Rear diff fluid type ?

It’s synthetic and had the additive , they didn’t have any Lucas that didn’t have it

 

Kinda weird though I added all three quarts and it barley dripped out at all

 

Were you sitting level when you changed it? It’s not like the diff is going to blow up if the fluid level isn’t perfect.

 

I read to drain it, fill it till it runs out, wait like 10 minutes, then fill it till it leaks again. What procedure did you follow?

 

Yes it was level, I fillled two quarts then waited five minutes then put the last quart, I’m guessing it will be fine

 

I am not expert... but perhaps add some more just to be safe? Any experts with ideas?

 

I’m not sure how much is supposed to drain out but it did start to drain a little bit probably a few oz. from what I’ve read it seems everyone says 3 quarts so it should be okay

 

Ok cool I bought 3 quarts tonight for Saturday so... I'm hoping it goes well

 

yea it’s super easy, just like changing the oil, but two bolts. Hardest part was cranking the bolt off, damn thing wouldn’t budge had to bust out the breaker bar

 

It doesn't get thicker as it gets hotter. If someone invented an oil that got thicker as it got hotter they would be a billionaire.

75w90 oil, when cold, has the viscosity of cold 75w, and when it's hot it has the viscosity of hot 90 weight.

 

I’m inclined to disagree with you. There’s an additive that’s put into oils thats called a viscosity improver (vi). A winter weight oil when it’s cold (75w) is thinner so the gears actually move and bearings actually get lubricated. Imagine 140 in the morning after a 30 degree night. Thus muti weight oil. Read about it, takes some classes in oil analysis and get some certification it the subject matter and then we can talk about this.

 

For someone that seems to "know" a great deal about oil and throws out all these humblebrags, you are the one that seems confused.
Motor oil grades are NOT same as gear and axle oil grades, its all about the additives. Both are graded differently.

At the end of the day we are talking about a frigin differential. It isnt rocket science.

$29 75w-90 Synthetic Gear Lube - 1 Quart (Pack of 2)

75w-90 all the way to 85w-140.. will work.

 

Of course 140 will work!!! As I stated originally, it will just reduce efficiency. They are all graded differently but it all means the same. Viscosity index (vi), ssu or iso all are measures of viscosity relative to temperature.

 

it takes a long time for the oil to creep out or into the axle tubes

Go on high way for a good run before draining it

 

@maxtherat

Allow me to educate you.... from Wikipedia:

"This is because as all oils thin when heated, so to get the right film thickness at operating temperatures oil manufacturers needed to start with a thick oil to achieve this. This meant in cold weather it would be difficult to start the engines as the oil was too thick to crank. However, as oil additive technology was introduced that allowed oils to go less thin as fast (i.e. a higher viscosity index), this allowed selection of a thinner oil to start with e.g. a product that acts like an SAE 15 at cold temperatures e.g. 15W (W for winter) and the end part its performance at 100C,

The SAE designation for multi-grade oils includes two viscosity grades; for example, 10W-30 designates a common multi-grade oil. The first number '10W' is the equivalent grade of the single grade oil that has the oil's viscosity at cold temperature and the second number is the grade of the equivalent single-grade oil that describes its viscosity at 100 °C (212 °F)."

You're welcome

 

Hey Max, I read about it, I took some classes and I got certified. I'm now as smart as you. So tell me about how oil gets thicker as it get hotter?

 

...is the "special additive" the end result of the $238 hand job?

An electric torque wrench helps too.

 

@maxtherat

The viscosity of oil is inversely proportional to temperature. That is, as the temperature of the oil increases, the oil's resistance to flow decreases. Additives are added for a number of reasons; to use your example, "viscosity improvers" are added to oil to increase the oil's resistance to decrease of viscosity. Those viscosity improvers are typically polymers which, regardless of chain branch structure and composition, have a particular drawback: they're susceptible to degradation under sheer stress - the type found in differentials. At a certain point, those molecular chains will break apart and fail, and when they do, the protection provided by those viscosity improvers will be negated.

Normally I would have left this alone, but you have claimed superior knowledge gained from courses of "oil analysis" and related certifications. Yet you seem to be confused about basic physics and rheology of oil which, I would assume, would be fundamental in any curriculum dealing with comprehensive "oil analysis".

 

To @jross20

Buy three quarts of your choice of synthetic gear lubricant. My personal preference is Mobil 1. Once I allowed the differential to drain for about twenty minutes (great time to have a beer if you're so inclined), I added 2.5 quarts and let it sit for about ten to fifteen minutes. I then gently drove it around for a few quick miles, and afterwards I added the final half quart and the level was perfect. Buy a fourth quart if you want to be safe; if you don't use it, it can always be returned for a refund.

Just make sure you don't spill the old oil. It reeks.

 

I don’t disagree with you and never made claims of “superior” knowledge as you stated. Do I know a thing or two? Yes. Is my knowledge backed by industry certification? Yes. Am I chemical engineer? No. Do I quote someone else’s words coppied from the internet? No. Shear as you state it is reduced or slowed by EP additives that does not exist in all gear oils. Shear is inevitable but the initial decline in an oils viscosity is “typically” greater as the viscosity index increased.