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Re: 1969 BUICK RIVIERA
Posted to Castrol Forum on 1/24/2018 2 Replies

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GM specs a low HTHS 5W-30 for that application (1999 GM 5.7). They specifically prohibit the use of any 10W-40, 20W-50 and 15W-40. One big reason is that the low tension piston rings are sensitive to... Login to read more.

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