Pros/Cons of 75W140 vs 75W90...?
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No need for the thicker synthetic oil unless you are long distance racing. Street driving wont tax a good diff oil. You loose 6-8% HP in the rearend where the power transfer makes a 90 deg turn - why make it worse? Why are you considering the thicker oil? Stick with dino in ther rear member unless you have light duty trucking in the winter. Synthetic anything can make a good formulation challenging, whereas dino based oils are easier to properly additise.
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Originally Posted By: ARCOgraphite
No need for the thicker synthetic oil unless you are long distance racing. Street driving wont tax a good diff oil. You loose 6-8% HP in the rearend where the power transfer makes a 90 deg turn - why make it worse? Why are you considering the thicker oil? Stick with dino in ther rear member unless you have light duty trucking in the winter. Synthetic anything can make a good formulation challenging, whereas dino based oils are easier to properly additise.
I want to know the pros and cons...
Factory service manual actually specifies synthetic gear lube.
You say I will lose 24-32 HP (that sounds over-estimated)...? How do you come up with 6-8%...?
No need for the thicker synthetic oil unless you are long distance racing. Street driving wont tax a good diff oil. You loose 6-8% HP in the rearend where the power transfer makes a 90 deg turn - why make it worse? Why are you considering the thicker oil? Stick with dino in ther rear member unless you have light duty trucking in the winter. Synthetic anything can make a good formulation challenging, whereas dino based oils are easier to properly additise.
I want to know the pros and cons...
Factory service manual actually specifies synthetic gear lube.
You say I will lose 24-32 HP (that sounds over-estimated)...? How do you come up with 6-8%...?
Originally Posted By: d00df00d
It depends. What does your axle specify, and how much power does your car make stock?
GM 10 bolt axle with Torsen.
GM service manual specifies:
Synthetic 75W-90 Gear Lubricant GM P/N 12378261.
Depending on which mods, 350-400 HP at the flywheel.
It depends. What does your axle specify, and how much power does your car make stock?
GM 10 bolt axle with Torsen.
GM service manual specifies:
Synthetic 75W-90 Gear Lubricant GM P/N 12378261.
Depending on which mods, 350-400 HP at the flywheel.
Is there be any problem with the 75W/140 getting to the axle bearings...?
I suppose not because it won't get hot enough to behave as 140...
What are the actual viscosities of 75W/90 and 75W/140 at operating temperature (and define operating temperature)...?
Thanks.
:^)
I suppose not because it won't get hot enough to behave as 140...
What are the actual viscosities of 75W/90 and 75W/140 at operating temperature (and define operating temperature)...?
Thanks.
:^)
How old is that recommendation? The 75w-90 scale was split a few years ago (2003 IIRC) and the thicker half became 75w-110. There aren't many 75w-110 gear oils on the market but I know Amsoil makes one, and their gear oils are darn good stuff.
If you want to go with 75w-90, I would highly recommend Motul Gear 300. That's used straight out of the bottle by full-on race cars. Can't get much better than that.
If you really want to go thicker, you'll want the best stuff you can get so that your temps stay low (thick oil doesn't cool as efficiently). Castrol SAF-XJ would be my recommendation. You can get it from BMW or Nissan dealerships since it is factory and service fill for all the BMW M cars and the Nissan GT-R.
Or, you could just stick with the GM fluid. It's probably fine, to be honest. But that's up to you.
If you want to go with 75w-90, I would highly recommend Motul Gear 300. That's used straight out of the bottle by full-on race cars. Can't get much better than that.
If you really want to go thicker, you'll want the best stuff you can get so that your temps stay low (thick oil doesn't cool as efficiently). Castrol SAF-XJ would be my recommendation. You can get it from BMW or Nissan dealerships since it is factory and service fill for all the BMW M cars and the Nissan GT-R.
Or, you could just stick with the GM fluid. It's probably fine, to be honest. But that's up to you.
Originally Posted By: joecar
Is there be any problem with the 75W/140 getting to the axle bearings...?
I suppose not because it won't get hot enough to behave as 140...
It depends on the oil but the 140 will probably always be thicker even though the winter ratings are the same. Remember that all ratings represent a range.
75w-140 should be able to get in the bearings just fine, and it will lay down a stronger film (all else equal, of course). The difference is that it won't flow through as quickly, which means you'll get hot spots because it won't cool as efficiently, and it'll generate more drag.
Is there be any problem with the 75W/140 getting to the axle bearings...?
I suppose not because it won't get hot enough to behave as 140...
It depends on the oil but the 140 will probably always be thicker even though the winter ratings are the same. Remember that all ratings represent a range.
75w-140 should be able to get in the bearings just fine, and it will lay down a stronger film (all else equal, of course). The difference is that it won't flow through as quickly, which means you'll get hot spots because it won't cool as efficiently, and it'll generate more drag.
Originally Posted By: joecar
Originally Posted By: ARCOgraphite
No need for the thicker synthetic oil unless you are long distance racing. Street driving wont tax a good diff oil. You loose 6-8% HP in the rearend where the power transfer makes a 90 deg turn - why make it worse? Why are you considering the thicker oil? Stick with dino in ther rear member unless you have light duty trucking in the winter. Synthetic anything can make a good formulation challenging, whereas dino based oils are easier to properly additise.
I want to know the pros and cons...
Factory service manual actually specifies synthetic gear lube.
You say I will lose 24-32 HP (that sounds over-estimated)...? How do you come up with 6-8%...?
The difference isn't anywhere near that much at temp...
http://www.redlineoil.com/content/files/tech/Gear Oil Tech Info.pdf
Originally Posted By: ARCOgraphite
No need for the thicker synthetic oil unless you are long distance racing. Street driving wont tax a good diff oil. You loose 6-8% HP in the rearend where the power transfer makes a 90 deg turn - why make it worse? Why are you considering the thicker oil? Stick with dino in ther rear member unless you have light duty trucking in the winter. Synthetic anything can make a good formulation challenging, whereas dino based oils are easier to properly additise.
I want to know the pros and cons...
Factory service manual actually specifies synthetic gear lube.
You say I will lose 24-32 HP (that sounds over-estimated)...? How do you come up with 6-8%...?
The difference isn't anywhere near that much at temp...
http://www.redlineoil.com/content/files/tech/Gear Oil Tech Info.pdf
80w-140 is way way thicker than 75w-90.
Originally Posted By: Ben99GT
Originally Posted By: joecar
Originally Posted By: ARCOgraphite
You loose 6-8% HP in the rearend where the power transfer makes a 90 deg turn - why make it worse?
You say I will lose 24-32 HP (that sounds over-estimated)...? How do you come up with 6-8%...?
The difference isn't anywhere near that much at temp...
http://www.redlineoil.com/content/files/tech/Gear Oil Tech Info.pdf
[Posts trimmed for concision]
ARCOgraphite didn't say the gear oil will cause that much power loss. He said the differential inherently causes that much, so there's no reason to make it worse by going with a thicker oil.
I don't know if the numbers are accurate, but that was the point.
Originally Posted By: joecar
Originally Posted By: ARCOgraphite
You loose 6-8% HP in the rearend where the power transfer makes a 90 deg turn - why make it worse?
You say I will lose 24-32 HP (that sounds over-estimated)...? How do you come up with 6-8%...?
The difference isn't anywhere near that much at temp...
http://www.redlineoil.com/content/files/tech/Gear Oil Tech Info.pdf
[Posts trimmed for concision]
ARCOgraphite didn't say the gear oil will cause that much power loss. He said the differential inherently causes that much, so there's no reason to make it worse by going with a thicker oil.
I don't know if the numbers are accurate, but that was the point.
Hi,
joecar - A good starting point is to use an IR temp redaer to see what the maximum temperature you see. This will enable you to make a better viscosity choice bearing in mind the "shock loading" aspects of course
joecar - A good starting point is to use an IR temp redaer to see what the maximum temperature you see. This will enable you to make a better viscosity choice bearing in mind the "shock loading" aspects of course
Originally Posted By: Doug Hillary
Hi,
joecar - A good starting point is to use an IR temp redaer to see what the maximum temperature you see. This will enable you to make a better viscosity choice bearing in mind the "shock loading" aspects of course
Would you agree, Doug, with the observation that if the oil is kept at its temperature-related viscosity (or close to it) that the "shock loading" part takes care of itself? In other word, keep it cool and in the 90 grade, you would have no shock loading issues.
Hi,
joecar - A good starting point is to use an IR temp redaer to see what the maximum temperature you see. This will enable you to make a better viscosity choice bearing in mind the "shock loading" aspects of course
Would you agree, Doug, with the observation that if the oil is kept at its temperature-related viscosity (or close to it) that the "shock loading" part takes care of itself? In other word, keep it cool and in the 90 grade, you would have no shock loading issues.
Whichever you choose, i suggest not spilling it on your mother in law's garage floor. It will smell. You will be blamed.
Hi,
Jim - Yes as long as the lubricant has the required GL rating this is OK
In shock loading, the worst situations excepted of course (full acceleration (wheelspin) on wet pianted lines then sudden traction on seal) - which can be an issue on heavy equipment!
In my testing I found that most differentials never see more than around 75-90C as a constant operating temperature. My UOAs never showed any evidence of heat degradation even out to and beyond 1m kms OCI
As akways the Manufacturer knows what viscosity is best. IMO it is wise to use the lowest viscosity recommended
Jim - Yes as long as the lubricant has the required GL rating this is OK
In shock loading, the worst situations excepted of course (full acceleration (wheelspin) on wet pianted lines then sudden traction on seal) - which can be an issue on heavy equipment!
In my testing I found that most differentials never see more than around 75-90C as a constant operating temperature. My UOAs never showed any evidence of heat degradation even out to and beyond 1m kms OCI
As akways the Manufacturer knows what viscosity is best. IMO it is wise to use the lowest viscosity recommended
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Originally Posted By: Doug Hillary
Hi,
joecar - A good starting point is to use an IR temp redaer to see what the maximum temperature you see. This will enable you to make a better viscosity choice bearing in mind the "shock loading" aspects of course
Ok, good idea.
Hi,
joecar - A good starting point is to use an IR temp redaer to see what the maximum temperature you see. This will enable you to make a better viscosity choice bearing in mind the "shock loading" aspects of course
Ok, good idea.
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