Looking at getting GLK 250D for my 83 yr old mother. She's an average driver for her age. She's had a GLK loaner a few times while her 2003 C230 Wagon has been dealer serviced. Mom likes the GLK, ingress/egress are easy for an older person. However , I can only find a diesel in the color she likes and her 2003 is not going to be repaired- I will ship it to a friend.
So I can only imagine how long it will take before she fills the GLK250 with gasoline and gets towed in for the big cleanout... Does anyone know if the fuel fill diameters are incompatible in the USA to prevent such a mishap ???
Mom frequents self serve and full serve stations..... I know a story of a full serve attendent filling a 350 Bluetec with gasoline....

In a straight answer, yes. The diesel nozzle has a larger diameter. The gasoline nozzles will fit in the fuel spout with no issues.
Mike T.

Well the Diesel cap on the 250 is RED with big black letters "Diesel"... I hope that this would be enough for her not to put gasoline in it.

It is very easy to make that mistake. Happens with boats all the time with disastrous results. I have heard of one case in NJ where you cannot pump your own gas but you can pump your own diesel. An older gent picked the wrong hose for his diesel. This is especially easy on islands with gas and diesel pumps combined!
I thought Diesel was designated yellow and gasoline Red at least in portable containers. A red cap for diesel? even more confusion.

Actually, mine is green with DIESEL in large letters for 2013 GLK250BT in the USA.

Even so, it can happen since the diesel filler neck is larger than the gasoline nozzle.

BTW, if you ever fill a diesel with gasoline and realize it in time-DON'T start the engine and save yourself lots of cost to clean the entire fuel system.

I am the designated fueler in the family, so hopefully I don't get it mixed up!

Yes.. mine is red. I'm in Canada.

In the US a gas nozzle will fit easily into a diesel - and in most states there is no consistent color codding for the pump nopzzles either - good news is with a GLK250 your # of fill ups will be a lot less..

That's a very good point. I pulled into a Hess station in my area that's known for slightly lower fuel prices yesterday. I noticed the green nozzles and pulled up to the pumps (expecting it to be diesel). But NO, they use green for regular gasoline, yellow for mid-grade and red for premium. As usual, diesel was at a separate pump with black nozzles.

My former BMW 335d is equipped with a Diesel misfueling protection as shown in the picture below.
I wonder why other manufacturers like M-B, Audi and VW doesn't equip all their Diesel vehicles with this.

Clever design. Are you sure this is not in the MB?

Only BMW has it. M-B/VW doesn't.


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Thanks for all the replies. Probably will get her a gasoline GLK. Mom is an elderly driver , only getting older . Reason for my post was we needed a car, it was the end of the month , only cars with Mom's options/colors were diesel, and dealer was offering deep discount on the last day of JUly to meet their monthly number. I understood that and tried to work with him and would have labeled the diesel fuel with yellow paint marker on the cap and the inside of the door to prevent a mishap. However , in the "old lady" spirit of things , Mom wanted to not miss her weekly piano lesson the evening of the 31st rather than save a few grand on a new car. So she will continue driving a GLK350 rental until she picks a car.
MB could make a yellow fuel cap for the Diesel. Or do something like that BMW system. I have a working barn with 4 types of fuel, so I color code everything for my sanity and safety. If you diesel owners don't own a yellow paint marker, buy one (tractor supply, crafts store). Great for labeling your tires, oil filters, etc.

Good plan since your mom is unlikely to drive a lot and mainly local trips a Diesel is not suitable plus the risk of misfueling is high of someone who is not used to driving a Diesel.

Perhaps you could also consider the new B200 series or a C250?

The rush is over since the "deal" isn't as sweet anymore. But that gives us time to find a gas GLK350. I will have her check out the C250 sedan. Ingress/egress out of the GLK is good for her, though there is a big blind spot out the back corners, so rearview cam is a must- hope she uses it. Her 2003 C240 Wagon has better vis out the rear, but needs $4000 and she wants new wheels.....I just want her in something safe and user friendly. I think the diesel fuel fill would just be an accident waiting to happen. I do like the lane change avoidance feature on the new cars- works great in my C63 coupe and it's nasty blind spot.

Hopefully this thread will help someone who owns a GLK250 prevent a nasty repair bill. Aftermarket engineers take note- yellow fuel cap with red letters diesel only and maybe a simple yellow plastic 6x6inch sheet with the filler hole cut out that you push over the neck emblazoned with "diesel only".

hi DC*;
Thanks to this post now I have the info I was looking for! So thanks a lot DC* & the Audi Dealer wont let me copy their service manual pages *d.rats*


We have an Audi q7 TDI which has this mechanism, Previously we have the X5 D and also had VW tdi which didn't have this contraption. my GLK don't have this also!!!


now in emergency cases; we cannot use a GERRY CAN to fill the AUDI Q7 with diesel - so was looking for info to by-pass this FILLING FEATURE ( which I fully support and LIKE !!)


Also to the OP
pity you have already decided to buy non-diesel GLK. I can assure you that using this 'filler mechanism' there is no way to fill a "petrol' into that diesel tank (well provided the gas nozzle are correctly installed at the GAS STATION. Often I have noticed that when they REPAIR THESE PUMPS and they don't have the APPROPIATE CORRECT NOZZLE for that TYPE OF FUEL/GRADE - they mix and use anything the repair-tech has on hand and they fit it and never come back to REDO them CORRECTLY) Diesel nozzles have the smaller 'size' pipes in the end (at least in USA codes that I know off)
My Grandad still loves his GLK (2013) and its his 2nd one in 10yrs! Loves it as he can get in and out without having to 'crough down or sit on his tommy' ((his words)) getting in and out is easy peezy !!


Cheers and happy motoring


Thanks again

What is the difference (honestly) between putting gas in a diesel, and diesel in a gas engine other than the amount of pumps in a station selling both gas, and diesel. Where I live the fuel stations have maybe 5 rows of pumps with only the outermost rows of pumps with diesel fuel dispenser pumps, so I would surmise that the chance of misfiling is about 60% higher putting gas in a diesel if you are stopped at a gas only pump.