1986 international s1900 w/ dana spicer international ra47 rear axle

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3
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CA
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international recommends an 85w140 but I cant find a full synthetic at that exact weight. would there be any detriment in using mobil1 75w140 instead? as far as I understand the 140 is the main number the other is flow rate while cold which may help it during winter a bit or is there more to the cold weight than that? would you recommend mobil1 synthetic or some other brand for this rear axle and diff? Thank You ahead of time for your suggestions and insights!
 
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2,526
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wv
Originally Posted by Autodiculous
international recommends an 85w140 but I cant find a full synthetic at that exact weight. would there be any detriment in using mobil1 75w140 instead? as far as I understand the 140 is the main number the other is flow rate while cold which may help it during winter a bit or is there more to the cold weight than that? would you recommend mobil1 synthetic or some other brand for this rear axle and diff? Thank You ahead of time for your suggestions and insights!
Why do you want/need a full synthetic? Are you doing long hauls and changing every 100K miles? I wouldnt want to spend a bunch of money on synthetic rear diff oils and have a wheel seal blow, and have to chase down a synthetic. Your 1986 S1900 will not last any longer or run any better on full synthetics.. Put your efforts towards good oil filters, fuel filters and air filters. Check fluids often.. run it and keep an eye on it.
 
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1,063
Location
Northern, NY
Unless you are operating the truck in cold weather or are looking for the extended drain capabilities of a synthetic, 85w-140 will work just fine. 80w-140 synthetic is available at most truck stops or oil distributors if you decide to go that route. Do not forget the cooling system when servicing your truck.
 

CT8

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15,408
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Idaho
Lots of referring to winter.where in California do you live / operate the vehicle in? You have a 1986 truck and what are you worrying about ?
 
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