Gear oil
11-17-2011, 10:38 AM
#16
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Of course is synthetic! It's BLUE!! I know it doesn't have as much horsepower as purple 
but I also want protection because this is a street car.
...Just kidding, I don't know for certain but I would assume if it was synthetic it would be written all over the bottle, which it isn't.
but I also want protection because this is a street car. ...Just kidding, I don't know for certain but I would assume if it was synthetic it would be written all over the bottle, which it isn't.
11-17-2011, 02:15 PM
#19
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A couple month ago I switch to Red Line All-Synthetic 75w90 NS GL5 in my 968 & I'm very satisfy.Shifting is smooth like butter in all gears even in cold weather up here.BTW that is what was recommended in my owner manual.In my ex 944 NA I use Castrol Syntec 75W90 GL4 for over 12 years & never had any problems the car is still going strong & shift beautifully.What I'm trying to say is,if the tranny has synchros issues no matter what you put in there it want solve the problems migth help a little but it won't fixe it.
11-17-2011, 03:18 PM
#20
Race Car
Yes earnie. My 87 924S is recommended for GL-4 (sae 80!) as is most, if not all, 5 speed cars. The 968 is prescribed GL-5. The difference lies in the syncros, specifically the material they are made out of. The way I understand it is that GL5 is ideal for the differential, and GL4 is for gearboxes. As both share the oil in our trans, Porsche opted for GL4 as GL5 does not lend itself to smooth shifting...that is until the 968. GL4 is actually a more stringent rating than GL5. To be more technical, one of the biggest differences is the ph (acid) level in the oil. GL5 is not compatible with the bronze synchros used in early cars and accelerates wear in areas, also this reaction breaks down the oil prematurely and wear is further accelerated.
This discussion is hot amongst the 911 and aircooled VW guys as their gearboxes need GL4 which is getting harder to find. Amsoil is considered one of the best and is readily available in my area...it was my choice. I don't want to start an argument on this subject as I know plenty of people who run GL5 in various Porsches with no adverse effects including myself. I've run GL5 for years but changed it often. I demanded GL4 after I learned a few things.
This discussion is hot amongst the 911 and aircooled VW guys as their gearboxes need GL4 which is getting harder to find. Amsoil is considered one of the best and is readily available in my area...it was my choice. I don't want to start an argument on this subject as I know plenty of people who run GL5 in various Porsches with no adverse effects including myself. I've run GL5 for years but changed it often. I demanded GL4 after I learned a few things.
