lightest/thinest 75w-90 gear oil

[thereed]

The gear oil is for my '07 chevy colorado crew cab 2.9 4cy 2wd w/g80 locking diff. In the past I've used amsoil sever gear, mobil syn, and most resent is smittys super s syn all is the factory recomended 75w-90.

It only takes a couple of qts. of fluid so the price isnt much of a factor in my selection due to all of the syn fluids being roughly a few dollars apart. I'm looking for the lightest/thinest for a possible fuel mileage increase, considering that a 75-90 is = to a 10w40-20w50 range. Am i correct in thinking that a thick(20w-50) vs a thin(10W-40)gear oil could produce a measureable fuel use difference?

Should I just be looking at the Kinematic Viscosity, or is the Brookfield Viscosity more important? The lower the # the better, correct?

 

[dparm]

Motul Gear 300 is definitely on the lighter side when looking at the KVs. Also has a super-high VI of 222.


Viscosity at 40°C (104°F) ASTM D445 72.6 mm²/s
Viscosity at 100°C (212°F) ASTM D445 15.2 mm²/s

 

[Loobed]

Look at Klotz Lube: http://klotzlube.com/products.asp?cat=3&pg=3

They have a lot of different grade gear oils.

here is 75w-55 http://klotzlube.com/techsheet.asp?ID=22&submit2=View

 

[Colt45ws]

Something you could also try is filling to the bottom end of specs. Like my axle specs 1/4" to 1/2" under the fill hole. Filling to the minimum mark would net a bit of a reduction in drag over the maximum mark or even more if you are like a lot of people and fill until it pours out the hole.
I know redline makes a 75w85. You could blend up a custom mix with that and some of their 75w90 to yield something on the bottom end of the 90 scale.

 

[Doug Hillary]

Hi,
please do NOT underfill your differential(s). This can lead to serious issues - it is an unwise practice!

 

[Colt45ws]

I didnt say that.
Manufacturers have ranges of acceptable lubricant level.. I was simply suggesting running on the low side of the ACCEPTABLE range would yield a slight decrease in drag over the full mark.
This does run a slightly higher risk of running low if its starts leaking, but Im assuming that people on a forum about oil would be aware enough to catch it before it becomes a serious problem..

 

[SubLGT]

Originally Posted By: thereed
...........Should I just be looking at the Kinematic Viscosity ?.......


Yes. look for the lowest KV, and the highest viscosity index. IIRC, Dparm listed these specs in another thread for a lot of gear lubes. Also look for the GL5 rating.

 

[m37charlie]

Don't use a 75W85 if the specs call for a 75W90. A new ring and pinion gear and bearings aren't cheap, and the cost is some indication how much natural resources are used to make the parts.
By all means go ahead and spend $20/L for synthetic ester Motul 300 gear oil if you want to. Although I estimate your fuel consumption will drop 0.5% at the MOST relative to a typical PAO synthetic gear oil like Delvac Synthetic Gear Oil 75W90.
http://www.mobil.com/USA-English/Lubes/P...90_80W-140.aspx

Charlie

 

[Loobed]

I tried different 75w-90 gear oils in my truck and found no MPG gains that were worthwhile. A small vehicle may see and improvement in MPG. I have not tried Motul.

 

[Ken2]

Quote:
Am i correct in thinking that a thick(20w-50) vs a thin(10W-40)gear oil could produce a measureable fuel use difference?
no. Probably not measurable outside of a lab. A couple of psi underinflation in your tires due to cold weather or a head wind will have more effect. If you need to change the gear oil, OK. If you're trying to save money, you'll never save enough gas to pay for the new gear oil.

 

[Doug Hillary]

Hi,
Colt45ws - I didn't say that YOU SAID to under fill the diff

Originally Posted By: Colt45ws
I didnt say that.
Manufacturers have ranges of acceptable lubricant level.. I was simply suggesting running on the low side of the ACCEPTABLE range would yield a slight decrease in drag over the full mark.
This does run a slightly higher risk of running low if its starts leaking, but Im assuming that people on a forum about oil would be aware enough to catch it before it becomes a serious problem..


It is best to stay with the Manufacturer's intended lubricant levels in both gearboxes and differentials

Use in situations where gradients are more that 10% or excessive road camber may cause operation at an acute angle can cause technical issues. This is especially so if the vehicle is under load and power (or both) or where the differentials intended operation is continued for long periods

Not everybody accessing BITOG is skilled or knowledgeable and can mis-interpret the intent of some Postings

 

[thereed]

I'm not looking to change out the gear oil I have in there now just to save some gas. I'm just planning ahead for my next change so I can start looking for a good deal. I have access to multiple auto parts stores that carry everything from Amsoil & Redline to the usual suspects like Mobil, Castrol and the SOPUS offerings. The price is actuall pretty close with all of their offerings so I figure I would get some info to make an informed decision.

I was looking at another gear oil thread and it seems like a high VI is another factor to look at. The more I learn, the more confusing it becomes for those of us with auto maint. OCD.

 

[Doug Hillary]

Hi,
thereed - IMO you would be best served by settling on one conforming lubricant and staying with it

By the way I love Portland and Oregon

 

[Garak]

What I've noticed up here, at least, is that the synthetic offerings are not much more than the conventional ones (especially in comparison to the difference between conventional and synthetic motor oil). That's why I tried synthetic this time around. Besides, the differential fluid change is messier than an oil change, so I prefer the extended interval.

 

[martinq]

Is there an oil that meets GL-5 and SAE90 that is lighter than Motul Gear 300 75w90? Is does anyone make a 70w90?

Also, is it possible to extrapolate the Brookfield -40C viscosity from the 40C and 100C numbers?

http://www.motul.com/system/product_descriptions/technical_data_sheets/106/Gear 300 75W90_GB.pdf

 

[mechtech2]

Going from the lightest to heaviest gear oil in any range will not net you measurable results.

 

[martinq]

Originally Posted By: mechtech2
Going from the lightest to heaviest gear oil in any range will not net you measurable results.

I'm not looking for measurable results. I'm looking for a GL-5 SAE90 that would out-perform or out-flow the Motul Gear 300 75w90. Something that fit into a 70w90 classification should do it.

 

[azsynthetic]

Red Line Lightweight Gear Oil 75W80 GL5

Red Line Superlight Gear Oil 70W75 GL5

 

[martinq]

Originally Posted By: azsynthetic
Red Line Lightweight Gear Oil 75W80 GL5
Red Line Superlight Gear Oil 70W75 GL5

Due to the low VI of Red Line and high VI of the Motul, Gear 300 75w90 should come out on top. BTW, the Red Line tech-sheet and website have different info for the oils. Since the tech-sheet is from 2009 I'll take the specs from the website which does not list the Superlight 70w75.

Fluid . . . 40C . . VI . . PP . -40C
=============================
RL.75w85 . 62.0 160 . -45 . 500
MG75w90 . 72.6 222 . -60 . 84 (calc'd)

According to Widmans viscosity calculator the two should intersect around 20C. The Motul is more fluid below that point.

http://www.widman.biz/English/Calculators/Graph.html

 

[martinq]

Actually, based on those numbers (and graph) shouldn't the Motul Gear 300 be spec'd as a 70w90 and not a 75w90?

70w = visc max of 150,000 at -55C
75w = visc max of 150,000 at -40C

Gear 300 shows (according the the graph) a visc of < 50,000 at -55C where Red Line 75w85 is < 300,000.