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MG Midget and Sprite Technical - Diff oil advice

I'm looking for a little guidance please?
I've searched through the archives but it's still not clear to me what is now considered a suitable oil for the differential.

In a discussion, Nigel A used mobilube 1 shc 75w-90 and said it was worth a go however, its spec notes it's GL4 and GL5.

Now I've also read that we shouldn't use GL5 in a period hypoid diff as you need to protect the yellow metal components, and GL5 won't do that.

To confuse matters further, it seems the originally recommended EP 90 coding has now changed to 70w 90 or SAE 90 - 140 e.g. Penrite Mild EP: "to be used in place of SAE 90 & 140 oils."

My question is BBS; what specification - not necessarily brand, should I be looking to use?

Many thanks.
Philip Sellen

Philip,
if you want EP90 you can still get it and it'll be GL4 so as not to frighten the horses. Just one example, Castrol Classic Oils (an MGOC subsidiary) - https://www.classicoils.co.uk/ep90

I know you want the views of others but I wasn't the only one to use Mobil 1 SHC GL5, have a look in the Archive. What you've read is out of date by many years (decades). It was also considered OK to use GL5 in the diff as it didn't get as hot as a gearbox, and anyway modern blended GL5 won't "attack the yellow metals", I use a modern GL5 in my diff! - and Ford T9 gearbox!!

Going back as many years as I can remember MGOC Spares have sold Castrol EPX 80W/90 GL5 for the 1500. - https://msdspds.castrol.com/bpglis/FusionPDS.nsf/Files/1425EFE45BBA5B5880257837006A76DB/$File/BPXE-8E5P88_0.pdf
Nigel Atkins

As you say, EP 90 doesn't really exist anymore. It is all multigrade xW-y grade oils.

I would look for a xW-90 type oil (assuming that the hot rating is more important than cold). Most commonly that would be an 80w-90 or a 75w-90.

EP rated and/or designed for hypoid gears.

GL4 and/or rated as yellow metal safe, so as not to attack the thrust washers.

Cheers,
Malc.
Malcolm

Malc,
have a look at my post just before yours.

I'm also not sure why, other than advertising, those proudly owning British cars don't go for oils from British blenders rather than those from overseas, if they're of the same quality or better that is. I'm not against goods from overseas but if we've got good local stuff available makes more sense to use that.
Nigel Atkins

My preffered local blender has gone on holiday! ha ha!

http://www.westwayoils.co.uk

Malc.
Malcolm

You can get ep90 gl4, and it is 'cheap' if you buy in bulk.

https://www.ebay.co.uk/itm/373537080798
£21.99 5litres, including post. £4.40/litre.

I bought some and have it in my diff. Smells the same looks the same, and they have good reviews.

"Who are Smith & Allan?
One of the UK's largest independent lubricant manufacturers

The production of Smith and Allan lubricants dates back to 1925, the intervening years have seen us forge strong and lasting relationships with the world's largest additive manufacturers and in particular with Shell Oils."


anamnesis

Okay thanks,

So while GL4 is still available from some outlets, it’s now considered that GL5 is fine for use in the diff.

In addition, a 70w (or 80) 90 would also be acceptable in either GL4 or 5 specification.

In which case, I’ll see what I can find online.
Philip Sellen

Millers
. Classic Gear Oil EP 80w90 GL4 - https://www.millersoils.co.uk/products/classic-gear-oil-ep-80w90-gl4/

. TRX Synth 75w90 (GL5) - https://www.millersoils.co.uk/wp-content/uploads/2019/11/TRX-Synth-75w90.pdf

and the one I use - CRX 75w90 NT+ - https://www.millersoils.co.uk/products/crx-75w90-nt-2/
Nigel Atkins

ETA: Shop around, I got Millers for my wife's car at half price a couple of months ago, and from a place that's normally expensive.
Nigel Atkins

I took David's advice ( I think it was him) and bought that EP90 from Smith & Allan for my Frog. Seems ok and a sensible price.
GuyW

I too thought it was David Smith that put he bought EP90 from Smith & Allan so with my memory I had to check the Archives, and he did.

- But -

Second result gave me a post from David in May 2011 (over 10 years ago). -

David Smith, Berkshire, United Kingdom - Posted 11 May 2011 at 18:45:03 UK time

"GL5 EP80/90 in the diff will be fine for less than average usage; there is anecdotal mention that the GL5 additive pack 'may' degrade the yellow metal washers; if the diff needs rebuilding afetr 50k miles instead of 100k miles, is that a big problem to you?
I found at least one research note on the net which stated that GL5 standard has been updated and the additives modified to *not* attack the yellow metal in the way it used to.
My advice - do your own research and reading (google etc) and come to your own conclusion, based on your own usage profile and appetite for risk.
FWIW I use GL5 75W/90EP in the racer's diffs and only ever broke one - after all the oil leaked out!"

Plus on that 2011 thread I found the British Motor Heritage labelled (Duckham's Q) EP gear oil that is GL5 and approved -
"... for SAE80 or 90EP or Hypoid Gear Oil. Compatible with the non-ferrous transmission components of early transmissions. Meets API GL5/MIL-2105B Technical Helpline 0181 2908207"

I distinctly remember buying a bottle of 80/90 diff oil from Brown & Gammons and was given a bottle of that Heritage labelled oil which to my surprise at the time was GL5.

Use whatever oil fits your belief, suits your wants and needs, keeps you happy and gives restful sleep.
Nigel Atkins

Thanks again for the links and comments.

It’s established now that there are a range of oils that can be used in our period diffs, including some GL5 specifications that state they are not detrimental to yellow metal components.

Whilst it’s good to have a variety of options to choose from, it can also be difficult to decide what suits your use best. I don’t do track days, hill climbs or considerable mileage each year, so the GL5 you quoted from Nigel, would probably be okay.

However, I’m still drawn to a GL4 specification so it’ll probably be the Millers you linked to earlier.
Philip Sellen

Philip,
IMO as a total non-expert in anything including oils the other oils are fine but I just favour a local blender and I think you going for GL4 will ease your mind and a 80w90 will be a little better for driving in those fabulous dry sunny but colder winter days when there's not been salt on the roads to worry any one.

If you can get the back axle as warm as possible (easier way is to go for a good spirited drive) to drain out as much of the existing oil and leave to drain as long as possible. This way there will be the least old oil left in to dilute the new fresh oil going in.

For obvious reasons do remember to check the filler/level plug comes fully out BEFORE removing the drain plug. And take the opportunity to remove and clean the plastic axle breather pipe and cap.

IF you find the diff quietens, I'm afraid that won't last long.

ETA: do shop around for price.
Nigel Atkins

Hi Guys,

Just make sure you use an oil which is designed for HYPOID differentials!

I know very little about oils, but I do know that many years ago, my late brother got advice from a well known oil manufacturer. My brother wanted the best oil for his TC race car which has a 4.2 Spridget diff grafted in. The recommendation was to use an "old fashioned" oil which he then tried. Each lap at the next race meeting, his car whined more loudly. The diff was EXTREMELY hot when he pulled into the pits. The pinion teeth were worn to the point that the tops were sharp! His oil was not suitable for HYPOID applications.

Cheers from South Australia,
Bob Schapel


R L Schapel

This thread was discussed between 06/08/2021 and 08/08/2021

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