Mobil1 75W90 or 75W140?

Status
Not open for further replies.
Joined
Jan 28, 2003
Messages
195
Location
Colorado
I use Mobil 1 75w-140 in the front and rear axles of my '01 Cherokee. 3.55's, Dana 30 and Dana 35c. The service manual specifies "75w-140 SYNTHETIC" for severe service. -brian
 

brian

Thread starter
Joined
Jan 28, 2003
Messages
195
Location
Colorado
I have not noticed a difference in fuel economy between the 75w-90 and 75w-140. In cold weather a lot of things sap fuel economy. Like cold engine oil before it warms up. Brian
 
Joined
May 12, 2003
Messages
7,829
Location
Oklahoma
For the F150, they recommend the thicker for towing and lot's of off roading, but still use the lighter weight in the front, regardless. Based on your usage, I'd go with the lighter stuff. Might want to see if your rear end requires a FM if you have limited slip. Not sure about the Jeep's. I know Ford requires it.
 
Joined
Aug 13, 2003
Messages
203
Location
NY
BUT can you get bearing damage from using a 140wt in cold weather? I put a small bottle of the Amsoil(75W140) severe gear stuff in the freezer (0 F) and it flowed and acted exactly as honey. it was very thick and when i shook the bottle it did not splash around and make that oil sound that i have come to love [Happy]
 
Joined
May 12, 2003
Messages
7,829
Location
Oklahoma
I can't see how it would hurt it. The pinions would just get a good heavy coating of grease as the gears moved and eventually "thin" out once it gets warmed.
 

brian

Thread starter
Joined
Jan 28, 2003
Messages
195
Location
Colorado
My only complaint with Mobil 1 75w-90 was that it came out BLACK in the front and rear axles of my '01 Cherokee. 80w-90 mineral oil was darker after 1000 miles. 75w-140 retained its lighter color after 1000 miles. This was back in October. I've had the 75w-140 in all winter. No problems yet. -brian
 
Joined
May 12, 2003
Messages
7,829
Location
Oklahoma
Yeah, but color is not indicative of oil quality. Just means that the lube is doing it's job in cleaning up from the old oil and keeping all the deposits in suspension and not caked on your gears.
 
Joined
Aug 15, 2004
Messages
2,365
Location
Canada
Use 75w90. Your pocket book will thank you when you fuel economy doesn't take a dive when the temperatures drop below 32f.
 
Joined
Dec 22, 2002
Messages
4,752
Location
The Garden State
My 2002 F150 uses 75W-90 in the front diff and 75W-140 in the rear diff. The wife's 2002 Explorer uses 80W-90 in the front and 75W-140 in the rear diff. I put Schaeffer's #267 semi-synthetic 80W-90 in the front diffs of both our trucks. I had no problem this cold winter in the F-150 using Schaeffer's 80W-90 over Ford's 75W-90 front diff fluid. For the rear diff I'm going with MolaKules synthetic 75W-90 for the rear diff's. We don't tow, except maybe a 1500 lb trailer once in the blue moon. Hopefully we'll save some mpg with the 75W-90 over the factory 75W-140. Whimsey
 
Joined
Apr 17, 2004
Messages
6,677
Location
Texas Hill Country
ford specs my rear end in the 98 f150 for 75w140. I went with the royal purple because there is a dude on ebay who sells royal purple gear oil pretty cheap. It seems to be working well for me. The guy who said something about single digit temps, wouldn't the gear oil be the same thickness at 0 degrees, because the lower number is 75w?
 
Joined
Oct 11, 2002
Messages
593
Location
Pittsburgh PA
quote:
The guy who said something about single digit temps, wouldn't the gear oil be the same thickness at 0 degrees, because the lower number is 75w?
Yeah I would tend to think so. Like motor oil; 10w30, 10w40,10w60 etc are all a "10 weight" oil at Zero degrees.
 
Joined
Mar 20, 2004
Messages
4,375
Location
Camas, WA
If the vehicle is seeing 'severe service' per the guidelines I'd use the lube recommended. If you're worried about mileage or such then switch back to a lighter oil, but that'll be kind of expensive.
 
Joined
Feb 27, 2005
Messages
118
Location
Carmi, IL
I will be changing the oil in my front and rear differentials on my 2000 Grand Cherokee. Which gear oil should I use? Is there any advantage to the 75W140 over the 75W90? My driving is mostly on road, and I tow or carry heavy loads only a few times a year. Would I see any MPG difference between the two? Any other I should look at besides Mobil1? I would like to stay synthetic. Thanks!
 
Joined
Aug 13, 2003
Messages
203
Location
NY
i wondered that my self. i finally went with the 140wt but every time it hit single digits i kinda regret it... the only thing i can tell you is that Redline claims the diff in efficiency between the two viscosities is only about 0.5% (hard to believe)
 

brian

Thread starter
Joined
Jan 28, 2003
Messages
195
Location
Colorado
Color is somewhat of an idicator. Gear oil should not come out black. Since my axles have had Mobil 1 75w-90 within a few hundred miles of factory new, I do not think there was any cleaning occurring. For synthetic, 75w-140 is the standard "thick" viscosity. Brian
 
Joined
Jul 26, 2004
Messages
374
Location
Northern California (Vacaville)
quote:
Originally posted by brian: Color is somewhat of an idicator. Gear oil should not come out black. Brian
Sometimes it does, I think. According to Eaton, the new G80 locking differentials have carbon fiber plates which will discolor the oil during the break-in period. [Cheers!] Bob W.
 
Joined
Jul 20, 2004
Messages
342
Location
North Kingstown, RI
quote:
Originally posted by 1maniac:
quote:
The guy who said something about single digit temps, wouldn't the gear oil be the same thickness at 0 degrees, because the lower number is 75w?
Yeah I would tend to think so. Like motor oil; 10w30, 10w40,10w60 etc are all a "10 weight" oil at Zero degrees.

What is the spec for the first number? Isn't it 0°C?
 
Status
Not open for further replies.
Top