Quote:
Originally Posted by OldGuy
I'm preparing for my 1st Z oil change at 1200 miles. I'm going to use regular oil for her oil changes until 10,000 mi. The Nissan Owner's Manual prescribes 5 W30. At the same time, I'm preparing to take my Miata out of winter storage and change its oil. Its owner's manual says if outside temps are mostly over 40 degrees F and essentially summer-like, 10 W 30 should be used, 5W30 for climates offering 40 defree F and colder temperatures. My Z will enjoy temperatures over 40 degrees during this oil use period, as summer is one the way. 80 and 90 degrees will happen. I plan to obey the Nissan Owner's Manual and use 5/30 but the Mazda book does provide sensible guidance in distinguishing between warmer and cooler climates when selecting viscosity. Could someone with more mechanical knowledge than I (which would be just about anyone) please clarify this for me.
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Below is some follow-up writing I've found on the subject. Now, I'm more confused than ever:
Is there a disadvantage to using an oil that flows better when cold, i.e. 5W30 versus 10W30?
Sometimes, but usually not. The crux of the issue is this: the bigger the difference between the cold oil viscosity and the hot oil viscosity, the more the volume of viscosity modifiers and the less the volume of base stock. If you are good about following the manufacturer's recommended oil change interval then stick with the 5W30 if that is the preferred oil for your vehicle, even if 10W30 is acceptable in warmer climates. Older cars may specify 10W30 only. This is because they need a little more viscosity when cold to keep a protective film on the cylinder walls. There have been instances where the larger amount of viscosity modifiers that are present in 5W30 have broken down due to excessive heat and have left carbon deposits on the valves, but this is extremely rare. The proper fix would be to reduce the excessive heat, but the workaround was to use an oil with less viscosity modifiers.
Why do many oil change places, even dealerships, use 10W30 instead of 5W30, even when 5W30 is preferred?
According to
Car Talk. Car tips, advice, and troubleshooting. (see link in the references section), as well as many mechanics who have posted on usenet, 10W30 is the closest thing to a one size fits all oil. Many older vehicles need 10W30, and most newer vehicles are okay with it in warmer climates. Since many garages don't want to have multiple tanks of bulk oil they choose to carry only 10W30. The advice that Tom & Ray give is correct, 'it would not be a disaster if you used 10W30, but given a choice, go with the manufacturer's recommendation and use the 5W30.'