SpitfireS: I don't drive my car during the winter season so when I finally get to take it out again around April when fresh fluids it's almost like a new car again in the beginning.
So no I haven't noticed any subtle changes like that.
I always do smell tests but I don't think I noticed much difference between the Castrol oils, they both smelled pretty bad which seemed good
They are both GL5 only though unlike the Motuls.

Rolan: There were just lots of black metal paste, no larger bits.

 

My diff fluid is due for a change. So I just bought some Mobil1 75W140 since it is readily available (it's actually on sale at PepBoys online too). I noticed on the bottle it says LS (limited slip), and I don't think it comes in any other way. I read most of this thread a few days ago, and it was probably mentioned that our diff doesn't need LS additive, but having it in the gear oil won't hurt the diff in any way. Is that correct?

 

If it states GL5 it's OK. LS additives won't hurt but are not necessary. GL5, though, is.

Much debate regarding what grade oil in this thread but I'm convinced 75W-140 will be fine and will be using it later this fall.

-- Chuck

 

Yes, I made sure it is GL5. Did some search afterwards and don't think they come anyway other than LS any longer. Either 75w140 or 75w90. I agree that the 75-140 is fine based on everything I've read.

 

i have discovered that the SAE J 2360 norm is more demanding than the GL5 norm:
https://www.sae.org/standards/content/j2360_201204/

It exceeeds GL5. It´s worth looking for this norm on the oil bottle, i think.

 

Copy that. I wonder how the paste formed...

 

75w-140 will be fine but totally unnecessary unless you are planning to race Le Mans 24hr or do a track day in Death Valley.

Cheers,

Guy

 

hey guy, so is there any downside to using it? Usually there are always trade offs, othwise I dont see why you regard it for a "le mans"? If the prices are equal to the thinner versions...

basically you imply you regard it better than thinner, otherwise why would you mention heavy usage?

so whats the downside? Just wondering the logic

 

One downside would be higher fuel consumption due to the thicker fluid demanding more engine power to turn the diff. Might be a negligible difference when compared to a lighter oil but a difference nonetheless. He mentioned "le mans" because he's trying to illustrate that unless you're running gruelling endurance racing like that where the fluid is under much more strain and lighter fluids can oxidise or thin out too much due to the heat, the 75W140 oil will hold up longer.

 

okay thats a theoretic downside. But I highly doubt this small difference in viscosity will cause a relevant mpg change. Lets say you average 25 mpg. Do you think it will drop down to 24 or 23? Just from this tiny difference?

its like saying the engine uses more gasoline if you run 5w40 vs 5w30. I can confirm thats not the case...

Besides, it is said that a thicker oil in the diff reduces friction between the gears, which I think would mean a better mpg. So its not so simple I think to make conclusions on mpg.

So if the 75w140 will hold up longer, why wouldnt it be the reccomendation for everyone? It doesnt sound very logical... There must be another reason