EP140 instead of EP 90 in Differential

[Puddles of Oil]

Does anyone on here run EP140 in their classic car differential? I have a 1965 Sunbeam and was advised that putting EP140 in the back axle instead of the Rootes recommended EP90 was a good idea. The thicker oil apparently helps older axles in some way.

Anyone do it or are there any downsides if I tried it?

[OutInTheShed]

FWIW, I think you can get multigrade EP oil? EP 90W140 or something?

Also, I would think about using a quality synthetic version, assuming it will stay in....

I used to run a Guzzi with expensive oil and Moly additive in the bevel box, but that was a long time ago!

[austina35]

EP140 would be very thick in cold weather. Probably better in a steering box. I'd stick with the EP90.

[hidetheelephants]

Who was advising this? Sounds like a terrible idea, maybe it might quieten a knackered and whiney diff somewhat but other than that it's a bit pointless, stick with the original spec.

[astonman]

140 ( hipress), is by far the best oil for protecting your gears in the diff . Basically,thick oil had hugely protective abilities. Thinner or more modern synthetic oils,which are thinner,will probably give better mpg, because they produce less friction.
However,in terms of gear face protection, viscosity will pretty much always win,and it will likely be quieter,though some clever,low viscosity oil ,like Castrol synthetic diff oil have mega noise suppression!