I just bought my first project car after graduating from college—a 1970 Ford Thunderbird. It was running fine for a while, but then I started noticing acceleration issues, and now it won’t start. I recently found out that older cars shouldn’t use gas with ethanol, but I’ve been filling it with premium gas that has some ethanol (not E85) for a few months. Did I mess something up? What should I check or do next?
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Did the car sit unused for a while after you put the ethanol gas in? If so, it might’ve gummed up the carburetor. You’ll need to take the carb apart, clean everything thoroughly, and make sure all the tiny openings are clear.
It’s generally okay to use gas with ethanol in older cars (since that’s what most gas stations sell now), but if you’re planning to let the car sit for a while, you should add a fuel stabilizer or drain the carburetor.
If the carb isn’t the issue, you might want to check the spark plugs, distributor cap, and rotor. Start with the carb, though—it’s the most likely culprit.
@Skyler
Ethanol absorbs water, which can cause problems if it’s been sitting in the fuel system for too long.
@Skyler
Ethanol can also eat through old rubber parts and hoses, so you might want to check those too.
Don’t forget to check the fuel filter. If it’s clogged, it could explain the power loss and starting issues.
Modern gas with ethanol works fine in carbureted engines as long as you don’t let the car sit unused for long periods. I run E15 in my old carbureted 350, and it’s been fine even after sitting for a couple of months.
That said, it’s a 1970 car—there could be all sorts of issues. When you start driving an old car regularly again, stuff will break. It’s part of the process, but once you fix the initial problems, it’ll be more reliable.
E10 or E15 won’t damage your car. E85 could harm older rubber fuel lines if used a lot, but that’s usually not a problem if parts have been replaced during a rebuild.
I occasionally run a small amount of E85 to clean things out, but I don’t let the car sit with it in the tank. For regular use, stick with name-brand gas and consider using premium if you want extra detergents to keep the engine clean.
@Dexter
If you’re looking to clean out deposits, stick with top-tier gasoline in the correct octane for your car. E85 can damage older fuel systems, even if they’ve been rebuilt. Premium gas doesn’t necessarily have more additives than regular—it depends on the brand.
@Ellis
Actually, premium gas often has more detergents than regular, depending on the brand. Shell’s premium gas, for example, is designed to clean engine deposits. Also, E85 does work as a solvent and can help clean the fuel system, but you’re right that it can damage old rubber parts if left sitting for too long.
@Dexter
Top-tier gas has the same additive levels across all grades. Using E85 as a cleaner can be risky for older cars. Just stick to what’s proven safe for your car.
If you drive it regularly, ethanol gas shouldn’t be a problem. The bigger issue is if it’s been sitting for a while, as that can cause gunk to form in the fuel system.
Try rebuilding the carburetor and replacing the fuel filter. That should solve most fuel-related issues.
Your carburetor and fuel filter are probably full of debris. Ethanol acts as a solvent and can loosen up decades of buildup in the fuel system. Be prepared for this project to take longer than expected—there’s always something else to fix.
You might have plastic sludge in your fuel filters and pump. Ethanol can break down older plastic parts in the fuel system, especially if it’s been sitting for a while.