Diff Oil.

[Chief]

I just wanted to check that EP80W-90 1L GL4 is the oil for the diff, pretty sure this is what I put in before it all leaked out over time (was under the car tightening the plug earlier) but figured I'd check before buying a new litre, Thanks

[KeithL]

I've got Castrol Diff EPX 80W-90 GL4 in mine which sounds like much the same stuff.

[Chief]

Thanks

[svenedin]

Yes. GL4. You can also use some GL5 oils but only if the bottle specifically states “yellow metal safe”

Stephen

[philthehill]

Personally I would not go anywhere near a GL5 oil.

[Chief]

New bottle arriving tomorrow, and I guess the silver lining is that I won't need to drain the old oil into a container

[geoberni]

Almost a year has passed since this Topic started, but I thought I'd add some info.

I've never really looked into what the difference was between GL4 and GL5.
Just what makes GL5 unsuitable, or less than optimal, for older gearing?

I found an explanation here:
https://penriteoil.com.au/knowledge-cen ... -oils/1036

The actual difference being (note American spelling of sulphur on the Aussie website ):

In normal operation, the sulfur/phosphorous additive forms a black sacrificial coating on the gears and anything it touches with a little pressure and temperature. As the gears turn, instead of wearing, the sacrificial coating of additives is peeled off or worn off. This is normal and acceptable in all steel gears. But when one or more of the surfaces is brass or another soft metal, the sacrificial coating is stronger than the base metal, and instead of just peeling off, it takes with it a few microns of the softer metal.

An API GL-4 gear oil of any given viscosity has about ½ of the level of sulfur/phosphorous additive that would be in the API GL-5 product, so the bond with the metal surface inside the transmission is not as strong, and therefore can be peeled off without peeling a layer of soft metal. This means that the GL-4 product provides a little less extreme pressure protection than a GL-5 oil but less wear on synchromesh components of a transmission. When a GL-5 oil is used in a transmission with synchromesh it can create up to 4 times the amount of copper in a used oil analysis as that of a GL-4 product. Synchronisers will eventually wear to the point where they become ineffective.

[svenedin]

Almost a year has passed since this Topic started, but I thought I'd add some info.

I've never really looked into what the difference was between GL4 and GL5.
Just what makes GL5 unsuitable, or less than optimal, for older gearing?

I found an explanation here:
https://penriteoil.com.au/knowledge-cen ... -oils/1036

The actual difference being (note American spelling of sulphur on the Aussie website ):

In normal operation, the sulfur/phosphorous additive forms a black sacrificial coating on the gears and anything it touches with a little pressure and temperature. As the gears turn, instead of wearing, the sacrificial coating of additives is peeled off or worn off. This is normal and acceptable in all steel gears. But when one or more of the surfaces is brass or another soft metal, the sacrificial coating is stronger than the base metal, and instead of just peeling off, it takes with it a few microns of the softer metal.

An API GL-4 gear oil of any given viscosity has about ½ of the level of sulfur/phosphorous additive that would be in the API GL-5 product, so the bond with the metal surface inside the transmission is not as strong, and therefore can be peeled off without peeling a layer of soft metal. This means that the GL-4 product provides a little less extreme pressure protection than a GL-5 oil but less wear on synchromesh components of a transmission. When a GL-5 oil is used in a transmission with synchromesh it can create up to 4 times the amount of copper in a used oil analysis as that of a GL-4 product. Synchronisers will eventually wear to the point where they become ineffective.

Very interesting Berni, thank you.

It begs the question: how can a GL5 oil be called "yellow metal safe"?

For instance, this oil (which I use) that specifically states: "suitable in transmissions with brass and bronze components"https://www.millersoils-shop.co.uk/clas ... -ep-90-gl5

Stephen