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MG MGB Technical - OD Trans. Oil Change

I was getting ready to change the oil in my OD transmission with 30 weight non-detergent as usual. Unfortunately I did not have any on the shelf only the 20/50 I use in the engine. Before I changed the oil with the 20/50 I decided to check the archive. Answers are all over the place 30 detergent and non, same with 40, some use 20/50 and one even recommended using 90. I decided to wait and get what I have been using.

What is the present "definitive" oil that should be used?
Lee

Factory recommended engine oil - 10W40 or 20W50.
Chris at Octarine Services

An interesting article:

http://www.quantumechanics.com/categories.php?op=newindex&catid=11

warmly,
dave
Dave Braun

don't use 90W, it makes the box run a lot hotter.
dominic clancy

Dave,

Great article. I will definitely stay with the 30 weight non-detergent.
Lee Sheldon

Not such a great article:

The OD they tested was an early A type - not a D or more common LH type found on the MGs.

They didn't use 20W50 or 10W40 oil to test!

LH types in good condition develop 400 - 420 psi on 20W50 or ATF.

Overdrive Repair Services ( the successor to Laycock) say that the LH OD will work on any oil between ATF and 90 weight gear oil - the determining factor is the box not the OD!
Chris at Octarine Services

It would seem logical to do what Chris posted and use the oil recommended by the maker! or is 20/50 hard come by in the States nowadays? You have to go looking for it in this country but it's still relatvely easy to get.
Ron
R. Algie

A 20W50 mineral will become a 20W30 in no time at all, but all the viscosity improvers are now chewed up and left in the box. An engine oil contains detergents and anti wear additives. A box oil contains Extreme pressure additives which are now in a safer form since about 2000. ATF is a 5W20 and gear oils are measured on a different scale to avoid confusion, so a 80W90 is only like a 20W50 engine oil.

At the end of the day most mineral oils will end up about a 30weight and it depends on whether you want cold performance and the right additives.
Paul Wiley

20W/50, 15W/50, 15W/40 doesn't really matter, all were recommended for both hot and temperate climates. Only cold climates (consistently below -10C/15F) used 5W/20 or 5W/30. This is for engine, gearbox and carbs.
Paul Hunt 2

Lee

I have the same issue. I have read John Esposito's article and have actually talked to John about this. He is still recommending 30wt. My rebuilder (not John) is recommending same oil that I run in the engine 20/50.

He had my unit on a test bench and showed me pressures. With 20/50 the D type OD was functioning to nearly perfect factory specifications.

Given John's reputation, I would be comfortable with 30 weight, but given my rebuilders recommendation and now Chris's, I am going with the 20/50.
Bruce Cunha

Hi Folks:

I think the primary issue is not the viscosity, but the detergents in the oil. To my knowledge all mutigrades use detergents. The reason John Esposito recommends the 30W non-detergent is because of the foaming problems in high pressure hydraulic systems. 30W non-detergent oil is often refered to as "compressor oil". and partly used to prevent foaming. My past experience with aerospace products is that you do not want foam in a high pressure hydraulic system, which could cause component/pump high cycle fatigue, etc. I even had a Buick V6 3.8 liter hydraulic lifter(s) crash due to foam. Had to wait until it cool down to restart.

Good Luck: Rich Boris 67B roadster
Rich Boris

After reading through all of the recommendations I decided to do the most logical - refer to the original owner's handbook that came with the car. It reads on page 64 as follows:

Key to Recommended Lubricants:
Engine, Synchromesh Gearbox, Overdrive, Distributor, Carburetter and Oil Can.
All temperatures above -12C, 10F
Castrol GTX or Castrol XL 20/50

For those of you who live in colder climates:
-17 to -7C, 0 to 20F
Castrolite of Castrol Super

Below -18C, 0 F
Castrol CR 5/20

The recommendations include other motor oils, I only listed Castrol since this has been my brand of preference.

Thanks for all of your responses.
Lee

Timely thread. Having just turned 100k on my 79 mgb, I am about to change the transmission and diff oils. Using a Haynes mgb manual, I am looking on page 118 & 119 to find the fill plug for the oil. My car is the manual gearbox WITHOUT overdrive. Obviously I do not want to drain the oil and not where to refill the box
BTW, the Haynes manual suggests using 20W50 Castrol GTX multigrade as listed on Lubricant & Fluids page.

So, does anyone know where the fill plug for the transmission is located??

Thanx

cheers

Gary :>{D
79mgb
gnhansen

Gary: The fill plug on later MGBs is located on the right side about half way up. You will need a small hand pump, available at auto stores, to fill the trans without making a mess. Ray
RAY

I use Redline MT90 Synthetic oil in my overdrive transmission. I've studied the properties, talked to Redline and feel it's the best choice for me.
CD Dewey

This thread was discussed between 17/11/2006 and 28/11/2006

MG MGB Technical index

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