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0W-30 Oil Consideration
Have you ever considered that the normal operating temp on an N55 / N55 Variant is on average 228-238F pending on outside air temps and driving style. (My observations on my N55)
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Oil viscosity temps are taken at 100C or 212 F. So at 212 F the oil (30wt) is up to 12.5cst thick (max for any 30wt oil) however, your car sees 228 - 238 F just driving around town on a 50F day. Now that same oil at 230 F -- gets almost as thin as a 20wt oil and at 240F (summer driving) the oil has a hard time providing the film and bearing strength to keep your car protected. Plus you have a car that is Direct Injected where fuel dilution can further lower the viscosity.
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So - for winter the 0W-30 may be the right oil -- but a 40WT just may be the better choice for summer. I am thinking 0W-40 or 5W-40 year around depending on where you live unless fuel economy is a top criteria.
A 12cst thick oil at operating temp is optimal for the N55 and it is interesting that at 230F a 40Wt oil (on average) runs a viscosity of 12cst.
Cheers,
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