Vehicle is 2001 Dodge Ram, 64k miles, 2WD, Limited Slip differential. Planning on changing the differential oil. I have Pennzoil Platinum 75W-140 Limited Slip full synthetic and Castrol 80W-90 limited slip (non synthetic). The manual says 80w-90, and also says for heavy use the 75W-140 synthetic is recommended. My questions:
1) both oils say limited slip on the label, and I think they mention additives in the fine print. Is there any reason I should not trust these as having the right and proper amount of FM additive? (general rule seems to be to buy oil, buy additive, and mix, but why since they sell oil that seems to have additive already in it?).
2) I don't use the truck for heavy-duty service, but I assume I can still use the 75W-140 synthetic (unless maybe thats not really the best choice for light-duty use?). Another aspect here is -> will changing to synthetic mess up the original seals? Lead to leaks?
1) both oils say limited slip on the label, and I think they mention additives in the fine print. Is there any reason I should not trust these as having the right and proper amount of FM additive? (general rule seems to be to buy oil, buy additive, and mix, but why since they sell oil that seems to have additive already in it?).
2) I don't use the truck for heavy-duty service, but I assume I can still use the 75W-140 synthetic (unless maybe thats not really the best choice for light-duty use?). Another aspect here is -> will changing to synthetic mess up the original seals? Lead to leaks?