Under the Hood: High performance engines require premium grade fuel

McClatchy-Tribune Information Services

June 3, 2019

Q: I have a 2015 Infinity Q70. I use premium gas. Do I have to? Is it recommended or is it a marketing trick to pay more? I have always driven Infinitis and have paid for premium. Is it worth it?

They say an Infiniti will run forever if you change the oil regularly. I donít need synthetic oil. Just regular oil is fine. Correct? But whatís the interval? I usually go to Jiffy Lube every 3,000 miles. Good practice?

ó Joe in Chicago

A: Your Infiniti Q70 requires premium grade fuel. Checking the filler neck/gas door for a label can confirm this. Many vehicles with high performance engines require premium grade fuel because of its higher octane, which mitigates detonation, a violent form of abnormal combustion. Significant pressure, heat and stress occur when fuel explodes rather than burns in a controlled fashion.

Some car makers merely recommend premium fuel. In this case the engineís requirements are not as high, and the management system is capable of tuning ignition timing and other functions to tolerate lesser grade fuel. If driven under high temperatures or stressful conditions, such as climbing over a mountain pass during the heat of summer, I would absolutely go with the higher grade recommended fuel. If a vehicle doesnít specify premium fuel is needed, and there are no issues with pre-ignition or detonation, using it is a waste of money.

Regarding your oil change question, the Infiniti engine on your Q70 employs special friction reducing coatings on certain parts and a highly sophisticated valve train that benefit from using top-notch oil.

Nissan recommends their branded ($13-ish per quart) engine oil that contains an ester additive and some other high-tech friction reducing tricks. There is considerable debate on whether a good synthetic oil might do just as well at less cost. Infinity recommends changing oil on your Q70 every six months or 5,000 miles.

What really matters is your driving habits. Extreme cold weather operation, short run times, lots of idling in traffic at higher temperatures, demanding high temperature conditions/towing, and driving in dusty conditions bring down the recommended oil change interval possibly as low as 3,000 miles. Easier conditions and long run times could make a 8,000- to 10,000-mile oil change reasonable. Iím thinking: buy a five quart jug of Mobil 1 extended performance synthetic oil for $30 or $35 and bring it to your shop every 5,000 to 6,000 miles.