toomanytoys wrote:GL5 only oil seems to have the nasty additives.. GL4/5 generally seems to not, from what information I gathered...
Well technically they both have 'the nasty additives' it's just that original GL5 spec oils have much more of them.
GL5 spec was designed for EP (extreme pressure) hypoid gears. This type of application requires additional shear strength so MORE of these sulphur based additives were used.
The actual problem is rare and only occurs at high temperatures as a chemical reaction between the sulphur based additives and yellow metal components such as brass/copper and phosphur bronze.
Early GL5 products were only tested to meet GL5 specs as it was thought they met and exceeded GL4 specs, Nobody thought of actually putting them through the GL4 testing regime until reports started filtering through about yellow metal damage.
My take on this....and I have spoken to several manufacturers help desks, is that it is only advisable to use GL4 spec OR GL4/GL5 oils, as these have been tested to meet both requirements and presumably have been formulated to meet the GL5 spec with alternative additives (this is my assumption and not fact I'm afraid, nobody was able to give me a definitive answer on this one)
Changing the oil for even the wrong stuff (GL5) is better than not changing it at all.....(of course,don't.. but you get my drift)