GL4 vs. GL5

Mark W. Byrum, Jr. markbyrum at
Wed Dec 11 18:12:55 EST 2002

[ Picked text/plain from multipart/alternative ]
Many years ago (late 1970's) when seeking the best transmission fluid for a=
 BMW 1602 I had purchased and was refurbishing, the manual called for "non-=
hypoid gear oil" of either 80 or 90 weight (I cannot recall which), but no =
one could tell me why "non-hypoid" was called for; and all the gear oil I c=
ould find on the auto parts shelf was specifically of the "hypoid" variety.=
  My father worked in the parts department for Ford Tractors and advised me=
 that "hypoid" gear oil, at
least as respects Ford Tractor transmissions, degraded the bronze synchro r=
ings, thus Ford stocked and sold a "non-hypoid" gear oil for certain applic=
ations.  I purchased some of that stuff and my transmission and I (as the s=
tory goes) lived happily ever after.  If Audi uses bronze synchro rings in =
certain transmissions and one type of fluid is "hypoid" and the other isn't=
, I would steer away from the "hypoid" type.  I offer that personal insight=
 on the matter.

Louis-Alain Richard wrote:

> Rob,
> If you can find some, Castrol Hypoy IS really mineral GL4 oil.  However, =
my parts store carry only Castrol Hypoy C, which is GL5.  And like you, I d=
id it last summer with the wrong one so I want to switch back to GL4.
> Interestingly, the oil I drained form the car was Dexron ATF (thin, red s=
lippery stuff) like you find in any manual trans GM car!  Somebody probably=
 wanted to ease the gear change and they were right; the trans was really e=
asy but longevity was my primary concern.
> Try this link:
_id=3D15&product_category=3D3 <
> Louis-Alain
> 83 urQ
> Subject: GL4 vs. GL5
> From: qshipaz at
> Greetings Audinauts,
> Hmmm. I heard that GL5 should not be used, but could never remember why. =
Guess the GL5 I topped the TQ box off with last week is gonna come out! Que=
stion, though: I believe in Redline's quality, but I am superstitious about=
 using synthetic in a car which has likely always used "bean oil"- maybe ju=
st for the potential of new leaks developing. But otherwise- where can you =
get non-synth GL4?? I used to use Castrol in my departed 5kt, but I can't l=
ocate the stuff anywhere....
> Regards,
> Rob

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