Very bad looking diff oil.

Joined
Jul 28, 2009
Messages
86
Location
Spain
Hello. I have been flushing my front differential that hadn't been serviced in the last 15000 km (9000 miles), and the oil coming out looks horrible. The service interval is about 20000 miles I think, but I replaced it earlier cause I made some water crossings, but I expected it to look better anyway. I could not take the bolt out of the rear differential so I can not compare. This is how it looks: About the new oil, I put in SAE EP (Extreme pressure) 90 GL-5. The FSM says over -18ºC SAE 90 GL-5 is ok, but it doesn't mention if the extreme pressure variant is ok or not.
 

djb

Joined
Jan 16, 2006
Messages
784
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Los Gatos CA
The GL-5 rating means that it has a high level of EP additives, so I think that the "EP" part of the oil description was redundant. Listing the brand would have conveyed much more information. Including the type of vehicle and transmission would have been useful as well.
 
Joined
Apr 13, 2009
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3,402
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Iowa
Looks pretty dark for 9000 miles, but if you drive it hard, maybe it oxidized faster than usual. I dunno.
 

PT1

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Feb 6, 2007
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5,746
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near the mistake
Looks like the oil on my AWD Yukon Denali right before the carrier bearings failed. Stick a magnet in it and see what you get. My Denali front diff burned up the GM 100,000 mile 75w90 GL5 synthetic lubricant in 10,000 miles. That oil is definitely oxidized due to heat.
 
Last edited:

ecco123

Thread starter
Joined
Jul 28, 2009
Messages
86
Location
Spain
Thank you guys. Well, now that you mention about driving hard and heat. Half of those 9000 miles have been done in Africa, on expedition trips, with the truck loaded, and sometimes driven really hard on sand. The outside temperatures have been pretty high sometimes but not extreme cause I always go to Africa on Winter (90-100ºF). I should have mentioned these factors before. Anyway, I just flushed the transfer case oil as well, that had the same mileage and have been used in the same condtions and it looked perfect, just like new. When you say stick a Magnet on it, you mean in the old oil don't you?
 
Last edited:
Joined
Dec 11, 2006
Messages
77
Location
USA
Africa is hot in any case! Your description of driving definitely falls into the severe service category. Might consider a synthetic 75w140 GL5. It looks like your gear lube was the victim of "thermal runaway."
 
Joined
Feb 1, 2003
Messages
8,756
Location
RI
Definitely toasted. Upgrade to a full synthetic and 75w140 is an excellent choice with those weather conditions.
 
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