GL-4 vs GL-5

[widman]

Having heard all the explanations about the buffered additives and the other various rumors about not needing GL-4 or that GL-5 replaces it, I've put together something that should kill those rumors and myths for all but the hardest die-hard. I've seen too many worn out synchronizers to just let is slide.

GL-4 vs GL-5

 

[webfors]

I think if a tranny calls for gl4 that's what you should use. You'll see that with most front wheel drive imports with brass synchros, so I agree with you there that gl5 should be avoided even if the bottle states it's backward compatible.

However, if a tranny calls for gl5 you would be crazy to put gl4 in, like in the subaru 5mt.

 

[widman]

Exactly

 

[edhackett]

Widman, have you explored the Chevron Delo ESI 80W-90? While it is rated GL5, it doesn't contain zinc-phosphorus EP additives. It works perfectly in older Alfa Romeo transmissions that specify GL1. It seems to have the perfect friction properties for syncros. The ISOSYN base stock makes for decent low temperature performance too.

Ed

 

[mechtech2]

ed - It's the sulfur that is in question concerning yellow metal corrosion.

 

[Ken2]

How about a GL-5 gear oil that passes the ASTM D-130 copper strip corrosion test with a rating of 1b, or even better, 1a?

The Copper Strip Corrosion Test ASTM D130 is used to evaluate the corrosive tendencies of oils to copper containing materials. In this test, special three-inch copper strips are cleaned, polished and immersed into a test tube containing the oil being evaluated. The test tube is held in a water bath for three hours at 212ºF (100ºC). At the end of the exposure period, the strip is removed and cleaned. The strips are compared to a specially prepared set of standardized reference strips and rated against these standards on a scale of Class 1 (slight tarnish) to Class 4 (heavy tarnish). An industrial gear lubricant that exhibits a 1b classification in this test is considered to exhibit good resistance corrosion to yellow metals.
http://www.machinerylubrication.com/article_detail.asp?articleid=616

 

[edhackett]

Yes, the sulfur. That's what I meant to type. No zinc-sulfur EP additives in the Delo.

Thanks for pointing out my mistake.

Ed

 

[synormin]

widman, Thanks for posting this info, pretty much the info I was after. However Ken2 has a great question...any additional thoughts or stick with GL-4 only where it's specified?

 

[edhackett]

That test is very short term, 3 hours. 30K miles is roughly 800 hours. That test also does not take into account H2SO4 formation from moisture that accumulates due to condensation. It's a good indicator of how an oil might do, but when all is said and done, GL4 will be less corrosive to yellow metals.

Ed

 

[widman]

The point is not the corrosion, it is the wear. The GL-5 DOES pull off brass from the synchronizers. Too many people are hung up on the corrosion thing, which is probably higher in the GL-5, but the issue is wear.

I'm curious myself about the Delo. I like it in the differencial, the time I put it in my 4Runner transmission, I had hard shifting, but I replaced the 80W-90 Delo with 75W-90 GL-4, so I don't know how much effect was by either.

The Delo, with it's borate, will not peel off any brass at all, and can only be corrosive in the presence of water (it is a salt). I know its polar attraction is great in gear boxes, but do not know how well they release in the synchronizer. I should mix up some with the 75W-90 and try it in one of the vehicles where I have GL-4 75W-90, but lets make that a maybe. (I have Borate gear oils in every viscosity from ISO 68 to ISO 680, so mixing isn't a problem. just time.

 

[mechtech2]

I forgot to thank widman for the excellent article he wrote.
I do have a quiestion, though.
When the synchros wear with sulfur in GL4, you state that it is because the one surface is harder, and tears off the brass.
But the offending side is stee], which is harder anyway.
Are we to give all the credit to the layer on the steel, therefore?

 

[widman]

it is the GL-5 that wears it. If you have two mating steel surfaces, the sulfur/phos takes the beating, peeling and bonding until it can't anymore. When you have the brass/steel arrangement, as in most synchronizers (there are exceptions) the steel does not wear, but as it peels the sacrificial surface off the brass, it taks some brass with it. so your steel pieces are normally in excellent shape.

Steel always wins, but with brass, the sulfur/phos coating kills the brass while it loses.