What's the best motor oil for our cars?

[SoCal LS-L]

Originally Posted by Pierre-Olivier

MOTUL 300V 10W40 for my SVX.

Hmmm, zombie thread. I will leave my mark here nonetheless.

Postcount 1UP !!

[ZMan]

Originally Posted by Pierre-Olivier

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Good Answer!

[Huskymaniac]

He probably wanted to resurrect the discussion. I agree with what dcarb said 6 years ago! After talking with people on BITOG and my mechanic, frequent oil changes are more important than the oil itself, within reason. Yes, synthetic oils have higher flash points and retain viscosity over a wider range of temperatures but they still get dirty from combustion artifacts and not all of that contamination is filtered out by the oil filter. If you drive mostly highway miles and never in harsh conditions, you probably can switch to synthetics and drive 7500 miles or even more between oil changes. Then it is worth it. If you drive in mild to harsh conditions, however, the oil will get contaminated and should be changed ever 3750 miles. For that frequency, it is a waste of money to go with synthetic motor oil. Harsh is defined as short trips, dusty roads, high or low temperatures.

Differential and tranny oils, however, are a different story. Synthetics will result in lower operating temperature and will break down slower and can result in extended fluid change durations. I, however, will be sticking with 30K mile durations and just take advantage of the other benefits of synthetics in the differentials and tranny. Also, synthetics in the differentials and tranny will improve gas mileage whereas synthetic motor oils will have little impact on gas mileage. Ester based oils like Redline are particularly good in these cases as esters are especially good at wetting metal surfaces to aid in heat transfer.

I'm not sure I agree with comments on high mileage oils. They do help in keeping the engine clean and they have seal conditioners that help keep seals from shrinking and leaking. I actually view high mileage oils as more of a preventative measure rather than a fix for existing problems. It is unlikely that they will make leaky seals stop leaking for an extended period of time but they may help keep good seals in good condition.