Is there any good reason the service manual calls for 80w gear oil in the front differential while it calls for 75w in the rear? I'm not thinking there's much difference, but this is my first AWD car. Was just going to use Valvoline Synpower 75w for both front and rear. Should I be ok?? In a mineral gear oil, there's a large difference between an 80W90 and a 75W The base oil blend is much lighter, so this means your gear oil will get significantly thinner over time.
An 80W90 will have a higher viscosity base oil blend and much less polymer VII to shear. So, it'll be more consistent in its viscosity over time. Also, the thicker base oil blend will afford better protection to the gears.
I do not know Valvoline's Synpower formulation so I don't know whether it's using a bunch of polymer or not. The difference is that the syn oil starts with a lower initial viscosity 75 which increases as the temperature increases without looking up the spec I can't tell you what the changeover temps are to The 80 conventional oil does the same but starts "thicker" 80 compared to 75 It REALLY doesn't make that much difference because they are not under pressure - it's all "splash".
Aside from the hypoid gear faces, nothing in there is under that much contact pressure and the side bearings don't "care" as long as they have some lube. Beats me HOW you could hurt it, anyway. They tend to go to 10W or 40 in the summer months there even for 5W or 5W engines. Remember - SUB set up their specs with what they had available from whatever manufacturer and are interested in maintaining the LEAST possible spread of components "lean" inventory.
What they spec is what they sell, what they sell is what they spec. I disagree with you about this, aircraft engineer. Gear oils are an area where there's a very significant difference between 'conventional' and 'synthetic' oils, much more so than engine oils.
Gears chew up VIIs quickly, whereas engines generally don't. Also, gears are a place where higher viscosity itself affords a good deal of protection. Thus, the higher viscosity base blend and lack of VIIs to shear make a conventional 80W90 a noticeably better protector than a 75W To answer your question, I use a synthetic 75W90 from a place called Renewable Lubricants.
It uses bio bases, which are outstanding as gear lube bases. Here's where I'm coming from with my statements about gear oils and what they're made of. This is for GL-5 gear lubes for mineral, synthetic, and blend:. Ronald Shubkin. See more nifty technical digest-type stuff here. I haven't seen any "normal" duty car differential hypoids that have the pressure levels that would require anything approaching the EP extreme pressure loads of some power devices.
The SAE number or grade is allocated to assess an oil. For gear oils, the numbers need to be 60 or above. This means that 75W and 80W are both gear oils.
But before we head directly into the differences between 75w90 and 80w90, we first need to know the basic things regarding them. Say like, what really means by 75w90 and 80w90, why should we use them, and where to use them.
SAE allows this designation. The flow characteristics of the oil are especially relevant for multi-grade oil at certain temperatures. Gear oil 75W is used in adverse conditions and is suitable for colder climates and limited-slip differentials.
It is used in many gearboxes for its excellent transmission potential where intense pressure and shock charge are required. The gear oil gives thermal and oxidation flexibility and a high viscosity index. This oil has two numbers and has two grades of viscosity. If we want to operate the gearbox at a low temperature, then the oil must be thinner. Thinner oils help to work more smoothly and freely at a lower temperature.
This gear oil is for service fillets, top-offs, and refills of the API GL-4 gear lubricants and other pneumatic axles. It is an integrated additive device developed from high performance-based oils for high performance, heavy-duty gear lubricants. These lubricants are designed for industrial uses, including heavy-duty axles and final drives, which involve intense pressure and shock loading.
The gear oils might look the same to you as they are both in a liquid state, but the real truth is there are some differences between them. There are some significant differences between them in their configuration, ingredients, usage, type, and many other things that you cannot realize from the outside.
For gear oils, it has historically been those fleet proprietors, and operators have better viscosities. Thick lubricants are, after all, defensive. Gear oil must maintain sensitive axle machinery in excessively challenging environments.
SAE 80W gear oils are based on mineral oil, meaning more frequent oil adjustments. It means it needs more maintenance time. Their thickening at lower temperatures may also affect their production greatly. A wide variety of temperatures is preserved in SAE 75W by a constant thickness or viscosity. In colder or windy environments, it is thicker than 80W when it faces extreme heat and thinner.
While a low cost 80W gear oil may be an appealing alternative, 75W is a better option if we consider the overall cost. It provides both productivity and safety and longer draining cycles, which lowers maintenance costs. Thickness is kind of related to density. This means 75W and 80W are both gear oil. The 75W gear oil is used under extreme pressure conditions and is recommended for limited-slip differentials and for use in colder climates.
Used in heavy duty manual transmissions, final drives and axles, high temperatures will not effect the heavy film left by this oil. The 80W gear oil can be used in extreme pressure conditions and as a lubricant for non-synchronized manual transmissions in heavy duty trucks or buses.
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