Years of fooling about and trying pretty much EVERYTHING thats on the market
Endless discussions as far as what oil I should use, in which case.
You will hear thousands of different opinions regarding which oil is best, statistics which mean nothing really, tests that all companies make showing that their oil is THE BEST and so on....
In the years of my experience and personal testing though, THIS will be my bible from now on, and I'll be sticking to it.
Today I will let you know of my findings regarding GEAR OIL
and I will share with you my personal views on the subject.
You can take my advice if you like
Most people think that the A and Z with oils, is to be as thin as possible and not breaking up under high temps, in order to have the less friction, but at the same time stick to the metal parts in order to keep them lubricated.
In short, this would be ideal, and this is what I thought as well, but never been able to know if what I was using would provide me with such results.
In theory, oil is oil, even if you use engine oil in your gearbox, it will still lubricate it, it wont go black, it wont overheat in normal driving conditions etc, but this is just HALF of the story.
But do you just want to lubricate your gearbox, so it wont seize ? or do you want to protect it ?
Oil can not only break its velocity under heat, it can also break under pressure !
So, a gearbox needs a HIGH PRESSURE OIL in order to cope under the extreme conditions of a gearbox (torque converter).
These oils are either branded with EP
(extreme pressure) or GL
(as in GL3, 4 and 5)
Grades 4 and 5 of pressure, (more pressure) are used in gearboxes with LSD, which obviously stresses out the gearbox more and produces more pressure.
oil companies, in order to achieve these extreme pressure withstanding conditions, add microscopic parcels of metal in their formula.
You will hear LOTS of people saying that you shouldn't use GL5 oil in your classic car's transmission.
This is true, but why ?
Because the formula which contains the microscopic parcels of metal (GL4, GL5), will also have a CHEMICAL reaction with your old gearboxes bronze parts (synchro's) and destroy them.
There are GL5 formulated oils that are NON METALLIC
Which is what I used and tested in my Sprint for many years, and had NEVER EVER had any problems with crunching 2nd gear or noisy diff or breaking a diff- which are all common problems with the boxer family gearboxes.
Regardless of the MAKE of the OIL that you use in your gearbox from 1970's till today, make sure that you use a NON METALLIC FORMULA OF THE GL5
or if you cant find a GL5 which is non metallic, go to less pressures like GL4 or GL3 , again non metallic.
I was told that the GL5 might stiffen up my gear changes a lot, but I used it anyway, and it had no effect on my gears.
The grade of the oil I'm using is 80W90, which is the ideal grade.
For EXTREMELY freezing temps , you can use 75W90, but you wont need it, even in UK.
Although its a bit hard to explain grades, I'll give it a shot :
The higher the gap between the grades (5w50, 10w60, 75w140 etc) the more you can "strech" the oil before it brakes up.
Think of a bubble gum, if you take it and stretch it, the 10w60 buble gum will stretch to , lets say, 10 cm , while the 80w90 bubble gum will stretch up to 3 cm before they snap.
Again, IN THEORY, motor oil companies have formulated these high velocity grades to keep the breaking "lines" as big as possible.
However ! When those lines DO BREAK, which oil will give you the biggest gap of unlubricated parts ?
You guessed it, its the 10w60.
So , the shorter the gap between the weight and grade, the less possibilities you have of damaging something when the oil breaks.
If even now, you believe that you want to put normal 20w50 engine oil in your old transmission, please note that you should get a NON FOAM
formula of the 20w50 oil, as normal oil usually foams up after stirred up by the diff and gears, and that will cause you a big problem (apart from the noise of the diff which you will also inherit).
So, again , gear oil : 80w90 - Non Metallic Formula GL5
Engine oil is a different story, so will get on that later