Welcome to the GLA forum Wingsy. Where are you located and what are the actual premium and regular octane ratings? Was the tank level close to empty when you changed to regular? From your mileage numbers you appear to have some mixed driving conditions. Have you noticed any difference in performance or mileage on the open road? Just curious.

 

Mileage generally takes several tanks to discern.

FWIW Pam and I got about 2 mpg more in Europe with 93 compared to the 91 here in California (28 vs 26). Europe was 2500 miles on a new motor. California mpg was based on an equal number of miles.

But conditions weren't exactly the same.

Then, with just under 6000 miles and new oil, we ran just under 30 mpg over 1000 miles last weekend. Still 91 octane. A combination of heavy LA traffic and then 80 mph up the 5.

In other words, my data doesn't prove much. But mpg is like cholesterol readings ... very noisy. Your data probably doesn't prove much either.

I don't believe regular is ideal. The 2017 GLA45 specifies 91 or better. I believe the same is true for the 250.

Higher octane gas burns slower stretching out the power stroke and putting less strain on the motor. I would be hesitant to run regular.

 

Are you experiencing any ping or knock from your engine with regular unleaded? Like Wayne, I'm hesitant to try it. We were told we could use unleaded if premium was not available, but we should top off with premium as soon as possible afterwards. We don't drive ours hard, so I'm not worried about performance, but I'd hate to experience engine damage as a result, any cost saving from using regular would be severely negated at that point!

 

I will just say this, I had a longtime Benz mechanic (he had done a lot of the restoration on our W123) tell me that the M104 in my my C class could run on regular "all day". It did, until I had to make a 4 hour road trip out to my college. Went into limp-home 3.5 hours in, nearly stranding me out in the high plains. Never put regular in again, never had it go berserk again. I swung the other way with that car, putting in exclusively Shell and Chevron after that. I don't have the same availability here, but when I fill up on the road I only go to Shell stations.

My belief is this - the ECU will record what octane goes through it, as it can "sense" it through burn rate, intake/exh temps and the like. This gives the dealer fodder to deny any warranty claims. Also, when I went to pick up mine *at the factory* I already knew more (from lurking here) than the rep who did the handoff. I believe sales rats about as far as I can throw their dealership with one broken arm on a monday morning. Put regular in at your own risk, imho.

 

Good points Third Phase. I have come to believe in Techron and use Chevron almost exclusively. But now and then I switch to Shell for a fill up just to get a different cleaner. It may cost a bit more, but I can't measure the value of piece of mind.

 

To the OP: IF your dealer told you you could run regular gas on this 2L Turbocharged 4cyl... I recommend you run from that dealer as fast as you can.

 

I would never run regular fuel in a Mercedes engine. It's not just the octane level that makes a difference, the fuel is a more pure fuel and has more cleaners in it. The same reason you should never run regular fuel in a small engine (lawnmower, snowblower, boat etc). The premium fuel has less stuff in it that will clog or otherwise foul up your engine. You bought a premium luxury vehicle... Was saving a few buck on you priority list? Probably not. No one likes to give the gas companies any more money than they have to, but in my opinion, this is something you should not cheap out on. Just my 2 cents.

 

I whine about the price difference between 93 and 87, then I go to fill up with 93, and it only costs $18.95. The mileage is so much better with the GLA that I don't mind using 93, and yes Wayne-the manual, at least in 2015, says to use minimum 91 on the GLA250.

 

It isn't about MPG - its about how much energy from each gallon the engine can get. When lower octane fuel goes through a high compression, high stress engine, the ECU retards timing to allow for the lower octane fuel.

Lower octane does NOT equal lower quality - it simply means that at a given compression, that fuel will explode sooner than higher octane fuel. Fuel will explode under pressure - in fact, that is how Diesel engines work - they have no spark plugs, they just compress and explode over and over.

So - by buying cheaper/lower octane gas, all you are doing is having your ECU take performance away from you. Period. You will probably get the same amount of MPG as you did with higher octane in normal driving conditions, but it sure won't be at the same performance. That's it.

As for "can" use lower octane fuel - this is even in the manual... you can. It suggests not to as performance will suffer and only to do so in case of emergency.

 

I guess I'm the odd ball on this subject because Since I first purchased a Benz in 2001 I have used nothing but REGULAR unleaded. I have yet to hear engine noise,valves singing or anything else like that. On the other hand I had a 2014 BMW 3 series and that one DOES sound bad when using unleaded..valves singing. In summary use what makes you happy, I'll continue using regular and if I have engine failure it will be the first and I'm not too concerned.

 

Small high compression engine like the one in GLA doesn't fair well with regular gas. A ping could easily destroy the engine although most times, the ECU can adjust to adapt at the cost of power output. In fact, my 2017 GLA 250 clearly labeled on the fuel door 'minimum octane rating 91'.

Don't confuse it with bigger, otherwise no so highly compressed, engine you used in the past. Not the same thing. I will never use regular fuel on any turbo charged engine unless it is designed for regular gas.

 

I traded a Beamer 328i for this GLA, and I always used regular in it, without issue, because the dealer said I could when I bought it. I never had any noticeable issues over 4 years. This is about Benz number 12 for me, back to 1967, and it is the first one I have used premium with (not including the diesels). I decided to do this because the manual does not give you a choice for permanent use, and members of this forum have made a persuasive case for the value of higher octane in the turbo four engine. The mileage is so good that even with the higher price, the cost per mile is low, possibly lower than the cost was for the BMW.