Using 80w-90 gear lube instead of 75w-90 in rear diff.

Midwestspecial

Original poster
Member
Jan 23, 2012
3
hey everyone, I recently changed my rear diff fluid and instead of researching the required fluid on my own I trusted the employee at the auto parts store to tell me what fluid to use. I ended up changing the rear diff with regular valvolin 80w-90 fluid instead of the synthetic 75w-90. Is this going to be a proble? 05 TB LS 4x4 with 93K miles on it. Old fluid was pretty dirty and probably had never been changed before. Thanks.
 

Wyle

Member
Dec 4, 2011
200
Define "problem". The different grade probably won't be a big deal, but I doubt the conventional lube will hold up as well as a synthetic (as specified in the Owners Manual). The big unknown is now the service interval with conventional 80w-90?! 100k miles? 50k miles? 10k miles?

I'd go back to the the auto parts store with receipt and Owners Manual in hand and insist that they correct the mistake. Worst they can do is say no.

If it were me, I'd keep gear lube on my shopping list and find a nice spring afternoon to crawl back under there for an hour. Cheap peace of mind for knowing it should go another 100k miles, IMHO.
 

Wooluf1952

Member
Nov 20, 2011
2,663
Milwaukee, Wisconsin
For the 2003 there is nothing listed about changing the fluid at any set time or mileage. Just check and add as needed.

Many members go with the 50k miles. Especially the off-roaders.

The 80w-90 shouldn't be a problem, but it should be synthetic.
 

Bartonmd

Member
Nov 20, 2011
545
There will be very slightly more windage losses (for lack of a better term) from the heavier fluid, but from it not being synthetic, you'll have pretty good losses before it warms up, especially in the winter...

I know I put regular dino gear oil in my Cummins, and when it's really cold out, I can push in the clutch and put the thing in neutral, coasting, and I slow down MUCH faster than when everything's warmed up... Not the case in the TB, with the synthetic...

Mike
 

Midwestspecial

Original poster
Member
Jan 23, 2012
3
thanks for the replies. I don't do any offroading and am planning on changing it again after 30K miles anway.
 

tblazerdude

Member
Dec 4, 2011
321
The main difference between 80w90 and 75w90 is the synthetic tag. The oil weight is not a noticeable difference, most if not all 75w90's are synthetic or synthetic blends. 80w90's are dino oil. I would think your oil change interval would be reduced by half, so 50k miles instead of 100k. 80w90 should be safe to use, and you won't notice a difference. I always like to point out that I found my front diff EMPTY with no signs of leakage... so I like to check my front diff every oil change.
 

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