Really bad fuel economy

[yeahforbes]

Stock 2017 Golf R. Fuel economy spec is 23 city / 30 hwy / 25 combo. Over MANY tanks of gas (say, the last several months) it has dropped to 12 city / 23 hwy / 20 extended average. And when I check hwy, I'm not going crazy speeds... I just drove 45min at about 40-65mph, cruise control mostly, and got 22.8 mpg.

I'm at the dealer (prepaid, so why not) for my 30K service for the next couple hours. Just had a conversation with the service director about it... first thought was winter gas (but this has been going on too long for that), second thought was unfortunately I don't quite reach 200F oil temp on my 2.5mi city commute (but I typically get on the highway at least once a week) so it could need a fuel injector cleaning, but instead of pushing the sale they suggest waiting for summer gas first. Thoughts?

 

[mopar22]

Throw some fuel injector/ fuel cleaner in your tank. Get up to an temp and on a decent highway cruise with average fuel economy reset. You could be looking at long term fuel economy and if that's the case with your short trip it will be super low

 

[Diggs24]

2.5mi city commute

 

[olds350]

if it's not coming up to temp, there may be a bad temp sensor and it's keeping the car running in a "rich" fuel state, so that would account for poor fuel mileage. Once it reaches normal op temps, it should lean out the fuel.

 

[reallypeacedoff]

I live in LA and it takes at least 2.5 miles just for the temp to show (122) so I cannot imagine you even get close to there in NJ. I don't drive my car as much as I used to so I only drive on weekends and usually go through a full tank driving it very hard and I get better mileage than you. Stage I too. I mean, my worst tank was following a bunch of supercars around Malibu and I got ~12mpg and pretty much had my foot to the floor the whole time. I'm also at 50k+ miles. Unfortunately, you need to run the injector cleaner about 1,000 miles before an oil change. I did it about 4k ago and it felt a lot livelier. I drive fairly differently each time I drive the car so not sure if I could quantitate an MPG increase.

 

[sterkrazzy]

45 minutes at 40-65 mph definitely should have gotten you closer to 30mpg. Your 2.5 mile commute to work will never have high mpg, you need more driving than that to get the average up.

 

[GTIgolfmark7]

Had the same when doing short drives, new job is twice the distance and getting much better mpg
Short trips w cold engine r really bad for fuel economy

 

[JC_451]

It's the short trips.

I also have a very short commute. In the cold months the oil temp never even gets past --- unless it's snowy and I drive in 2nd gear the whole way. Are you talking about the coolant temp? If you're not even hitting 196 on the coolant you're probably getting single digits for fuel economy on the way to work.

As bad as it sounds that seems totally normal to me based on your usage of the car.

 

[vj123]

I have 4 mile drive to work and during peak winter, i reach office before the engine temp stabilizes. This is a big influence for FE as mentioned several times above.

 

[yeahforbes]

There's a little bit of confusion... I'm not worried about mpg during my commute. Of course that will be horrible. I'm saying that perhaps my short commute = carbon buildup = low highway mpg. Also not talking about coolant temp (that gets to operating temp extremely quickly compared to my Mk5 GTI, actually) just saying how my commute isn't long enough for oil temp to hit 200F, more like 160F then shut off, twice a day. Anyway, my goal is to improve highway mpg, not my commute's mpg.

Good call on injector cleaner and I guess that will have to wait since I just did an oil change.

I am aware of the various averages on the MFD.

GOOD NEWS! Seems like the oil change solved the problem. Previous owner did the 20K service about 8500 miles ago, so call this a "compromise" oil change interval between the 5K some people do and the 10K the book recommends. I always did 7500mi on my Mk5, and only stretched this out to 8500 because of how the prepaid service includes other things I saw no reason to expedite. NIGHT AND DAY FUEL ECONOMY. 23mpg there, 30mpg back. Granted the dealership is 380ft higher elevation so better economy on the return is expected, but I also reset the MFD on a very flat part (I watched the altimeter to confirm) and it was right around 29-30. I was always of the opinion that maybe modern oil is damn good compared to the old days and the 10K interval is fine, but I shorten up the interval anyway. Now I'm convinced that 10K is BS and only to appease customers who value less maintenance. I'll aim for about 7000 from now on, which is when the mpg's started to nosedive.

 

[NCM]

@OP: Also, you haven’t mentioned tire pressures. Cold weather drops them about 1 psi per degree F, and low pressure equals more rolling resistance. Dealer would have reset them to spec during your oil service.

 

[yeahforbes]

@NCM I last topped them up 1.5 months ago (10/25/19). I happen to know the date because it's when they were remounted after being powdercoated! Historical weather data on wunderground says that it was 65F then, and today it was 37F. Haven't bothered to check lately since the winters are about to go on. According to https://tirepressure.com/tire-pressure-temperature-calculator the falling temp brought them down by about 3psi (36psi instead of 39psi spec).

 

[jimlloyd40]

if it's not coming up to temp, there may be a bad temp sensor and it's keeping the car running in a "rich" fuel state, so that would account for poor fuel mileage. Once it reaches normal op temps, it should lean out the fuel.

He's in New Jersey so it's cold and it takes a lot more then 2 1/2 miles for the oil to come up to operating temperature. I'm in Phoenix and at 50 degrees it takes about 10 miles to come up to 220 degrees.

 

[david9962000]

Check your air filter too.

 

[NCM]

Check your air filter too.

Although I checked mine at 20K miles and it was surprisingly clean. Put my new one back in its box for the next time, and returned the original to the car.

Neil