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**WorkinLonghorn** · 06-05-2023, 02:19 PM

Is this a mistake? I read somewhere that lube oil for diesel engines was the way to go. Got a good deal on some 15/40 (for diesels) at Costco. Just changed the oil this morning and got to thinking maybe that is too thin. My original Owner's Manual says to use 20/40 (or straight 30wt) in the hottest climate, IE. here in L.A. Oil has come a long way since '69 so it should be good right? This is a new GM stock replacement crate motor. -BA

06-05-2023, 02:19 PM	#1
WorkinLonghorn Senior Member Join Date: Dec 2006 Location: Studio City, Calif. Posts: 2,861	Question about oil viscosity Is this a mistake? I read somewhere that lube oil for diesel engines was the way to go. Got a good deal on some 15/40 (for diesels) at Costco. Just changed the oil this morning and got to thinking maybe that is too thin. My original Owner's Manual says to use 20/40 (or straight 30wt) in the hottest climate, IE. here in L.A. Oil has come a long way since '69 so it should be good right? This is a new GM stock replacement crate motor. -BA __________________ '69 GMC C2500 Custom Camper, 8 1/2' bed, New GM 350, NP 435 Close Ratio 4spd. Trans., 3.73 Dana-60 open.Camper and Trailer wiring, PS, PB, AC, tach , three gas tanks, 2nd owner, Work-Truck supreme. Best $300 I ever spent.