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Old 03-05-2009, 09:21 AM
Thread Starter
Join Date: Dec 2008
Posts: 94
Question Gear Oil 75w or 80w ?

Changing my axle fluids, just wondering wether I should you 75w-90 or 80w-90 .... what is the real difference between the 2? which one would be better

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Old 03-05-2009, 04:16 PM   #2
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Join Date: Feb 2007
Location: LITH IL
Posts: 1,633
75W-90 is what you should use. 75=weight. Here is some info I found on a quick search.

Why are there different weights of motor oil?
(And which one is right for my car?)

Monograde oils (SAE 30, 40, etc.)
Multigrade oils (5w20, 5w30, 10w40, etc.)

Have you ever wondered what all the letters and numbers on an oil bottle mean? They stand for different oil weights. For example, a bottle that reads "SAE30W", assures that the oil conforms to the SAE's (Society of Automotive Engineers) oil weight or viscosity standards. The "30W" represents the oil weight, and the lower the number, the thinner the oil. Use low numbers in cold weather, higher numbers in warm climates.

Oils meeting the SAE's low temperature requirements have a "W" after the viscosity rating (example: 10W), and oils that meet the high ratings have no letter (example SAE 30).

You can buy oils in single grades for warm or cold weather driving. However, most people prefer multigrades which suit your car during all seasons.

Multi-viscosity grades (for example, SAE 10W-30) will provide a wider range of use and permit you to drive from one climate extreme to another. They are also insurance against sudden temperature change in your own area.

At cold temperatures, the polymers are coiled up and allow the oil to flow as their low numbers indicate. As the oil warms up, the polymers begin to unwind into long chains that prevent the oil from thinning as much as it normally would. The result is that at 100 degrees C, the oil has thinned only as much as the higher viscosity number indicates. Another way of looking at multi-vis oils is to think of a 20W-50 as a 20 weight oil that will not thin more than a 50 weight would when hot.

It is important to use the correct motor oil weight to reduce wear on your engine. The optimum oil weight for your car depends on the climate you live in, your vehicle manufacturer's recommendations, your driving conditions and the maximum fuel economy you want out of your car
(the lower the weight of the oil, the greater the fuel efficiency).

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Old 03-05-2009, 08:15 PM
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Join Date: Dec 2008
Posts: 94
Thanks thats some good info, I had an idea of what the numbers ment. I figured the 75w-90 has a higher range and 75 is less dense but I just wanna make sure that I will be fine with 80w because my mechanic already bought the 80w I just wanted make sure it wouldn't do any harm, but im sure it wont hurt but I AGREE the 75w would be better
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