Can MT oil be both GL4 and GL5?
06-24-2003 | 10:57 AM
#1
Thread Starter
Member
Joined: Nov 2002
Posts: 237
From: Hyde Park, NY
Can MT oil be both GL4 and GL5?
I want to change the oil in my 99 5speed, and I see a lot of discussion about NOT using GL5. The owners manual does call for GL4 80W90. I can only find oil locally that is either GL5/MT1, or some that say both GL4 and GL5. Do you think it is safe to use the oil that says it is for both GL4 and GL5? I can not find anything that says only GL4.... 
06-24-2003 | 11:30 AM
#2
I don't understand how an oil can be compatible with GL4 and GL5 specs. A tranny fluid that is straight GL5 contains stuff that's corrosive to certain metals in the tranny. GL4 in contrast does not. Red Line's website under tranny fluid gives a pretty good explanation of the issues at hand. Here it is:
Maybe someone else can comment?
GEAR AND SYNCHRONIZER WEAR PROTECTION
Most manufacturers of manual transmissions and transaxles recommend an 80W or 90W GL-4 lubricant. GL-5 gears oils which are required in hypoid differentials are not used in most synchromesh transmissions because the chemicals used to provide the extreme pressure protection can be corrosive to synchronizers, which are commonly made of brass or bronze. Typically, the use of a GL-5 lubricant in a synchromesh transmission will shorten the synchronizer life by one half. The extreme pressure requirements of spur gears and helical gears found in transmissions are not nearly as great as found in rear-wheel drive differentials. A GL-4 lubricant provides adequate protection for most manual transmissions, unless a unique design consideration requires the extra protection of a GL-5.
Most manufacturers of manual transmissions and transaxles recommend an 80W or 90W GL-4 lubricant. GL-5 gears oils which are required in hypoid differentials are not used in most synchromesh transmissions because the chemicals used to provide the extreme pressure protection can be corrosive to synchronizers, which are commonly made of brass or bronze. Typically, the use of a GL-5 lubricant in a synchromesh transmission will shorten the synchronizer life by one half. The extreme pressure requirements of spur gears and helical gears found in transmissions are not nearly as great as found in rear-wheel drive differentials. A GL-4 lubricant provides adequate protection for most manual transmissions, unless a unique design consideration requires the extra protection of a GL-5.
Maybe someone else can comment?
06-24-2003 | 12:06 PM
#3
Thread Starter
Member
Joined: Nov 2002
Posts: 237
From: Hyde Park, NY
Thanks, that doesn't sound right to me either... I was thinking about the redline MT90 stuff instead of regular oil, does anyone know a good place to buy it online? I don't mind the extra cost if it is good stuff and doesn't damage anything in the long run....
06-24-2003 | 12:09 PM
#4
Senior Member
Joined: Apr 2002
Posts: 590
Re: Can MT oil be both GL4 and GL5?
Originally posted by slfalco
I want to change the oil in my 99 5speed, and I see a lot of discussion about NOT using GL5. The owners manual does call for GL4 80W90. I can only find oil locally that is either GL5/MT1, or some that say both GL4 and GL5. Do you think it is safe to use the oil that says it is for both GL4 and GL5? I can not find anything that says only GL4....
I want to change the oil in my 99 5speed, and I see a lot of discussion about NOT using GL5. The owners manual does call for GL4 80W90. I can only find oil locally that is either GL5/MT1, or some that say both GL4 and GL5. Do you think it is safe to use the oil that says it is for both GL4 and GL5? I can not find anything that says only GL4....
I would, however, just order the correct GL-4 stuff like RedLine MT-90 since you're going to leave it in there a long time. You can order it online if you can't find it locally.
-RMB
06-24-2003 | 12:25 PM
#5
Thread Starter
Member
Joined: Nov 2002
Posts: 237
From: Hyde Park, NY
Thanks, just ordered up 5 qts of redline MT90 from a link I found using the search, which (thank heaven) is working again... I've been using Mobil-1 in the engine since new, so I don't have any problems with synth oils... Now if it would only stop raining here in upstate NY on the weekends, I will get to change it...
03-03-2008 | 05:42 PM
#6
Newbie - Just Registered
Joined: Oct 2005
Posts: 7
hi, had the same problem finding gl4 so the last place i went to today had it. napa auto parts has gl4 specific gear oil. It does not say anything about gl5 on it. It is aproved of use on vehicles requiring gl3 and gl4 gear oil. It is not synthetic but atleast it will not eat away at my syncros.
03-03-2008 | 06:39 PM
#7
hi, had the same problem finding gl4 so the last place i went to today had it. napa auto parts has gl4 specific gear oil. It does not say anything about gl5 on it. It is aproved of use on vehicles requiring gl3 and gl4 gear oil. It is not synthetic but atleast it will not eat away at my syncros.
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