85w90 -vs- 80w90 ????

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What is the difference between 80w90 gear oil and 85w90 gear oil?

I know that the 85w90 was the standard gear lube for umpteen years. I am asking because 85w90 oil is $3 a quart and 80w90 is between $7 and $10 a quart. Synthetic 75w90 is between $12 and $15+ a quart.

Is the 80w90 a semi synthetic?

Is there anything wrong with running 85w90 if the manual calls for 80w90? I am guessing that I might get a slight drop in fuel economy when the lube is cold, but that is all. The ability to lubricate the gears should still be the same.
 
Gear oil is rarely changed, once every 4-5 years and the amount is 1 or 2 quarts. I think you're better go with 75W90, Autozone and Pep Boys has M1 75W90 for about $9-10/qt.
 
What vehicle is this for? 75w90 is pretty common, 80w90 is still spec'd on some cars...but 85w90? Never heard of it.
 
You should look around a little bit more. You should be able to find an 80w-90 gear oil for $5 a quart or less with no problems. Honestly, you should even be able to find at least a 75w-90 semi synthetic cheaper than $7 a quart as well. I buy most (if not all) of my oils either from Wal-Mart or O'Reilly's and they are priced very competitively.
 
If your vehicle gets 15 mpg and you change gear oil every 60K miles, with gas soon to be $4/gal you only have to get 0.1% better mpg with 75W90 to pay for it. The better lubrication at low temps will be for free.
Actually mpg difference is likely to be 1-2% or even more, especially if you don't drive long distances.

Charlie
 
I have Amsoil 75W-90 SVG in both my front and rear diffs. I was just looking at different gear lubes, and wondered why the price difference. My manual says front diff is 80w90 ans rear is 75w90. I just have an obsessive compulsive need to change my fluids, and would rather spend less $$$ if I can.
 
What's better to use then, 75w90 or 85w140 if you had to pick one and money was no object (the 85w140 is like 3 times as expensive)..?

What advantages and disadvantages do either have?
 
Amsoil also has a Severe Gear Oil weight of 75w110 that flows like a 90 weight and protects like a 140 weight gear oil. Many Many choices. I run Mobil 1 75W90 in the open differential of my Mercedes. I previously ran Lucas 80W90 gear oil in the diff for 1700 miles but decides to change because I had some severe clunking issues and also it kept my tranny from upshift and downshifting sometimes. Maybe its because of its gear climbing additive. But I dont like it, so I drained it. It is running much smoother and quieter now with Mobil 1.
 
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