Quote:
Originally Posted by Mystic ZR-1
10w40, 15w50 etc...
How come GM said 10w30?
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At the time the LT5 was introduced, phosphorus and zinc in the API SG and later the SH was 1200/1300 respectively (
C-link).
If there is a synthetic 10/30 with the phos./zinc at the 1200/1300 levels, then it might rise to the top of the recommendation list for today's LT5 oils However, shopping around, there doesn't appear to be a 10/30 that does, or if there is, it isn't exactly advertised very aggressively, apparently.
So, reasonable substitutes are the AMO 10/40 (the 10W... part is the key with regard to cold viscosity) with 1200/1300 and Mobil 1 15/50 also has the same ppm of the good stuff. And too, the Mobil 1 High Mileage 10/30 comes close and might be fine too (and is what I bought for Jim and Nancy's car when the oil filter sprung a leak on the Mountain Run.)
Since I don't drive much in winter due to the salt, 10/40 is fine for summer, I recon. And, when I buy it by the case, the price for AMO 10/40 gets down around $7/qt, changed every-other year (under 5000 miles as a rule).
P.