Jump to content

Hypoid oil


Recommended Posts

EP80/90 GL4 is fine to use in a diff.


The most important bit is GL4.


Some, but not all GL5 spec oils will damage the diff.

The oil suppliers are not always very open about the formulation of their oil, so it can be difficult to establish if any particular GL5 spec oil is "yellow metal" safe.

It's easier to just avoid GL5 spec oils - just in case the one you happen to use is not yellow metal safe.


By the way, you can use a GL5 spec oil to oil your trunions - the problem ingredient only becomes a problem when the oil is hot and under a lot of  shear pressure, which is only found in the diff.

Link to comment
Share on other sites

If Halfords have been recommending this one to you, I have been using it for years without problems:




Proper EP90 GL4 is also available from Canley Classics. As Kevin says, GL5 is only an issue when in the challenging environment of a diff or gearbox, when it comes under extreme pressure and gets flipping hot. Some formulations apparently attack phosphor-bronze and other "yellow metal" components found in these assemblies under those conditions.


On a point of information, where engine oil is concerned  I read somewhere that Halfords Classic 20w50 is an identical formulation to the original Castrol GTX, but I am sure someone out there will correct me if this is wrong. For myself, I have tended to steer clear of synthetic engine oils, although I know John Kipping swore by Mobil 1!




Steve C

Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now

  • Create New...