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Synthetic Oil In Classic Minis?


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#16 ImagoX

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Posted 16 July 2007 - 09:15 PM

You might be even more surprised to know that the European technical centre for the World's leading lubricant additive supplier is about the same distance from you and that's where I work !!! :shifty:


Thanks for chiming in, Grayedout!

So can you confirm what we're talking about here then? Sounds like you have valuable insights. There's a lot of anecdotal info out there on this subject, backed by few "hard" facts (some contradictory) - so far the letter from Mobil advising to not use synthetic due to the differential sharing the same oil supply seems to be the best piece of hard evidence in favor of Castrol GTX or another good petroleum-based oil. What are your feelings about all this? ;D

Edited by ImagoX, 16 July 2007 - 09:17 PM.


#17 Grayedout

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Posted 16 July 2007 - 09:45 PM

As you might imagine selecting the correct lubricant and additives for a particular engine is a huge problem and especially one like the A-series that shares engine and gearbox.

One of the first problems is 'synthetic' oils can actually be mineral as many years ago the American High Courts decided that heavily refined mineral oils can be classed as synthetic !!!!! The best way to consider it is you simply get what you pay for with oils and if a 'synthetic' is cheap then its almost certainly not !

In terms of seals then Yes oils can contain an additive called 'Seal Conditioners' which "Swell the elastomeric engine seals to prevent fluid leakage." Obviously if you switch between oils with and without these then it can cause variations in the seals and probably leaks!

In terms of the best oil for the A-series then again its a big problem.....the engine would run fine on a quality synthetic such as a 10W30 or 5W30 BUT the gearbox probably wont !!! I am not a gearbox expert so I am not sure why this is so but I have spoken to many experienced engine builders who say anything less than a 50 grade causes premature gearbox wear !

Therefore you are actually selecting the oil to protect the gearbox and not the engine !!!!

I've heard very good things about Valvoline Racing 20/50 whic I'm sure you could get in the States so this may be a good option !

Personally I run Duckhams 20W/50 and change it not much over 5,000 miles !

Hope this helps !! :shifty:

#18 mini93

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Posted 16 July 2007 - 11:12 PM

sorry, not read all the thread but iv heared that synthetic oils milicules are different, and so with the gearbox in the engine sump the gears chew the synthetic strands, and this happens doesnt protect your engine as well
dont know why iv just heared it, i imagin its to do with flowing or how it sits behind bearing face/races and on engine bore, if its too thin wont it bypass the piston rings causing oil burning?

#19 Grayedout

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Posted 16 July 2007 - 11:25 PM

sorry, not read all the thread but iv heared that synthetic oils milicules are different, and so with the gearbox in the engine sump the gears chew the synthetic strands, and this happens doesnt protect your engine as well


Not true and can in fact be the opposite !!

The molecules you are talking of are called Viscosity Index Improvers (VII) and are the things that make a multigrade oil ! Without them oils would be 5W5 or 20W20 or 50W50 !

They are what are called long chain polymers which when cold are tightly packed together like coiled springs and do not affect the flow of the oil.....as the temperature increases they open out into long chains which then get tangled up with each and hence restrict the flow and hold the viscosity higher !

Unfortunately its these chains that get chopped up into smaller lengths and so do not do their job as effectively and so the oil will thin (shear) over time ! They can also have largely different resistance to shear based on their quality (read price!)

A FULLY synthetic oil does not generally need as many VIIs and so does not suffer the same amount of shearing !

#20 mini93

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Posted 16 July 2007 - 11:35 PM

my mistake sorry :shifty: im sure if heared that on here before hmm oh well

#21 Se7enS1ns

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Posted 17 July 2007 - 11:44 AM

So to summarise then - for those of us that have the attention span of a fish - what has been decided as the "best" oil to use in a mini?

#22 ImagoX

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Posted 17 July 2007 - 02:16 PM

Now see... this is an interesting thread - and useful! Does that make me a hopeless geek?

#23 taffy1967

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Posted 17 July 2007 - 02:56 PM

So to summarise then - for those of us that have the attention span of a fish - what has been decided as the "best" oil to use in a mini?


Classic 20W/50 oil like Duckhams Q or that stuff that Halfords sells which has a picture of a Mini on the tin and is actually Comma oil.

If you're rich and have money to burn then you could stock up on Penrite or Millers Classic oil but the best thing you can do is treat you're Mini to regular oil changes with a good Classic oil and then it will take you to the heart of the sun and back before needing attention.

Allegedly! :shifty:

#24 taffy1967

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Posted 17 July 2007 - 02:57 PM

Now see... this is an interesting thread - and useful! Does that make me a hopeless geek?


No, because you're just looking out for you're Mini that's all.

#25 danwebster

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Posted 17 July 2007 - 03:00 PM

The old 'oil' debate......

For the record I run mine on 5-40 fullly synthetic superbike oil.

Make of that what you will.

#26 taffy1967

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Posted 17 July 2007 - 03:04 PM

The old 'oil' debate......

For the record I run mine on 5-40 fullly synthetic superbike oil.

Make of that what you will.


I'm locking myself in the cellar and hiding away at the very thought. :shifty:

#27 Danny341

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Posted 17 July 2007 - 03:05 PM

Well, having just bought a mini, I was gonna treat it to a service over the weekend, And i have a nice tub of synthetic oil lined up ready to go....

Glad i saw this thread now, I may go looks for some classic oil :shifty:

Nice one for the discussion guys

#28 Dan

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Posted 17 July 2007 - 06:37 PM

Whatever Mobil may say, there is little practical difference between the way the diff and the rest of the gearbox handle oil. It is definitely the gearbox/diff that doesn't like synthetic oil though and I have a feeling it's to do with the use of roller bearings over plain bearings. Also I belive that because it is stickier due to the form of the molecules as decribed by Grayedout it doesn't wash swarf out of the synchros as well as mineral, limiting their life. I should say though that this is just the result of lots of reading up about the gearbox and oils in Minis and I'm by no means an oil expert. I think you tend to find rollers in the oil more often when changing synthetic oil. It also seems to hurt the laygear bearings particularly badly.

Guessworks probably pulls apart more gearboxes than anyone else here so he'll be the one who knows about gearbox damage.

#29 ImagoX

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Posted 17 July 2007 - 06:48 PM

The previous owner of my Mini used 10W-30 Valvoline oil (petroleum-based) on all his changes... Switching to a thicker oil might help with my leaking issues. Seeing as how I do not plan to run the car in the depths of winter, I'll switch it to the 20W-50 grade when I drain the oil as part of my gearshift rod seal change... I'll use the High Mileage Castrol formula - hopefully the seal conditioners in there will keep me from developing new main seal leaks.

Thanks to everyone that's contributed to this thread! I feel like I know a lot more about my car now.

#30 redhotmini

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Posted 17 July 2007 - 07:47 PM

20w50 is ideal in any mini engine, as the gearbox runs in the sump.
look at any modern car, and you'll see that they use a thicker oil (like ep80w90) in the gearbox, and a 5w30 in the engine.
now you can't fill a mini engine with ep80w90 gear oil, its just too thick for the oil pump to cope, but will make your gearbox last ages. so the next best thing is 20w50, its thick enough for the gearbox to feel slick without premature wear, and thin enough to pass round the engine's oil galleries and bearings. I run valvoline racing 20w50 (roughly 19.00 for 5 litre) in my mpi, and millers CTV 20w50 in the 1380. the ctv is about 35 for 5 litres, but is specifically designed for gearbox in sump applications like the mini, something to do with the chemical compund, makes it suitable for gearboxes and engines.

the mpi used to run on 10w40, which i think is too thin for any mini, purely because it gives the gearbox very little protection. the gearchange used to be quite notchy and stiff, i put the valvoline 20w50 in, the engine is much smoother running, the gearbox is quieter, the gearchange is super slick now its like a new gearbox. and the annoying leak that nobody could cure has gone!

20w50 is the future!




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