2013 Glk 276 . Has anyone run regular gas? I am trying it. I tried a test , accelerating down an alley with buildings close by, with windows open. I heard no engine knocking. I only get reduced power. But it saves .75c a gallon.

 

This could turn out as bad as an oil thread....

 

Yep. I don’t have anything better to do, so here goes.

They’ll certainly run on regular. I think the owner’s manual says it’s okay in an emergency and fill up with 91+ at the first opportunity. If you don’t drive hard or very fast maybe it’s okay, maybe not.

What long term damage occurs is a lengthy experiment.

(100,000 miles)/(25 mpg)=4000 miles
(4000 miles)($0.75/gal)=$3000
($3000)/(10 yrs)=$300 per year

Some people say use premium because of a better additive package. I checked with Exxon engineers quite a while back and, “Nope.” The additive package, except for anti-knock compounds, is the same across all grades.

 

I haven't experimented on my GLK yet, but have done so on a couple of my cars that called for premium fuel (a 2004 Acura MDX and my 2006 BMW 530xi Touring). I did NOT run regular in any of my turbocharged cars, as I think that's just asking for trouble (since the conditions in the cylinders vary MUCH more than a normally aspirated engine).

I do a lot of long road trips, and doubted that the premium fuel was buying me anything at all on those (with the possible exception of portions that had a lot of steep climbs). I checked the ignition advance on a flat, windless section of road at a set speed, then filled up with regular, and a few miles later (giving the premium fuel in the system time to be used) checked again. In both cases (Acura and BMW) the ignition advance "just driving along" was the same.

In any case, modern engines have a host of sensors that will allow the engine to adapt to the fuel you're using. There's no doubt that you WILL have less horsepower available at full throttle / high RPMs, but I drive like an old lady 99.9% of the time, so this just isn't an issue (and it's certainly not worth paying an extra 20% for fuel).

My plan is to start running regular in the GLK (I've run a tank of premium mostly through it, "just to get used to it", to make sure I'd notice any difference after I change).

 

OK, here's my take.

If it doesn't knock then it won't cause any damage. It is my opinion that this also applies to engines with turbos. Your opinion may differ. The only difference between 87 and 91 is the resistance to pre-ignition/detonation, so if it doesn't do that then no difference as far as the mechanics of the engine is concerned. (If it does knock, change what you're doing right quick. Knocking in today's engines can cause a lot of damage in a short amount of time.)

People will tell you that there are better additive packages in premium. It's not true (already mentioned.)

People will tell you premium is more highly filtered than regular. It's not true.

People will tell you there is more energy in a gallon of premium. It is not true. However, running premium allows the engine to run with more timing advance and/or boost, so the engine can be more efficient, so you might get a small increase in mpg. On the other hand, regular burns faster, so you get more cylinder pressure sooner in the power stroke, so you might get a small increase in mpg. Worth experimenting with.

Of course, if you want maximum performance, premium will make a difference.

Someone might say "it's only $300 a year", but if that $300 gets you nothing, then you're better off running regular and donating the $300 to your favorite charity.

TMSAISTI!

 

I pretty much agree with everything in that post! My hesitation to run regular in a turbo engine is this... I figure under normal circumstances in a normally aspirated engine, the engine management computer will be able to adjust the timing with only a few pings necessary.

On a turbo motor, my assumption is that the faster and larger change in engine compression and dynamics might allow more pings to take place, more often. And once you accumulate enough pings, you might start breaking things.

I may be entirely wrong, but hey, it's a turbo! It's supposed to be expensive! ;-)

 

Here’s a little wisdom from our aviation friends.

https://resources.savvyaviation.com/...-pre-ignition/

Aviation gasoline comes in 80 and 100 octane.

A failure for them doesn’t mean pulling over to the curb, it means a quick trip back to earth from 3000+ feet.

What I noticed is that they consider a high performance engine to have 0.625 HP/cu inch. Our normally aspirated direct injection automotive engines are already running at 1.4 HP/cu inch and the later turbo d-i engines are over 1.8 HP/cu inch.

 

Back when I was younger I had a SAAB 99 Turbo. It was all tricked out and running about 15 psi boost (stock was 7-8, IIRC). No intercooler, but it had water injection. (We used methanol...) Every once in a while the wastegate would stick closed and the boost would go through the roof. The engine made a sound like a 12 gauge shotgun loaded with 00 buckshot had just peppered the inside of the engine compartment! Then, the over boost switch killed the fuel pump, giving you whiplash...

Knock sensors didn't come along until a few years later.

Never blew up, though!

 

Those old air-cooled aircraft engines were real dinosaurs. Because they were direct drive to the prop, they could only turn about 2500 or 3000 RPM at red line, which was for the prop, not the engine (to keep the tips from going supersonic). They had no sophisticated electronics at all, and having fuel that didn't have the proper octane could result in melting pistons or valves. I once pre-flighted the Cherokee I was flying, and saw that the hanger guys had filled it up with the wrong fuel, which is color coded. Made for a long day with little or no flying as I recall. :-)

 

Air cooled made a difference along with the fall from the sky.

That article was dated 2016, but it has all the basics. They were talking about monitoring cylinder head and exhaust outlet temps, which is a bit more sophisticated than the older light Pipers, Grummans, and Cessnas. The only thing that could be added would be P-T diagrams showing the auto ignition regions.

Ah, the fuel test cup. No water, check. Right color, check. Wrong fuel = bad day in an aircraft.

 

Well, I'll chime in, most importantly with a question.

I did read the various "fuel" pages in the manual (2014 GLK base). Yes, there is a blurb about (I'm paraphrasing):
"if you must use Regular, only fill what you need, then be sure to fill up with Premium at next opportunity"

Another section mentions "only use Premium, otherwise the catalytic converter(s) could be damaged"
(an expensive side-effect)

... so here's my question:

Why would a manufacturer specify the use of Premium - it's not like they are getting a kick-back from the gas companies ??
.

 

I'd guess it's because the engine is making significantly less horsepower at full throttle with regular. And who wants their customers to be driving around in their brand's cars that are missing 20-30 horsepower?

Maybe another way to phrase that is "because they can claim significantly higher performance for their vehicles by slapping a "premium only" decal on the gas door (since they can tune the engine appropriately to extract those extra horsepower while using only hardware capable of less power if they didn't have that decal". But that's just a SWAG.

 

I wonder what the rationale is for that?

Don't get me started on aircraft engines. I'm a retired A&P and my last job was teaching up and coming young A&Ps at the local Community College...

 

That doesn’t even begin to make sense.

I even saw a post from a supposedly educated member of another forum who said that regular gasoline contains more sulfur and lead, creating unwanted combustion products that plug up the converter.

Complete BS.

2015 Tier 3 US federal regulations apply equally to all grades of gasoline: 11 g/kg sulfur and 0.0026 g/liter lead.

 

...
That's not my opinion - as I stated, I'm paraphrasing out of the manual, and just to be clear, here's an image of that page I snapped 10 minutes ago




And I found this explanation at this link - I'll post the full answer here, so you don't need to hunt for it

https://www.quora.com/How-does-the-u...grade-gasoline
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----- quote -----
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As many others have previously stated, low octane fuel doesn’t directly affect the catalytic converters!
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The running of lower octane fuel than is called for by the vehicle manufacture radically affects the combustion and complete burning of as much of the fuel as possible.
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I’ll try to explain this in terms as easily understood as I can without getting too technical.
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If you have a vehicle that calls for premium fuel (92 Octane or above) you obviously have an expensive car with a high compression engine. Higher compression is a quick way to increase the volumetric efficiency of any engine, though that comes at a cost.
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The main cost is that if you try to “cheat” and run lower octane fuel, you’re subjecting your engine to pre-ignition. What is pre-ignition? If you ever were driving up a hill and heard your engine “pinging”, which is actually a rattling sound, you’re experiencing pre-ignition. WHat is actually occurring is the fuel is being ignited prior to the spark plug firing by excess heat in any miniscule spot of the cylinder, and the noise is generated by the collision of two opposing explosions within the cylinder. If you research this online I’m confident you can find videos that do layman’s term justice explaining exactly what I am trying to explain.
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Now, when you experience pre-ignition in a modern electronically controlled engine, the ECM is going to automatically retard the ignition timing, which is going to cost you dearly in miles per gallon, as that is going to plummet costing you more right off the bat….. the reason for this is you’ll be harder on the throttle and on the throttle longer than you would be if the ignition was allowed to operate as programmed.
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Due to your ignition now being retarded, you’re definitely not going to be burning the fuel as efficiently as normally. This is going to force the ECM (computer) to begin to remove fuel, or lean out the fuel mixture which is going to worsen the timing issues, compounding your issues. With an excessively lean fuel mixture, your long & short term fuel trims are going to tend to latch lean, which is going to create a hostile environment inside of your catalytic converters.Running that lean you likely would fail any emissions test as your NOx (Oxides of Nitrogen) are going to be way high as the converters won’t be able to clean up all of the NOx that’s occurring due to the increased cylinder temperatures.
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Now, I can get into all of the destructive forces occurring within your engine due to lower than required octane fuel, but that’s not the question.
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The long and short of this is to run the fuel the vehicle calls for. If you can’t afford to do that, then sell the vehicle as it’s only going to cost you substantial amounts of money and ultimately lead to numerous potential catastrophic failures, your catalytic converters being just one small piece of that puzzle.
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Leaning of fuel , incomplete burn , is bs . I’m running regular , mpg is the same , your engine burns fuel completely with high octane or regular, the computers make sure of that.

Knowing you can hear knock if it occurs make sure you don’t hear it. The knock sensor retards timing if knock is detected. I might notice a slight reduction in power if I step on it, but it’s not honestly something I notice , I don’t race it. I do not see any valid argument against regular as long as your vehicle does not knock.

 

Calder-Cay,
I'm not criticizing you. I didn't doubt that the statement was there in the manual. I usually agree with what the MB designers and engineers have to say about our cars. But there is no basis that I can find to support this one. If they were referring to "Top Tier" fuels versus fuels in other tiers, then it would be valid, but not for regular vs premium.

BTW - My BS call was referring to the statement the statement claiming that there was a difference in sulfur and lead content between regular and premium fuel.

 

I've also seen zero difference in MPG between premium and regular (in my Acura and BMW). Just did the second fill-up on the GLK, and this time she got regular (and will for the foreseeable future). I'll let y'all know if my engine melts. ;-)

 

My Volvo XC90 manual stated that premium was recommended but regular was acceptable. They further recommended premium if towing. I ran it 100,000 miles on regular and 3,000 on premium (towing). Never noticed a difference between the two, but then I wasn't clocking 0-60 times or anything.

I did end up selling it when, at 190,000 miles, it needed two new converters, but I think that had more to do with the oil consumption (> a quart every 1000 miles) than the grade of fuel.

[Edit] This just occurred to me: if running regular fuel is bad for the converters, wouldn't that be true of cars designed for regular, too?

 

I used regular gas for a few months when the gas prices went bonkers up here. The GLK350 is my work vehicle and usually full of renovation tools. I don't drive it hard. I did get noticeably lower mileage and power.
I've used regular in my Subaru SVX on occasion and it seemed to make no difference at all. I put very few miles on it though so it's not really a good test platform.

 

If literally Anyone else posted this, you would have a field day calling them every adjective you could think of 🤣

 

My lexus manual says premium while it's running toyota engine used in tundra/sequoia/land cruiser that run on regular. The only time I saw an improvement in MPG is when I used non-ethanol fuel.

Some cars are much more sensitive to fuel than others. I recall reading an article where running cheaper fuel offset any savings by worse mpg. I had a few tanks of regular in GLK and haven't noticed any difference.

I think manual statement in the manual has more to do with not running leaded fuel, which destroys cats.

Regarding un-burnt fuel...every time the car started when cold there a ton of un-burnt fuel going into exhaust (with extra oxygen from SAI) while burning up to warm up the exhaust. Stand behind your car for the first 2 minutes after start up. That's actually an issue on some cars as un-burnt fuel creates other issues in the cylinders.

 

I remember reading a thread on how low quality fuel actually stored something called "Low quality fuel detected" in the ECU, as for what that does I have no clue. It automatically clears once high octane fuel is used again for a few cycles. I need to find that thread again.

 

That would actually make sense in a supercar, or at least something that pretends to be one. Yes, if I own a Ferrari I'd want it to tell me that it was incapable of performing like it is capable of performing. But on a mid-size SUV? I only want to get that warning if I attempt to burn recycled cooking oil. ;-)

 

It is not a warning, but it is stored, I found the thread for you to peruse (if you want : ): https://mbworld.org/forums/gl-class-...ml#post8597849