By Paul Stenquist / Originally Published June 16, 2015 / Hagerty /

Whether you have a deep personal connection to your vehicle or consider it just transportation, proper care and feeding is a smart policy. For the most part, common sense will serve as a reasonable guide in making those decisions.

Not so when it comes to fuel selection. Choosing the right octane grade involves weighing performance against cost, for example, and questions over gasoline blended with ethanol have persisted for years. While gasoline cut with ethanol can offer higher octane ratings and lower tailpipe emissions, it also carries the reputation for damaging fuel systems and other components.

American motorists began burning E10 in the late 1970s. By 2005 it had become the most commonly available blend. Today, in many areas, it’s hard to find fuel that doesn’t contain at least 10 percent ethanol. For most users, especially drivers of late-model cars, that’s not a problem, though owners of boats and chain saws have complained loudly.

The situation got more confusing in 2010, when the Environmental Protection Agency granted a waiver allowing use of gasoline containing 15 percent ethanol, or E15, for use in model year 2007 and newer light-duty motor vehicles. In 2011 the waiver was expanded to include vehicles produced since 2001. The Renewable Fuels Association, an advocacy group, applauded the decision.

Many car companies said, “Not so fast.” And the EPA specifically excluded all motorcycles, off-road and heavy-duty vehicles, and outdoor power equipment.

So what’s best for your car? Although the EPA approved to E15 blends, some automakers are still wary of it, even for 2015 models. What’s more, no automaker recommends using E15 in 2001-6 vehicles. Yet the warning sticker on the filling station’s E15 pump will tell you it’s OK use it in 2001 and newer passenger vehicles or flex-fuel vehicles, which are engineered to burn up to 85 percent ethanol.

GM has approved E15 for vehicles produced since 2012, except 2015 Chevrolet City Express, and Ford has been on board since 2013, but Chrysler doesn’t approve it for any vehicles. Toyota approved E15 for all new models for the first time this year, as did Honda.

A BMW spokesman, Thomas Plucinsky, said in a phone interview that E15 is not recommended for any of the automaker’s products. According to Mark Green’s Energy Tomorrow blog, Volvo, Subaru, Nissan and Mazda also say no to E15. For any car built after 2012, check your owner’s manual, and if E15 isn’t recommended, stay away. For any car built before 2012, stick with E10.

Why? Simply because ethanol can corrode metal parts and damage some synthetic parts. Some recent cars are made without ethanol-resistant materials.

How about that 50-year-old classic? You certainly shouldn’t fill up on E15 if your engine and fuel system are original equipment or OE replacements. Blends of E10 are nearly unavoidable, though, and can cause some deterioration and corrosion over the long haul.

Fortunately, a problem like a sticking float valve in the carburetor or a clogged fuel filter will make itself known in terms of performance problems. A 2009 test of six older automobile fuel systems that Kettering University performed for Hagerty found little damage beyond discoloration.

This article has been reproduced with the permission of the copyright holder, Hagerty. Further reproduction is prohibited without permission. Click here for more classic car stories from Hagerty.