[Evil C]

Gear and crank oil viscosity measurements use different scales (they're NOT the same scale - gear oil numbers are much higher than crank oil numbers, for the same viscosity). Hence, there's a good chunk of overlap in viscosity between gear and crank oils. It's possible to engineer a 10W40 viscosity within the required range for this oil spec. such that it is also within the required range for MTF-94 gear oil. Then the only difference is the additive package, but this can also presumably be chosen to satisfy both specifications (or perhaps it can't now, and may be why I can't find a current MTF-94 compatibility claim for their 10W40 EE nanodrive).

Thank you for that reply. I concede that the scales are not set the same way, although I would still doubt the Millers claim for the 10W40 engine oil to fully satisfy the spec for MTF94 - on looking up the technical specs for both, there are some significant differences in the viscosity figures, and I find it difficult to believe the engine oil spec would satisfy the extra long service life specification which was the principal feature of MTF94 (changes at 100k+ miles rather than 30k to 40k when Rover specced 10W40 for the PG1).

The disappearance of MTF94 from the compatibility list for the Millers EE Nanodrive might be as a result of that oil now being fully synthetic only and no longer the mineral/fully synthetic blend which previously classified it as semi-synthetic; Millers Trident Professional semi-synthetic 10W40 does still carry MTF94 in the compatibility list (specifically for Renault applications), although my doubts remain.

Regardless, the age and type of ownership that most of the Rover PG1s are now at, I would think they will almost certainly be getting gearbox oil changes at relatively low mileages and certainly nowhere near the 100k+ specified for the MTF94, and it is therefore unlikely that using a non-longlife oil will be of any great detriment.

[Johnny 216GSi]

You're right . Miler's Trident oils now claim MTF-94. Land Rover spec., too.

Last line of the compatibility list:



Here's a chart showing SAE gear and crank oil scales and what they mean with respect to real kinematic viscosity. A 40-grade crank oil (labelled "auto" on the graph, just "car" in US-speak) is clearly in the correct range for 85 winter grade / 90 grade on the gear oil scale. These figures are slightly high with respect to the MTF94 spec, which is typically equivalent to a 75W80 gear oil. However, since Rover states PG1 boxes primarily require a 10W40 refill, this oil's svhievement of a slightly thicker gear oil spec. is neither here nor there. I'd be very happy to put this oil in a PG1 box, myself. And if and when I do a box refill, I'll probably buy this now I know this is the current Miller's oil that is stated to meet all possibly relevant specs. for the PG1.

[Stan Thomas]

I use Millers EE 10w/40 fully synthetic in my GSi 420 ("T" series engine), along with their recommended fully synthetic gearbox oil.

I had first spoken to their technical department, and they advised not to use this oil if the engine had been overhauled, but to run it in with a mineral oil first - otherwise the superior benefits of a synthetic oil would considerably delay the process. However, as the engine had already done 35K miles I went ahead, and after 10.000 miles it does not even need topping up,and there appears to have been a slight increase in M.P.G.

So yer pays yer money, and makes yer choice!

P.S.
I also recall having a "clunky" gearchange on a new Triumph motorcycle for which I had treated to fully synthetic oil - but the factory said it would not improve until it had run-in on a mineral oil for about 5 to 8.000 miles - again endorsing just how superior quality a synthetic product can be.

Regards to all,

Stan.