 30W when the car was new, but then again I was in Savannah
at the time, and the heat may have made me go thinner.
Jay Donoghue
72B-GT
66 Mustang
In a message dated 11/7/2003 5:24:28 PM Eastern Standard Time, ccrobins@ktc.com
writes:
> Well, my Bentley manual also contains the driver's handbook for '62 -
> '70. It was published and copyrighted in '69. It contains a chart in
> it that mainly calls for multi-vis oil in the engine & gearbox, if you
> can get it. Base viscosities vary as a function of ambien temps. It's
> kind of amusing, really. It actually recommends various oils by brand
> name. They wouldn't dare do that these days, huh? But the point is
> that even way back in '69 they were using multi-vis oil. They didn't
> change it 10 yrs later as you imply. Also, some of those recommended by
> brand - say Mobil Special 20W-40 - must have been detergent oil. Anyway
> it doesn't specify non-detergent.
>
> Do you suppose the 5W was too thin for your OD because of wear?
> That's what I suspect.
>
> Here's something interesting that I didn't notice before in the
> chart. Where the vis is specified for the carb dampers, 10W something.
> So my 20W-50 isn't right for that app. Grr, hoist by my own petard! (G)
>
> Cheers,
>
> CR
>
> ATWEDITOR@aol.com wrote:
> > In a message dated 11/7/2003 1:50:30 PM Eastern Standard Time,
>ccrobins@ktc.com writes:
> >
> >
> >> What I don't understand is why you don't believe that the guys who
> >>designed and built the gearboxes/overdrives didn't know
> >>what oil was
> >>best to use in them.
> >
> >
> > Well, since I was the owner in 1968 of a brand new '68 GT with the same
>gearbox and overdrive
> as the later years and my memory isn't completely in the dumper I can
> recall exactly what
> they guys who designed and built the tranny called for and it was 30W,
> period. I believe
> it was non-detergent, too, but I'm less clear about that part. Oh, and
> I drove that for 10
> years with no problems EXCEPT when, later in its life, I briefly went
> to 5W50 oil and the darn thing refused to stay in OD.
> > Now, maybe the later geniuses who drove the British motorcar industry into
>the ground decided to recommend multi-grade did the correct research to back
>up that change, but I'll go with, as you said, what the guys who designed and
>built it
> recommended.
> >
> > Jay Donoghue
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