Stuart :
I basically agree, but have a few comments :
The GL-5 specification appears to be tougher in almost all categories than
the GL-4 specification (including copper corrosion), so I believe that
most, if not all, GL-5 oils actually meet the GL-4 specification. Those
that don't advertise that fact may not because :
a) the test is expensive and pointless,
b) They know their oil is too corrosive for typical transmission use even
though it meets GL-4,
c) Apparently some of the original GL-4 tests can no longer be made,
because the required equipment is no longer produced. (Information found at
http://www.lubrizol.com/referencelibrary/readyreference/15-gears/gearper
f.htm )
I even found a comment that GL-4 is "Equivalent to obsolete MIL-L-2105
specification; usually satisfied with 50% GL-5 additive level", which
implies even GL-4 only oils now use the same additive as GL-5, just less of
it.
Also, Redline makes several different gear oils, including "Manual
Transmission Lube" or MTL, which is specifically a GL-4 replacement. It
supposedly provides better synchro action (faster shifts) than their GL-5
oils.
I checked at several local parts chains (Pep Boys, Kragen, AutoZone), all
of them carried GL-4 (only) as well as GL-5 oil. Most of them also had a
Sta-Lube product that is labeled GL-4/GL-5.
Both GL-4 and GL-5 specify the corrosion test be run at 250 degrees F. I
don't know where the 200 degree figure came from. The GL-4 test runs for 1
hour, the GL-5 test for 3 hours. At the end, the finish of a test copper
strip is compared to a standard. Unfortunately, the standard numbers are
different (3b vs 3), and I don't have access to them for a first hand
comparison. However, based on the information that higher numbers
represent higher levels of corrosion, I assume that 3b is worse than 3.
Unfortunately, I have to take this to mean that the reported synchro ring
corrosion means neither of these tests is stringent enough to prevent it.
Randall
On Tuesday, April 06, 1999 10:42 AM, Stuart Steele
[SMTP:ssteele@switchsolutions.com] wrote:
>
> Hello List:
>
> My understanding of the GL gear oil specification on the point of
> GL-4/GL-5 interchangeability is that the oils formulated to meet the
> GL-5 specification may have ( potentially ) higher sulfur levels because
> of enhanced extreme pressure ( EP )additives. The issue with sulfur
> compounds in the oil is that they can decompose under high temperature,
> and reform as corrosive compounds, most notably, sulfuric acid.
> However, apparently the concentration of the acid is such that it does
> not materially put anything at risk except for copper and cuprous
> alloys. Lubrizol has a nice webpage with some good information on
> lubricants at: http://www.lubrizol.com/referencelibrary/lubtheory ;
> further, I have been led to believe that Redline oils (
> http://www.redlineoil.com/unknown ) do not require ( or at least, not
> nearly so much of ) the sulfur-based EP additives, owing to their
> synthetic base stock, so the GL-5 Redline oils are non-corrosive up to
> much higher temperatures than conventional GL-5 oils ( claimed 300
> degrees Fahrenheit/149 degrees Celsius as opposed to the claimed 200
> degrees F./ 93 degrees C. level of conventional GL-5 oils. )
>
> > I had a quick change
> > place insist that they could not be interchanged.
>
> There is some concern about using the GL-5 in an earlier gearbox, if it
> has any copper, brass, or bronze components. I think, however, that if
> you use a GL-4/GL-5, rather than a straight GL-5, then you will be okay,
> as such an oil will meet both specs. I truth, I think that if one were
> to use the GL-5 only spec oil in a susceptible gearbox, and change it
> more frequently than once-every-never ( say, every two years ), one
> would likely be okay, too.
>
> Stuart Steele
|