Selection of the Right Motor Oil for Classic Mini Engines

Click here do download the pdf file

Introduction                                                                 
There is a lot written about what is supposed to be the right oil for classic Mini cars, vans, and pickups, where the transmission is under the engine, using the engine oil as a transmission (or gearbox) oil.

Unfortunately, most of it is written from the point of view of simplicity, usually recommending a SAE 20W-50 viscosity oil, without any further explanation or specification. While that viscosity will work in these engines and transmissions, it will cause excessive wear in any engine in good condition. Over the years, Austin, Morris, British Leyland, and Rover published various recommendations, from 10W-30 up through 20W-50 for certain conditions.

And while some people realize that the standard modern car engine oil of today no longer has the level of ZDDP (anti-wear) that the Mini needs for gear and flat-tappet engine protection, they are often misguided by companies that sell very obsolete oils, or in at least one case, an oil with way too much ZDDP. So much that it will, according to the Society of Automotive Engineers, damage the cams and other parts. Few understand that a simple API CI-4 diesel (or even CK-4) formulated engine oil has all the ZDDP we need in these cars.

Also, very few people with Minis that are equipped with the AP automatic transmission understand that modern engine oils, with their gasoline saving friction modifiers that cause slippage of the clutches, will shorten the life and performance of the AP transmission. That this transmission should use MA2 motorcycle oil for best performance and longest life of the clutches. And should also use 10W-40 viscosity, as that desplaces best from the clutches.

So this paper addresses the needs to these engines and the reasons why it is best to use only use an oil so viscous (thick) as 20W-50 when the engine and/or transmission are well worn, and don't build enough pressure in the engine or cause excessive noise in the transmission. That, when rebuilding a Mini engine, if done right, you should go back to the original recommendation, which would generally be a 10W-40 viscosity.


This is the current draft of this paper.  I’m sure there will be additional questions that will arise or points that I haven’t explained to the satisfaction of some readers.  Please send your questions or suggestions this email. and I will answer them in the next draft.


Click here do download the pdf file on oil for Minis                            Current update is August 24, 2019.  This is the fourth edition.

For those who want more detail on the use of ZDDP or its minimums and maximums, I suggest reading my detailed paper on oils for flat-tappet engines.

Click here do download the pdf file on flat tappet engine oil.

Hope you enjoy your Mini as I enjoy mine, and have lots of trouble-free miles.