Hi Folks.

Recently purchased a 2016 GL350 early February. Have 4000 miles on the odometer now, and it seems that the mpg is going down, instead of up, as the car is breaking in.

When I first got the car, the car averaged 20mpg. After couple tanks, the average mpg of the trip computer started to drop to about 19.6. That means that it's actually getting worse than that and pulling the average since day one down.

I thought it was because I lowered the tires to 38psi. So I raised them back up to 41 front and 43 rear and reset the trip computer. Well... few tanks later, I am averaging 18.5mpg. That's with about 30% highway and 70% local.

I don't drive like a teenager and since I usually drive my 2 preschoolers around, I'd say I drive more like a grandma, no hard accelerations, no hard braking, no long idles. It's getting almost the same mpg as my 08 ML350, which has 180k miles!!!!!

Oh, I tried diesel kleen cetane boost for couple tanks to see if it'll help, NADA!

I understand that the engine is still a little green, but this doesn't feel right...

Any thoughts?

What type of trips? Diesel emission scenarios don't return stellar short distance, low operating temp MPG's. Longer, the better with a diesel.

Also, might want to calculate MPG's via mileage traveled and fuel used. EVIC calculations, especially early on, can be all over the place for various reasons.

Morning about 12 miles round trip droping off kids at the school, then 50 mile round trip twice a day.

I am not sure about what EVIC stands for, but judging from miles traveled per tank when filling up, the mpg from the trip computer is pretty close.

I live on a hill, I'd say 1500 ft, and it's about 3 miles to the freeway. I just came to work, and reset my trip computer when I left the house. After coasting the way down, feathering the throttle to the freeway, and keeping it at 70~75mph, I got 23.5mpg. Is it me or is that still a little low?

Short trips will kill your mileage.

I come from a diesel X5 (traded for a a GL550 a few weeks ago), which usually got great mileage, and in normal conditions should do around 18-19 city, but since my office and kids school are less than a mile away, I used to get about 13-14 mpg.
On my GL550, same daily trip hovers around 7 mpg, and 9.9 mpg overall average per tank. When I take 5 or 8 mile trips, I get to the 12-13 mpg official numbers around town. As they say, your mileage may vary...

Neurobit

Mine is 2015 GL350. 20K miles average per computer is 19.1 mpg. I go to Florida once a year and get about 25-27mpg depending on my speed. Usually it's 75-80mph. Driving in the city, I mean NYC area, I've never seen more than 13-14mpg. It gets better as soon as I get to any highway.

We consistently get 21 mpg over a tank full of diesel in city/suburban driving which is comprised mostly of short trips, and 25-26 mpg over a tank full when driving 80 mph on the highway. I have been very impressed. 2015 GL350, 11k miles on the odometer.

That's what's confusing me. Seems like the numbers are all over the place. All the specs and the test drives reports 22mpg over mixed driving. Like aeggroup reported, getting 13-14 mpg in the city, 19.1 over 20k and Lone Stare Benz reporting 21mpg over mixed short trips. That's too wide a gap.

My 08 ML350 is rated at 15/20. And I average 18.5, that's driving under the same pattern that I am driving my GL350 now, with a lot heavier foot and spending a bit of time idling if the kids falls asleep in the car after arriving where we're going.

Since the point of getting the GL350 over the GL450 is giving up 2sec 0-60 performance for the mpg. I've been driving it like an old lady. No heavy footing at all! I would understand if I am not getting the 22mpg reported mix driving, since I live up on the hill. But at 100+ miles a day, I spend plenty of time driving on the freeway, getting below the city mpg rating is just not right!

Can someone explain why such a wide gap? Also, as I reported earlier, I took a trip, coasting down hill, feathering the throttle on the freeway, maintaining 70-75mph, and still over averaged 23.5mpg over 25 miles, that's still way below the rated 26mpg that I'm sure is down with a heavier foot and without the 3 mile down hill coasting.

Just a little confused and frustrated...

I understand your frustration, but there are so many variables. Your definition of short trip may be different than mine or someone else's.
Also, traffic plays a huge part also. Here in Houston, it has become a nightmare in the last two-three years, so even longer trips around town, or on freeway drives, our vehicles return mediocre MPG, where perhaps someone living in a less densely populated area will do much better even on short trips.

Neurobit

I agree with Neurobit about the variables. If you typically drive a 30 mile round trip, your mileage might vary 2-3 mpg for the trip just based on how many traffic lights you hit. On the freeway, the direction and speed of the wind can have a huge effect on your mileage. You can drive west into the wind on the freeway and get 21 mpg and then drive east and get 30 doing the same speed. The air temp can also have an impact as the transmission will hold a higher gear longer if it needs more time to warm up the engine/catalysts etc.

One of the nice things about switching to the 550 is I stopped worrying about that stuff.

I understand these variables. My 08 ML350 which is rated at 15/20 with 180k miles is doing pretty much the same under the same conditions, same traffic, same distance.

Problem is, I drive the ML350 with a much heavier foot, wasn't trying to get the best mpg out of it. If I feather the throttle the same as in the GL350, the 180k mile ML350 will actually get better mpg than the new diesel GL350!

Ditto...

I did not switch to 550, and I don't worry about this stuff as well.

My 2015 GL350 has 30k miles in 17 months. Granted, most of my miles are highway. Averaging 25 mpg highway and when I'm driving around town for a few weeks I'm getting just under 22 mpg. Maybe a trip to the dealer is in order.

Thanks for the input. This is the kind of input I am looking for. Your numbers are pretty much same as the rating for these cars. The reason I am asking is if anyone knows about issues that'll effect mpg that I need to be concerned about. Like there was a post regarding adblue pump wasn't addressed til a CEL showed up.

It's not so much the extra money paid for the diesel. After all, with the money paid for these suvs, it doesn't make that much of a difference. I just can't stand driving around when my car is not performing 100%.

Car's at almost 5k now. Guess I'll wait til the 10k service to bring this up so they won't give me the break-in mpg nonsense.

Quite frankly, any competent dealer should take your issue seriously NOW. I'd give it a go!

Something odd just happened. With same traffic, driving style, distance, heck, even same gas station and same pump, my last tank just shot up to 21.3 mpg..... the od turned 5500 just before this past tank......

No long trips, no other driver, just same old boring day to day stuff......

could it be some sort of break-in setting in the ecu that turned off at 5500 miles? I can't understand what changed. 18.6 > 21.3.......

I know you have a TD but when I got my GL550 the local driving mileage was well below average. I'm used to vehicles with terrible gas mileage but this thing was extremely trirsty to a point I thought something was wong. But when I hit around 5,000 miles, it suddenly shifted and the mileage is very much inline with published figures and has been getting better since. I suspected an ECU break-in trigger myself and you might be onto something. Even the engine performance the first few thousand miles felt a little underwhelming, but around 2,000 miles it turned into a complete beast/rocket ship. It's stupid how fast this truck is.

Keep in mind all TDI's go through a regen cycle occasionally. I don't know the conditions that start that in a GL, but it could very well be to blame for a period of lower gas mileage.

So when's the tune and DPF delete come out for GL's?

We've also noticed over the two years with the VW TDI, it gets better mileage in warmer months vs winter. The car is parked outside, so not exactly sure what the cause/effect specifically is, but it is noticeable.

Talked to tech once about it and he said something to the extent fuel temp, emissions sensor temps , etc ....


Then VW scandal hit and I just crossed all that off the list ...

Depending on your location, winter ULSD is cut with up to 40% kerosene to prevent fuel gelling. My experience in over 15 yrs owning and operating diesels, winter mpg's take a significant hit and so does performance. Sounds pretty normal to me as the fuel is transitioning from wintererized fuel to straight #2 ULSD.

The GL uses CDI and is not a TDI system.

If your mpg started suffering recently, you might want to check your brakes. Mine rear inner pads was slightly sticking and MPG got reduced from 25 to 21.

25mpg? Is that hwy or combined?

Mine's been averaging around 21 since 5500 miles.... while I thought that's acceptable, I've been driving like a grandma..... I used to think driving like a grandma would yield above window sticker rating, but I'm barely achieving 21... not to mention 22 combined...

If I drive normally, meaning occasional harder acceleration, and 85~90mph, it's more like 18.5~19.1 ...

Life's been a little too busy for me to schedule a trip to the dealer, I'm at 7500 miles.

any diesel driven like a grandma would make it probably get lower mpg. Especially short frequent trips. Its probably going into regeneration and that will make mpg go down. You got to drive the diesel aggressive to help burn off the deposits on the filter

My idea of grandma is slow acceleration and coasting as much as I can, trying to keep rpm down and trying not to acceleration too hard off lights and freeway onramps. I still drive 10 over speed limit, 75 or so on freeways, and 75~100miles a day. That's why I'm at 7500 miles since getting the car at Feb.