Q: I took our new car in for its first 5,000-mile service at the dealership and was admonished by the service advisor for using regular gasoline. The owner’s manual says premium fuel is recommended, but the car has been running just fine using regular gasoline. The service writer tells me that deposits could be a problem since this car has fuel injection. Can you offer any insight into this issue?
A: Your service advisor has raised two issues. The first centers on fuel grades, and here, there is good news. Many cars optimized to burn premium gasoline can also run well on regular-grade fuel. Though this practice most likely will slightly reduce performance and fuel economy, few drivers will notice the difference. Your car is apparently one of these vehicles, which explains why the owner’s manual recommends, rather than requires, the use of premium fuel. Under these circumstances, you should be able to use regular gasoline and, as a result, save about 20 cents a gallon.
As for deposits, gasoline usually contains detergents that can help keep intake valves clean in many older and newer fuel-injected engines. If you choose a regular-grade gasoline with these detergents, you should be okay.
An increasing number of newer engines, however, use direct fuel injection, which complicates this discussion. Depending on the make and model of the car you own, it is possible that you have such an engine. Without getting too technical, direct injection means that the detergents in the gasoline will have little if any effect on intake valve cleanliness. As a result, a few of these direct-injection engines have suffered from drivability problems, lack of power and hard starting once carbon deposits form on the backs of the intake valves. Removing these deposits is costly, and since they take time to form, the need for repairs will probably become apparent only after the vehicle manufacturer’s warranty has expired.
Some technicians believe that impurities from the combustion process in these direct-injection engines are at fault. These harmful byproducts can react with engine oil additives and form substances that, when sucked into the engine through the positive crankcase ventilation (PCV) system, end up on the intake valves. Your best defense would be to use quality fuels and scrupulously follow the automaker’s maintenance and oil change recommendations.
This article originally appeared in the November/December 2017 issue of AAA World.