I have 2013 4cyl GMC Terrain which is less than one year old, 18445 miles. The EPA sticker says 22-32 MPG…I realize that I won’t get that mileage, BUT 14MPG city is a tad ridiculous! Car had issue with engine light coming on and got it in to service and was told “a hose was loose”, they fixed that, no more engine light, but since gas mileage has gone down. 18 MPG, 16 MPG, 16 MPG, 14 MPG city on last 4 fill-ups! contacted GMC, started case, contacted my local dealer and all they said they would do is a mileage test on highway! What could be causing this problem and am I getting proper help from GMC/local dealership?
Nobody from afar can know the exact “city” conditions under which this car is driven, nor can they know your driving style. It is possible that, under the conditions in which this vehicle is driven, 14 mpg is “normal”.
However, I will give you a few suggestions that could help, at least a bit:
Check the air pressure in the tires. At the very least, the tires should be inflated to the pressure listed on the label affixed to the driver’s door jamb. Two or three lbs additional pressure may help increase your mileage.
Make sure that you are not “warming up” the engine. Modern vehicles can–and should–be driven within seconds of starting the engine.
Do not use drive-up windows at banks & fast food joints. Instead, park the vehicle, and walk inside.
Learn to anticipate traffic lights as much as possible. Rather than racing from one red light to another, try to coast up to traffic lights, and then accelerate gently away from them.
Take any excess weight (tools, extra tires, sand bags, etc) out of the cargo area
Something like a bad coolant temperature sensor could cause the engine to run rich and burn more gas than necessary, lowering your mpg. A stuck open thermostat can have a similar effect.
Good comments above. Esp, if you vehicle has a coolant temp gauge, make sure it is reading the same now as when the mpg was ok. Low coolant temps are bad for mpg. Also, maybe ask the dealer to put their exhaust sniffer on the tailpipe, see if the HC’s are high, indicating unburned gasoline is coming out the exhaust. If so, anything the shop manual says could cause a rich mixture is worth considering, and checking the valve clearances might be worthwhile.