1991 GMC Sonoma Engine oil

1991 GMC SONOMA
120,000 MILES • 6 CYL • 2WD • AUTOMATIC
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MIGUEL LOPEZ
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I have a GMC Sonoma 1991 4x2 4.3L, V6. I changed the engine few years ago, but "new" engine has 120000 miles already. Is working fine, I take good care of it. My question is: What kind of oil should I use in this high mileage engine? I have been using 10-40 all the time but wonder if I should change to another oil. Can I use synthetic or do you think it's not recomended in this old car? I live in Florida, hot weather. Thank you very much for your help.
Nov 22, 2009 at 11:09 AM
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KASEKENNY
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You don't need to do anything specific as the recommended oil will be fine.

https://www.2carpros.com/articles/how-to-change-engine-oil-and-filter

If you want to use synthetic, then that is fine. It will give a little better protection but the nice thing is it will last longer and so you can spread out the oil chances a little more.

I am attaching the OEM spec below and if it were me, I would stick with this weight and if you want to use a high mileage additive then that will work as well.
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Jan 8, 2022 at 9:23 AM