Curious... what do some of you think about going to a thicker viscosity oil for the rear diff? Assuming moderate temps and moderate towing duties... I can't see what the disadvantage would be leaving 75w90 to 85w140 fully synthetic? or am I missing something? thanks
Royal Purple 85w-140 in rear differential
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You stand to lose a very small amount of gas mileage, but there's really no disadvantage to going to a thicker viscosity and it's mainly a benefit if you don't care about the small mpg loss.
Originally Posted By: qdeezie
You stand to lose a very small amount of gas mileage, but there's really no disadvantage to going to a thicker viscosity and it's mainly a benefit if you don't care about the small mpg loss.
Right, the guy who sold me the Mag Hytec rear differential cover told me that the reason GM spec's thinner fluids is mainly for milage reasons, and that to get the best protection I should go to MaxGear (85w140) RP... But at $16.99 a quart, and 8 quarts capacity, that's $120 worth of oil, so I want to be sure there are no harmful side effects to the gears themselves.. doesn't seem like there should be, with temps here above 15F usually and into the 40's thru 90's mostly..
You stand to lose a very small amount of gas mileage, but there's really no disadvantage to going to a thicker viscosity and it's mainly a benefit if you don't care about the small mpg loss.
Right, the guy who sold me the Mag Hytec rear differential cover told me that the reason GM spec's thinner fluids is mainly for milage reasons, and that to get the best protection I should go to MaxGear (85w140) RP... But at $16.99 a quart, and 8 quarts capacity, that's $120 worth of oil, so I want to be sure there are no harmful side effects to the gears themselves.. doesn't seem like there should be, with temps here above 15F usually and into the 40's thru 90's mostly..
If you're already increasing capacity and cooling with a MagHytec, and your location isn't the Arizona desert, you probably don't need to use an 85w140.
Stick with a 75w110 or 75w140. The 75w's will give you the improved flow that you need. 85w will be thicker than molasses when cold out.
Stick with a 75w110 or 75w140. The 75w's will give you the improved flow that you need. 85w will be thicker than molasses when cold out.
Originally Posted By: unDummy
85w will be thicker than molasses when cold out.
cold being what? like 32F or are we talking in the -(F) ranges? Cause here in Portland, it's rarely colder than 15F in the worse part of winter.
thanks in advance.
85w will be thicker than molasses when cold out.
cold being what? like 32F or are we talking in the -(F) ranges? Cause here in Portland, it's rarely colder than 15F in the worse part of winter.
thanks in advance.
I'm thinking below 70F cold.
http://royalpurple.com/prod-pdfs/max-gear-ps.pdf
I also recommend thicker for gear oils since increased capacity/cooling isn't available for all. Since you addressed capacity/cooling with the mag hytec, I'd just stick with the 75w90.
http://royalpurple.com/prod-pdfs/max-gear-ps.pdf
I also recommend thicker for gear oils since increased capacity/cooling isn't available for all. Since you addressed capacity/cooling with the mag hytec, I'd just stick with the 75w90.
I have a mag-hytec cover on my silverado. I got to thinking though, aluminum dissipates heat better than steel, but the stock cover is very thin steel and the M-H is very thick aluminum. Maybe most of the cooling effects are from the extra oil capacity. Just thinking out loud.
Originally Posted By: hisilver
I have a mag-hytec cover on my silverado. I got to thinking though, aluminum dissipates heat better than steel, but the stock cover is very thin steel and the M-H is very thick aluminum. Maybe most of the cooling effects are from the extra oil capacity. Just thinking out loud.
I think the ribbed design creates far more "surface area" for heat to dissipate, combined with the larger capacity and the nice magnetic dip stick, it's the best $200 I can think of to protect the AAM1150 for long, long service!
BTW... I talked to two different rear end shops and both seem to think that unless I live where temps are below 0F, that 85/140 synthetic would provide the best protection, as a minor cost to fuel efficiency.
I have a mag-hytec cover on my silverado. I got to thinking though, aluminum dissipates heat better than steel, but the stock cover is very thin steel and the M-H is very thick aluminum. Maybe most of the cooling effects are from the extra oil capacity. Just thinking out loud.
I think the ribbed design creates far more "surface area" for heat to dissipate, combined with the larger capacity and the nice magnetic dip stick, it's the best $200 I can think of to protect the AAM1150 for long, long service!
BTW... I talked to two different rear end shops and both seem to think that unless I live where temps are below 0F, that 85/140 synthetic would provide the best protection, as a minor cost to fuel efficiency.
80W140 would be superior to 85W140 even at 0F (-17.8C). the low temp spec for 80W is 150000cP@ -26C.; for 85W it's at -12C (+10F). 150000cP is thick!!
Why not use 80W140
http://www.mobil.com/USA-English/Lubes/P...90_80W-140.aspx
it is easy to find.
I wouldn't use 85Wxx unless I lived in a tropical or subtropical climate.
Charlie
Why not use 80W140
http://www.mobil.com/USA-English/Lubes/P...90_80W-140.aspx
it is easy to find.
I wouldn't use 85Wxx unless I lived in a tropical or subtropical climate.
Charlie
Originally Posted By: m37charlie
80W140 would be superior to 85W140 even at 0F (-17.8C). the low temp spec for 80W is 150000cP@ -26C.; for 85W it's at -12C (+10F). 150000cP is thick!!
Why not use 80W140
http://www.mobil.com/USA-English/Lubes/P...90_80W-140.aspx
it is easy to find.
I wouldn't use 85Wxx unless I lived in a tropical or subtropical climate.
Charlie
Cause I want to stick with RP... I've heard a lot of good about them from people around here at the local shops.. Maybe I'll look at the 80w90 by RP. I wonder why the 140 isn't as good as the 90 .. Why do they even make a 140?
80W140 would be superior to 85W140 even at 0F (-17.8C). the low temp spec for 80W is 150000cP@ -26C.; for 85W it's at -12C (+10F). 150000cP is thick!!
Why not use 80W140
http://www.mobil.com/USA-English/Lubes/P...90_80W-140.aspx
it is easy to find.
I wouldn't use 85Wxx unless I lived in a tropical or subtropical climate.
Charlie
Cause I want to stick with RP... I've heard a lot of good about them from people around here at the local shops.. Maybe I'll look at the 80w90 by RP. I wonder why the 140 isn't as good as the 90 .. Why do they even make a 140?
btw... with gear oil, is the 2nd number (the 140) rated the same as with motor oil? i.e. the weight at 210 Degrees? or is that at a cooler temp? Cause I imagine operating temps of a rear diff are far lower than 210 degrees, even when doing heavy towing, right?
Originally Posted By: PDX2500HD
btw... with gear oil, is the 2nd number (the 140) rated the same as with motor oil? i.e. the weight at 210 Degrees? or is that at a cooler temp? Cause I imagine operating temps of a rear diff are far lower than 210 degrees, even when doing heavy towing, right?
The viscosity temp ranges of gear oils are in a chart at the front of this site. Yes, they are at 100C. For example, 90 gear oil is slightly thicker than 40 engine oil.
And yes, diffs can get FAR warmer than 100C. In Australia my rear diff was the hottest fluid at 200F.(95C) - lucky! I've heard of 250-275F. when towing in pickups! That's why synthetics are so desirable for diffs.
Charlie
btw... with gear oil, is the 2nd number (the 140) rated the same as with motor oil? i.e. the weight at 210 Degrees? or is that at a cooler temp? Cause I imagine operating temps of a rear diff are far lower than 210 degrees, even when doing heavy towing, right?
The viscosity temp ranges of gear oils are in a chart at the front of this site. Yes, they are at 100C. For example, 90 gear oil is slightly thicker than 40 engine oil.
And yes, diffs can get FAR warmer than 100C. In Australia my rear diff was the hottest fluid at 200F.(95C) - lucky! I've heard of 250-275F. when towing in pickups! That's why synthetics are so desirable for diffs.
Charlie
I've been running diff oil temp gauges for years on my trucks and have based viscosity choices on the operating oil temps.
My way of thinking is to stay within the grade 90 viscosity (13.5cSt minimum) at the highest temp regularly seen. Almost never do they exceed the 210F viscosity rating for the grade, and when they do it's not by much and only for a short period.
Other people may see higher temps and need the protection of a 140 grade. IIRC, a 140 grade drops into the viscosity range of a 90 grade with oil temps in the 250F area. Still, I'm not afraid to let the additives work for me during a short spurts over 210F. I wouldn't tow coast to coast at 260F with a 90 grade, but I wouldn't be afraid to let it go that high for a few minutes going uphill.
The newer truck is rated for a 75W140 synthetic, but I have to run a non-synthetic because of the type of limited slip used. Plus, I run a 90 grade (80W90) because oil temps run so low, even when towing and I'll take all the fuel economy gains I can get. Both trucks have Mag-Hytec covers and they knock at least 15F off the higher temps (more on cooler days), so that's factored in.
IMO, if you use some means to cool the oil, verifying the temps, you can drop grade and benefit from the lower drag and increased mpg that comes from a lighter gear oil, whether it's synthetic or mineral.
My way of thinking is to stay within the grade 90 viscosity (13.5cSt minimum) at the highest temp regularly seen. Almost never do they exceed the 210F viscosity rating for the grade, and when they do it's not by much and only for a short period.
Other people may see higher temps and need the protection of a 140 grade. IIRC, a 140 grade drops into the viscosity range of a 90 grade with oil temps in the 250F area. Still, I'm not afraid to let the additives work for me during a short spurts over 210F. I wouldn't tow coast to coast at 260F with a 90 grade, but I wouldn't be afraid to let it go that high for a few minutes going uphill.
The newer truck is rated for a 75W140 synthetic, but I have to run a non-synthetic because of the type of limited slip used. Plus, I run a 90 grade (80W90) because oil temps run so low, even when towing and I'll take all the fuel economy gains I can get. Both trucks have Mag-Hytec covers and they knock at least 15F off the higher temps (more on cooler days), so that's factored in.
IMO, if you use some means to cool the oil, verifying the temps, you can drop grade and benefit from the lower drag and increased mpg that comes from a lighter gear oil, whether it's synthetic or mineral.
PDX2500HD,
I think you're fine with a 75W-90 synthetic in your application in Oregon ... unless you are pushing the limits of the machine or the diff ... and you said moderate duty in your first post.
Don't forget, you will be losing about the same amount of power along with fuel economy with the thickest oils. The trend in lubrication for the past decade and a half is to go thinner and reap the rewards of reduced drag. With the excellent add-packs in many oils these days, we're seeing very low wear in UOAs as well.
If you are at all torn, I would split the difference and go with Amsoil 75W-110. I know you said you wanted to try RP but I think you're using some of the best stuff available with the Schaeffer you have listed in your signature. You can pay more, but I doubt you'll see an improvement. Going for extended oil drains?
FYI, good viscosity chart you can download:
http://i229.photobucket.com/albums/ee149/BrorJace/Miscellaneous/viscositychart3.gif
I think you're fine with a 75W-90 synthetic in your application in Oregon ... unless you are pushing the limits of the machine or the diff ... and you said moderate duty in your first post.
Don't forget, you will be losing about the same amount of power along with fuel economy with the thickest oils. The trend in lubrication for the past decade and a half is to go thinner and reap the rewards of reduced drag. With the excellent add-packs in many oils these days, we're seeing very low wear in UOAs as well.
If you are at all torn, I would split the difference and go with Amsoil 75W-110. I know you said you wanted to try RP but I think you're using some of the best stuff available with the Schaeffer you have listed in your signature. You can pay more, but I doubt you'll see an improvement. Going for extended oil drains?
FYI, good viscosity chart you can download:
http://i229.photobucket.com/albums/ee149/BrorJace/Miscellaneous/viscositychart3.gif
Originally Posted By: Bror Jace
PDX2500HD,
I think you're fine with a 75W-90 synthetic in your application in Oregon ... unless you are pushing the limits of the machine or the diff ... and you said moderate duty in your first post.
Don't forget, you will be losing about the same amount of power along with fuel economy with the thickest oils. The trend in lubrication for the past decade and a half is to go thinner and reap the rewards of reduced drag. With the excellent add-packs in many oils these days, we're seeing very low wear in UOAs as well.
If you are at all torn, I would split the difference and go with Amsoil 75W-110. I know you said you wanted to try RP but I think you're using some of the best stuff available with the Schaeffer you have listed in your signature. You can pay more, but I doubt you'll see an improvement. Going for extended oil drains?
FYI, good viscosity chart you can download:
http://i229.photobucket.com/albums/ee149/BrorJace/Miscellaneous/viscositychart3.gif
Yeah, I use Schaeffer 9000 in the engine, and I plan to go about 10K with it max.. filter changes every 5K. TranSynd in the Allison as per their recommendation.. As for the differential, I was "advised" to use the RP 85w-140 by the guys who installed my Mag Hy-tec cover...
PDX2500HD,
I think you're fine with a 75W-90 synthetic in your application in Oregon ... unless you are pushing the limits of the machine or the diff ... and you said moderate duty in your first post.
Don't forget, you will be losing about the same amount of power along with fuel economy with the thickest oils. The trend in lubrication for the past decade and a half is to go thinner and reap the rewards of reduced drag. With the excellent add-packs in many oils these days, we're seeing very low wear in UOAs as well.
If you are at all torn, I would split the difference and go with Amsoil 75W-110. I know you said you wanted to try RP but I think you're using some of the best stuff available with the Schaeffer you have listed in your signature. You can pay more, but I doubt you'll see an improvement. Going for extended oil drains?
FYI, good viscosity chart you can download:
http://i229.photobucket.com/albums/ee149/BrorJace/Miscellaneous/viscositychart3.gif
Yeah, I use Schaeffer 9000 in the engine, and I plan to go about 10K with it max.. filter changes every 5K. TranSynd in the Allison as per their recommendation.. As for the differential, I was "advised" to use the RP 85w-140 by the guys who installed my Mag Hy-tec cover...
With all due respect to the diff cover installers, I doubt they know what I stated in previous post re 85W140 being virtually solid at +10F. That is not good for your bearings!!!Or the R&P for that matter. You don't live in the tropics.
I'll weigh in for the Amsoil 75W110 (if you want something thicker than 75W90), or at the thickest, a synthetic 80W140 like Delvac, which at least stays liquid down to -15F. Jim Allen made some excellent points in his post: you want a lubricant that is as thick as 90@100C. at YOUR running temp.
You appear to know the benefits of 5W40 in the engine. running 85W140 in the diff in Oregon is like running 20W50 in the engine!
Charlie
I'll weigh in for the Amsoil 75W110 (if you want something thicker than 75W90), or at the thickest, a synthetic 80W140 like Delvac, which at least stays liquid down to -15F. Jim Allen made some excellent points in his post: you want a lubricant that is as thick as 90@100C. at YOUR running temp.
You appear to know the benefits of 5W40 in the engine. running 85W140 in the diff in Oregon is like running 20W50 in the engine!
Charlie
PDX2500HD,
You could also e-mail Royal Purple and see which of their oils they would recommend in your application. Just be specific about what you have, what you are doing with it and your expected oil drain interval.
I'm betting they recommend 75W-90 Max Gear.
You could also e-mail Royal Purple and see which of their oils they would recommend in your application. Just be specific about what you have, what you are doing with it and your expected oil drain interval.
I'm betting they recommend 75W-90 Max Gear.
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