The current API spark ignition service category is "SL" and in process of going to "SM". Some prefer to use HD diesel engine oil (API service category CI-4), but if oil consumption is high the combustion byproducts of the higher additive concentration may reduce catalyst life.

Viscosity selection is based on ambient temperature range. Look in your owner's manual, again - in the back, specification section. My '88 owner's manual has a chart! So what is your expected range of highest and lowest cold start temperature over the year.

Oil selection is not rocket science, but ignore the advertising hype. Buy name brand oils in the proper API service category and viscosity range for your climate - whatever is on sale!

The recommended change interval is 7500 miles or one year. Just because the oil appears dirty does not mean is it not serviceable.

Duke