Mixing GL-4 with GL-5

Apr 5, 2018
I know there are tons of threads about this in BITOG, however i couldn't find an exact answer to my question and decided to start a new thread. Sorry for that :)
I had hard gear shifting issue in the past. I solved it ( by help of you in this forum) by using thinner oil. I Used Ravenol 75w-85w (GL4/GL5) https://www.ravenol.de/en/product/g...e-und-antriebsachsen/ravenol-mtf-1-sae-75w-85

I passed the car to my father who is living in the village. He took it to mechanic, for engine oil changing. At that time he added 300ml of Lukoil GL5 oil.
Oil capacity is 1.6L
I am not sure if it is high enough to cause issue in long term ? Or is it too low to lose sleep over ?

As Far as i know, oils that has both GL4/GL5 ratings use modified type of phosphorus Sulphur in order to protect synchronizers.
Not sure if GL5 alone has the same type of additive or conventional phosphorous Sulphur that will eat the synchro's.
I made some research on google, Some people says almost all modern GL5 are safe for yellow metal regardless of having GL4 rating on them, because additives used both GL5 and GL4/GL5 are same.
Somewhere around 30 years ago a deactivated or buffered sulfur was developed that would react with the phosphorous to create the protective/sacrificial layer in the conditions created in the gear boxes (temperature and pressure) without being corrosive to the brass, copper, etc. This additive system is used in most gear oils today.

Another quote
A traditional GL-4 gear oil of any given viscosity has about ½ of the level of sulfur/phosphorous additive that would be in the GL-5 product, so the bond is not as strong, and therefore can be peeled off without peeling a layer of brass (or less brass). This means that the GL-4 product provides a little less extreme pressure protection, so in the differential of a high-powered car, it would not be the ideal product in the differential. To understand this need we should be aware of the fact that the differential is where the final torque is applied to the wheels (in most applications).

So does this mean, even if the GL5 in my gearbox is active phosphorous Sulphur, it is totally safe, even in long term, due to lower level ?

Just have too much headache with that gearbox, which is running fine for now, i do not want to deal with new issue :)
So i may sound paranoid :)
As long as it still shifts well, I would not lose sleep over that small amount of added GL5. I have done exactly the same thing you described with topping off the manual gearbox in a family member's Nissan with conventional 80w90 GL5. It's still shifting well at 400,000 kilometers.
Okay, I'm not sure on the technical about the Gl4 vs Gl5. I'm sure someone else can fill the gap. I'm not also sure on you're ability to work on cars.

But I would just change out the 2 liters of fluid with new GL4 fluid.
For 40 dollars in fluid, I would do it for the peace of mind.
But how many miles since last change? Maybe it's due anyways.
Hi Thanks for replies.
İt is 40K KM since last oil change. I think it can go as high as 100.000 Km Right ?