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Comp,
The general consensus seems to be that flat tappet engines need at least 1200 ppm of zinc dithiophosphate (aka zinc). It's hard to find such an oil in a normal retail parts store, but these should still be ok:
1) Chevron Delo 400le (non-synthetic), 15W-40, CJ-4 API rating, 1230 ppm zinc.
2) Valvoline Premium Blue (non-synthetic), 15W-40, CJ-4 API rating, 1291 ppm zinc.
I sure there are some synthetics with more than 1200 ppm of zinc and hopefully, someone else will chime in.
Hope this helps.


Shell Rotella T 5W40 synthetic is 1300+ ppm zinc. $17 per gal.

Mobil 1 15W50 synthetic is 1300+ ppm zinc. $22 per 5 qt jug.

2010 Black Challenger SE <> 3.5 V6
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