No GL4 and 5 are not compatible. Do not use GL5 in a gearbox with yellow metals unless it states in on the product, further, synchromesh is a very light and proven fluid. I said nothing about 90.
Advise me on a GL-4 gear oil
- Thread starter Lubener
- Start date
I made a mistake. I listed the Manual transmission and transmissionaxle gear lube twice. What I meant to say was "It might be in the front diff too but I can't remember if I went with that or the AMSOIL 75W-90 Long Life 100% Synthetic Gear Lube."
Yeah - this is the GL-5 and MT-1 types that also work in GL-4 at a pinch. They get called GL4+, GL5.1 and so on.
All thanks to buffered sulfur additives in modern GL5 formulations that makes them yellow metal safe.
This one for example - https://www.mobil.com/en-hk/commercial-vehicle-lube/pds/gl-xx-mobilube-1-shc-75w90
Who cares about hong kong? Global?
Typical over the shelf GL5 is not good for this application, and any info contrary is misdirection.
I just picked the first one I could find. You’ll get much the same Mobil in any US auto parts store as well.
GL5-MT1 is fairly typical of what you’ll get in any auto store as gl4 compatible now, other than really old stocks of actual gl4 or boutique manufacturers.
obviously not
I mean, there’s got to be a reason why GL-4 has a different name than GL-5, right, and it doesn’t say “backwards compatible” with lower numbers for a reason?
Yes. The logic is apparently that the additive (buffered / deactivated / non reactive sulfur) in GL5/MT1 has changed so that it is "technically" safe for synchromesh. It is sold as such - not that I've ever bought it for an older manual.I mean, there’s got to be a reason why GL-4 has a different name than GL-5, right, and it doesn’t say “backwards compatible” with lower numbers for a reason?
Elkins45
Site Donor 2026
For what it’s worth the owner’s manuals for both my 2007 Corolla and 2009 Scion xB both specified GL-4 or GL-5 gear oils for manual transmissions. I know I used plain old Valvoline GL-5 75w-90 in both my 2003 Matrix and 2007 Corolla and went many thousands of miles afterward with no transmission problems whatsoever.
Toyota has been GL5 in MTs since days of old. I run MTG 75W-90 on my 2019 Tacoma it shifts perfectly
How about differentials? My ford (ranger variant with a suv body) asks for 75w90 GL4 - I have so far resisted the temptation to pour any GL5 variant in here even if I've been the one pointing out the additives in modern GL5 should make it reasonable for use in an environment that requires GL4.
what year model?
Is there something very unique about these diffs that can’t handle yellow metal safe GL5?
It is a 2018 with the 3.2 duratorq aka powerstroke L5 diesel. I tried a yellow metal safe once, briefly - wasn't impressed with the performance (some slippage that I was probably imagining, I dunno. Very minor / early). Drained and moved back to the OEM ford fluid which is still GL4.
Limited slip type differential is different issue
It's like the two issues are being mixed. If for a design GL-4 with lower additives is specified, no don't use GL-5. Nothing to do with brass/bronze/copper
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Oh yes, put GL5 in a transmission with yellow metal synchos, wait a bit, and the difference will be very evident.....I mean, there’s got to be a reason why GL-4 has a different name than GL-5, right, and it doesn’t say “backwards compatible” with lower numbers for a reason?
https://fubex.net/blog/gl‑4-vs-gl‑5-gear-oils/
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