# Gear oil; GL-4 vs GL-5



## matt1215 (Jul 7, 2004)

What's the difference between GL-4 and GL-5? Big discrepency between what the book says and what most stores have. 

I've been in the habit of changing my gear-oil regularly (15-20k), but I'm no longer near store that stocks 75W-90 GL-4. Recommendations online or in Orange County, CA?


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## Sethticlees (May 30, 2002)

Redline MT90 :thumbup:


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## funkpacket (Feb 13, 2004)

if your by a pepboys they now sell royal purple. If they have any royal purples in stock you should be able to snag some 75w90 gl-4 mtf. Honda people swear by the stuff. BTW, unless gl-4 is stated on the bottle, DO NOT UNDER ANY CIRCUMSTANCES USE GL-5 SPEC MTF. GL-5 spec fluids will destroy the softer metals in nissan trannies. Gl-4 is the only way to go with our cars


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## Bror Jace (Apr 26, 2003)

_"Unless GL-4 is stated on the bottle, DO NOT UNDER ANY CIRCUMSTANCES USE GL-5 SPEC MTF. GL-5 spec fluids will destroy the softer metals in Nissan trannies. GL-4 is the only way to go with our cars."_

This is correct. Many GL-5 gear oils use a sulfur-based additive package which chemically etches itself onto the face of iron/steel gears and acts as an extreme-pressure agent to protect them from more serious wear. However Newer ones (Chevron Delo gear oil) use a non-corrosive boron-based additive package. Good stuff.

That same process actively eats away at soft, yellow metals (copper, brass & bronze). 

Take a whiff. If the 75W-90 (or 80W-90) smells like sulfur, don't use it. Pep Boys sells Coastal gear oils which are dual-rated (GL-5, GL-4 & GL-3) and are safe (and cheap). I believe they use the boron-based additive package as well.

Red Line MT-90 is a 75W-90 GL-4 gear oil and is an excellent choice for anyone looking for a 90 weight gear oil for a transmission. Because it is a true synthetic, it's also better on cold mornings than most other lubricants.

_"If you're by a PepBoys, they now sell Royal Purple. If they have any Royal Purple in stock you should be able to snag some 75W-90 GL-4 MTF. Honda people swear by the stuff."_

Funny, they shouldn't. No Honda that I know calls for a 90 weight gear oil in the transmission. They used to call for 10W-30, now they call for Honda MTF. These are significantly thinner fluids that a 75W-90. Royal Purple Syncromax is a GL-4 fluid ... but it's way too thin ... being as thin as an ATF for standard transmissions calling for that kind of oil. 

Want the very best gear oils? Here's a private blender who makes a couple great synthetic MTFs for Nissans: MTL-P (75W-85) and MTL-R (75W-90). 

http://www.specialtyformulations.com/index_files/Page457.htm 

Both are dual-rated as they protect as well as a GL-5 however are as safe on soft, yellow metals as a GL-4.

I use MTL-P in my SpecV's 6-speed and will use nothing else. It was significantly better than the Red Line MTL/MT-90 mix I had in there previously.


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## funkpacket (Feb 13, 2004)

Bror...do you notice a difference in shift feel/effort in using the specialty formulations blend verses other synthetic mtfs? I have read on the bitog forums about the quality of some of the aftermarket gear oil cocktails but i havent pulled the trigger on buying any yet. Any better than redline?


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## Bror Jace (Apr 26, 2003)

Prior to using _SpecForm's MTL-P_ I used an 80/20 cocktail of Red Line MT-90/MTL. The stuff was OK. Better by far on winter mornings ... but it might not have been as good as the factory fill once the tranny was up to operating temp.

I drained this stuff into a clean pan, then filtered it into a clean gallon jug. It's still around here ... somewhere. I'd give it away to any local guy who contacts me. Heck, I did the same with the factory fluid ... and i still have a quart of that stuff around here somewhere.

But once you use MTL-P, I can't see anyone going back to anything else.

I'd like to see someone make a 12.0-12.5 cSt blend of the 2 Royal Purple syncromesh fluids.


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## matt1215 (Jul 7, 2004)

Thanks. Confirms my suspicion that I committed a grave sin about 4 years ago when I refilled with Mobil-1 GL-5 75W-90. It shifted really, really smooth, right into the gears. I changed-out about 3k later to the first GL-4 I could find when it just didn't feel right, shifting a little too far into the gears. Engine likes M-1, but tranny says 'YUCK!!'.

I think my gearbox has since forgiven me (60k later), I've since kept her supplied with plenty of fresh GL-4. Thank you for suggestions on products :thumbup: Any experience with Penzoil's GL-4 75W-90?


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## Bror Jace (Apr 26, 2003)

*matt1215*: _"Any experience with Penzoil's GL-4 75W-90?"_

Nope, and that's a tad thick for my tranny which calls for 75W-85.

You might try this section of BITOG:

http://theoildrop.server101.com/ubb/ultimatebb.php?ubb=forum;f=16

Do a search.


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