Miles Per Gallon Issue

[Revolverreaper]

I have a 2016 Chevy Spark that can hold up to 9 gallons of gas. I bought the car in 2016 and typically after I fuel up the display next to my speedometer will say between 335 and 355 (37-39 miles per gallon).

I got my oil changed, got four new tires and they did an induction cleaning and a coolant flush.

The next time I got gas, the display read 305 despite the fact that the tank should have been full. I had to drive a long distance and later that day I got gas again and the display then read 268. This has happened several times now.

The weather change has not been extreme. I am now getting significantly less miles per gallon on the highway than before my visit to get my oil changed etc. I am asking for advice on what could have happened to create this issue.

 

[wi5pa]

A) The sensor in the tank could be sticking,

B) Clearing all the carbon from the induction is allowing more fuel to enter your combustion chamber, hence more fuel comsumption,
but you should also notice a better performance too.

There could be more but these came to mind....

 

[USAFRet]

You're checking gas mileage incorrectly.

You need to record over time.
Start with a 100% full tank.
Note the mileage on the car.
Later, refill. Note how many gallons, and the current mileage.
Repeat over a few weeks/months.
Divide out, that is your overall gas mileage.

 

[Revolverreaper]

Thank you for the response.

The weekend before getting my oil changed, I took a 345 mile trip on one tank of gas. Over the four years that I have had the car, I have consistently gotten around 39 miles per gallon. The only change has been getting my car serviced at a new location.

I had no issues previously and on the trip after getting my oil changed at the new location I am getting 29 miles per gallon. That is a big enough difference to cause me to worry.

Also, my fuel gauge is digital.

 

[USAFRet]

There is nothing in the context of an oil change that could reduce gas mileage by that amount.
Unless they neglected to put in any oil at all, and it is running dry.

 

[hang-the-9]

Thank you for the response.

The weekend before getting my oil changed, I took a 345 mile trip on one tank of gas. Over the four years that I have had the car, I have consistently gotten around 39 miles per gallon. The only change has been getting my car serviced at a new location.

I had no issues previously and on the trip after getting my oil changed at the new location I am getting 29 miles per gallon. That is a big enough difference to cause me to worry.

Also, my fuel gauge is digital.

Battery wears out over time which means the gas engine would be pulling more, temperature affects battery also for range and how well it will work. Test things over a few weeks of travel with full fuel tanks, measuring the miles and gallons needed for a fill-up and see how things go.

 

[kanewolf]

You got new tires. They may have a different rolling resistance than the originals. You should also manually check your tire pressure with a high quality dial type tire gauge.
Cars sold for efficiency have low rolling resistance tires. Did you put the same tires on as were on previously?

 

[ttower2020]

I assume you got winter tires put on, going into winter. They will decrease your MPG, and the new tires might not have the correct PSI. Normally this is not a huge issue, but with the Spark being a lower powered car, that small difference would be exaggerated.

 

[gggplaya]

Did they do a proper cooling flush using an expensive machine to pressurize and "flush the system."

Or did they do a coolant change and run the engine with a hose in the radiator, using the car's own water pump to "flush" the system?

If they ran the engine for a while for a coolant change, that would explain why your computer thinks you get worse fuel economy than you actually do.

You need to use Fuelly, an app on your phone, to record your mileage and your fillups. It will calculate your real fuel mileage.

 

[punkncat]

I would also mention that new cars are particularly picky about the weight of the oil used. If it spec (for instance) 5-30 and they put in 10-40 it would make a difference like this as well.

By and large you may have something else going on. If they used a chemical spray on the intake area it could have messed with mass air, or any number of other factors. Some great points made above as well.

 

[gggplaya]

I would also mention that new cars are particularly picky about the weight of the oil used. If it spec (for instance) 5-30 and they put in 10-40 it would make a difference like this as well.

By and large you may have something else going on. If they used a chemical spray on the intake area it could have messed with mass air, or any number of other factors. Some great points made above as well.

Most fuel mileage sippers use 0w20 or 5w20 oil. Shop might have put in 5w30 because 0w20 is always full synthetic. They might have ripped you off and put in conventional oil, 5w30 most likely. Or they only buy 5-30 or 10-40 by the barrel load and only put that into customer cars.

Is it a reputable shop you went to, or one of those quick change places?

 

[Deleted member 14196]

Yeah I only use reputable shops and I really only use full synthetic anyway. I like the Amsoil Signature stuff. Make sure you are using a good shop they can be trusted and take note of all the things that are mentioned above especially about flushing the cooling system