Sudden mpg drop

[Coolbreezin]

Hello all. I have a 2017 Premier which I bought new. I normally got about 34.5 mpg. At about 55,000 miles my mpg suddenly dropped by about 2 mpg and I cant seem to get past it. Figured my air filter was dirty, it was not at all. Cleaned it anyway. I did buy new tires, but this happened a little before that purchase. Ive used 89 octane since day one. Now I use 92 and it makes no difference in my mpg. Now call me a cynic, but I am entertaining the idea that perhaps certain things are to happen at a particular mileage.
Any advice?

 

[Coolbreezin]

Bueller, Bueller...

 

[Chuzz']

I don't really know much about these cars as I don't own one, but I'd do a spark plug change on it and see what happens. Some cars nowadays come with 100,000 mile plugs in them, but IDK if the Sonic is one of them. Check your owners manual for plug change intervals and follow it. And just stick with the OEM style plug. All the hype about high mileage plugs, four tip platinum, split electrode, lithium etc. etc. are sales gimmicks. Chevy put the OEM plugs in there for a reason. Carry on.

 

[Coolbreezin]

Good info. Thank you. Ill do it this weekend.

 

[Chuzz']

I'd also recommend you get a bottle of TECHRON Fuel System Cleaner and put it in your gas tank before your next fill up. I've been running that stuff in my cars about every 10,000 miles for over 15 years now and have NEVER had a fuel injector issue. That is the only brand I'll use, but to each his own. I alternate the Fuel System Cleaner with Fuel Injector Cleaner every 10,000 miles. Forgot to mention that. Sorry about that.

 

[TboneMinister]

I don't really know much about these cars as I don't own one, but I'd do a spark plug change on it and see what happens. Some cars nowadays come with 100,000 mile plugs in them, but IDK if the Sonic is one of them. Check your owners manual for plug change intervals and follow it. And just stick with the OEM style plug. All the hype about high mileage plugs, four tip platinum, split electrode, lithium etc. etc. are sales gimmicks. Chevy put the OEM plugs in there for a reason. Carry on.

While I'll conceded that OEM plugs are probably the best option for a stock vehicle, I wouldn't call other plug options "gimmicks" on non-stock turbo'd cars. Chevy put the OEM plugs in there b/c they were the cheapest option that functioned well within the stock performance parameters.

 

[Chuzz']

Key words being "functioned well". No disrespect intended and thank you for your service. One of my favorite uncles was in the Marine Corps in WWII.

 

[gnonne]

Maybe plugs, but doubtful at this mileage.

How do you know the the mpg dropped? Maybe it is the new tires (very common as the stock tires are light to get higher mpg) and it took the computer a couple of tankfuls to show the lower mpg? But, if you are finding mpg "by hand" that isn't the problem.

Also, I don;t know about 89 or 93 gas. They are set up to run on 87. I've had three Sonics and never noticed any advantage to using higher octane gas. I know people will yell at me for saying this, but if you use good oil, change it regularly, and run injector cleaner through it when you do the oil changes, you will not have engine issues.

 

[Coolbreezin]

Maybe plugs, but doubtful at this mileage.

How do you know the the mpg dropped? Maybe it is the new tires (very common as the stock tires are light to get higher mpg) and it took the computer a couple of tankfuls to show the lower mpg? But, if you are finding mpg "by hand" that isn't the problem.

Also, I don;t know about 89 or 93 gas. They are set up to run on 87. I've had three Sonics and never noticed any advantage to using higher octane gas. I know people will yell at me for saying this, but if you use good oil, change it regularly, and run injector cleaner through it when you do the oil changes, you will not have engine issues.

The mpg drop happened before the new tires.

 

[Coolbreezin]

After 3 tanks and cheapo Walmart injection cleaner, my mileage is back to 34 on 92 octane. Im happy. Im going to test the octane theory after this current tankful. Thank you all for yr input and guidance.

 

[TboneMinister]

After 3 tanks and cheapo Walmart injection cleaner, my mileage is back to 34 on 92 octane. Im happy. Im going to test the octane theory after this current tankful. Thank you all for yr input and guidance.

The Sonic has a fuel map for both low and high octane fuel. While you can technically run regular fuel, I would never suggest doing so with any forced induction engine. If you have the GM Performance Exhaust/Turbo Stage, Premium is required. If you are running a tune, you really need to run Premium. Even if there are no immediately noticeable benefits stock (MPG, HP, Tq), I can't imagine it not making a significant difference in the long-term health and reliability of the engine.