jhpmbusa

Do you put regular or premium gas? I am getting mixed review, I believe the E300 is recommended to take premium gas but does not need to.... besides the few bucks and the regular reasons. is it really necessary to use premium on a 4cyl?

knoppe01

I think there will be a temp effect. Last week here in the Northeast it was brutally cold. My car (2017 E300) had no issues I only use premium gas. My wife's car (2016 GLC 300) ran a little rough till very warm and starting was rough too. She "cheats" on the gas.

Lanzz

I'm only using premium in my E300 because I think forced induction engines, especially small displacement ones, work very hard all the time. Especially in hot weather, I think premium fuel is important.

Also, if I read it right, Mercedes says premium fuel is required versus some cars which say premium fuel is recommended. (My Chrysler 300c was premium fuel recommended, so I used it only in hot weather...)

Given that premium fuel is required, I would hate to be in a situation where there is an engine issue and there is a question about warranty coverage because premium fuel wasn't used. So - cheap insurance.

Cao Black

This discussion has appeared in the past...more than once.

Octane is a fuel's ability to resist "knock", which is the explosion of the air/fuel mix by compression rather than by spark. Higher compression gasoline engines generally require higher octane fuels to help prevent this pre-ignition. Lots of engineering went into developing and making your car's engine meet all of the customer and marketplace demands, such as horsepower, torque and 0 to 60 times, not to mention fuel economy; political and environmental regulations such as ethanol in this country; and the variations in fuels throughout the world, such as no European equivalent to 87 Octane Regular (they calculate Octane differently). The engineers concluded that Premium grade fuel was best.

Having said that, you might get away with using 89 Mid Grade, but I would not recommend using 87 Octane Regular. The car wasn't engineered for it, and must use the engine management and anti-knock systems to compensate for the lower octane fuel. Who knows what the long term effect is on your "expensive" car, or even the day-to-day change in performance. I mean, you didn't buy a Kia, you bought a Mercedes. Maybe it's not worth saving a couple of bucks. What do others think?

froll

Driving a $65 - 75,000 car that get great gas mileage deserves premium. Gas prices shouldn't really be a factor

NFAREVIEW

What do I think? I think I'm happy you wrote all that so I didn't have to! Perfect explanation! Thanks! It amazes me how far people get in life without simple knowledge of engines. I grew up learning with my hands, not sitting inside wasting away in front of a TV. I rebuilt my first car engine at 16. I just see the world mechanically I guess and surround myself with like minded individuals. So, as stated before. It's not a KIA. It's a Mercedes Benz. If 40 cents per gallon breaks the bank, you bought the wrong car.

(I don't feel like being politically correct today, don't take my statements personal. I'm saying it how it is)

elnos

When you look at the gas tank cap, you will see minimum octane is 91, and US only has 93 that's above that, so it should be Premium all the time imo.
Fuel you tank with lower gasoline grade will decrease the performance of the car as well as MPG.

The_Judge

One interesting development that affects the need for high octane fuel is direct injection, such as the 3.6 liter V-6 GM has used in its 2008 and later Cadillac CTS. Although that engine has a compression ratio of 11.3 to 1, it runs smoothly on 87 octane fuel.
http://autoweek.com/article/technolo...oweek-explains

petee1997

I'm told you save nothing using 87 octane because your fuel efficiency decreases. In the end, what you saved on the fill up , you gave back on the distance covered. There is no point reinventing the wheel. If the car was designed by some of the best engineers in the world for 91 octane, suck it up and use 91 octane.

makris0000

Just use what is recommended. Don't be cheap.

cetialpha5

The btu content of regular and super/premium is the same. Fuel efficiency will only decrease if the engine detects knocking and retards the timing. If the timing isn't retarded, the gas mileage should be the same. As others mentioned, the octane rating is only the ability of the gasoline to avoid pre-detonation has nothing to do with the energy content of the fuel. E10 and E85 will give you worse gas mileage because ethanol has a lower btu content than gasoline.

Cao Black

Good points...but how do you know that your timing isn't being retarded? The engine doesn't have to be "dieseling" for the sensors to react. Plus we really haven't addressed the issue of turbo chargers (or superchargers) forcing more air into the cylinders, which increases pressure and contributes to the need to have fuel which won't pre-detonate. Best to use what the manufacturer recommends.

petee1997

That may explain the better mileage. Shell 91 octane in Canada has no alcohol where as the 89 and 87 can have as much as 10%. Shell is the fuel I use.

cetialpha5

A gallon of gasoline is about 114,000 btu's whereas a gallon of ethanol is 76,100. So a gallon of E10 is about 110,000 btu's per gallon. It's why E85 normally doesn't make sense unless you're in the corn belt, the cost per btu price is higher even though the cost per gallon may be lower than gas.

Cerave

Anyone using 87? I want to know if it’s actually bad for the engine or not.

Does it void warranty to use 87 or 89?

whoover

This is what the manual says. They could be taking bribes from Big Oil. Or they could know something about operating their engines.

DFWdude

I don't know how this applies to Forced Induction engines, or for engines with Direct Fuel Injection.

But...

Once my 2001 3.2L V6 C320 exceeded its 4-year warranty, I've used MIDGRADE (89 oct) in the 14 years since. No pre-detonation knocking, no rough idle or other ill effects.

The car did NOT like 87 octane unleaded Regular, which apparently fell outside the adjustability range of the onboard computer. (I tried this only once on 1/2 tank... When it started complaining I immediately topped-up with 93 Octane Premium).

So I can't recommend 87 octane Unleaded Regular.

cetialpha5

Never really tried midgrade. It's basically just a mix of 1/3 super with 2/3 regular to get 89 as we have 93 here for super. If you just have 91 for super then it's just half and half. But it's priced about 10-20 cents a gallon higher than if you just made your own mix and filled up twice with two different grades.

rewillia

Premium cars call for premium fuel. I personally purchase the highest octane at the pump for any of my vehicles. Always have, always will.

Cerave

Good to know, thanks

JTK44

Been using regular gas in the following cars without incident: all had electronic knock control:

1. 1999 BMW 740i
2. 2001 BMW 740il
3. 2005 Acura MDX
4. 2008 Acura MDX
5. 2011 BMW 535i
6. 2013 BMW 540
7. 2016 Mercedes E350
8. 2019 Mercedes E450

By using regular vs. premium you lose between 5% and 7% of the peak horsepower. However, unless you are drag racing, pulling a trailer in the mountains you will never notice the difference. Remember at 70 mph you are only using about 18% of your horsepower.

I have also checked MPG regular vs. premium and I have found NO difference. The only difference is in your pocket book.

baadmon

Premium for me, no question about it!

The_Judge

Ditto. I'm cheap, but not THAT cheap!