Fitchick

I am looking at replacing my 2008 CLK 350 (hit by uninsured motorist and totaled)
anyway, I babied my car had only 51K and used 91+ fuel.
I do not want to buy new. If I purchase a used car there is not guarantee that the former owner(s) used high octane gas.
Question: What kind of damage can be caused from using low octane and is there a way to reverse damage or "clean out" the engine from the use of low octane?

Thanks

Cambridgehank

Check this out.

kajtek1

Low octane gasoline cost engine pinging when under heavy load.
That in modern engines is prevented by knock sensors, who will give signal to computer to adjust timing.
Meaning occasional use of lower octane should not leave permanent effects (assuming the car is not raced) but long-term effect on engine operating with marginal specifications are hard to determinate.
Buying used car is always a gamble to some degree and in the past I did not hesitate to run compression test.
Such test on modern engines, where sparks take long time to get to becomes very difficult, but then moder scanners run "smoothest test" that will indicate when some cylinders have different compression than others.
Don't buy used car without one of those scanners.

Fitchick

Thank you for the advice.
Very helpful!

Lolxa

If your thinking of using 87 octane gas instead of 91. For my 2010 E550 4Matic. For the first 2 months, I didn't care about the difference of gas as I believed they were all the same. But I learned the engine was rather running rough on 87, when in park idling, you could feel tiny stutters. This was eliminated by using 91. Just a thought if you wanted to know.

DFWdude

Here in TX, we have 87, 89 and 93 octane gas. For the first 4 years under warranty, I ran my 2001 C320 on Premium. In 2006, I experimented with lesser grades. The V6 did not like regular unleaded (87) at all. Lots of feedback telling me the ECU was not adjusting well. No knocking, just periodic hesitation on acceleration.

However, I noticed no problems using midgrade (89 octane) for regular driving (I'm not a lead-foot). The ECU took 5 minutes or so to adjust, then operation resumed as normal. I operated with 4 tanks midgrade followed by 1 tank premium (when I thought of it) for a couple years without problems.

The apperance of that huge 2007-08 spike in gasoline prices had me switching to midgrade permanently. That was ten years ago, and the car is still performing fine as it always does.

Mud

Good advice from all above. I go back and forth between 93-91ish octane so I guess theres a blend in the tank. I don't drive that much so cost is less of a factor. Car seems to run great.
Buying an off lease (like I did) can always be a roll of the dice. I did a lot of research into the maintenance history but you can't tell what gas has been used, maybe get a hint from plug condition but doubt most will start pulling plugs. However I figured miles were low enough on the car I liked to hopefully reduce any negative impact. I would not buy a higher mileage vehicle just off lease but that's just my risk mitigation strategy.
My overall thought is that a lease vehicle with no plan for later purchase will not be treated as well as one bought outright. So plan your strategy accordingly.

Aktash

if you don't drive too much then price difference between 87 and 91/93 is not that much.
say you drive 20k year at low estimate of 20mpg that is 1000 gallons, at $3.00 average for 87 and $3.45 for 91/93 difference is $450 a year.
not really worth risking long term damage. I think most people fill up with what is required as if something goes wrong your warranty will probably get denied, once the warranty is up and car has had a couple of owners best way to judge is by looking at condition.
If the car is filthy inside especially in those hard to reach places then most likely person didn't care about it, most dealers just do a routine cleaning instead of detailing so that would be a first red flag for me. Same as for habitual wear items, look at seatbelts if they are greasy, like belts themselves and buckles, if person didn't care to shower or clean hands tells you how much they cared for car upkeep. Look at tires type in google their exact name see how much they retail for, because there are good brands cheap tires and good brand expensive tires, if person skimped out on tire performance they may as well skimped out on some maintenance items as well. Things of this nature are what makes or brakes a deal for me.
With used cars you get what you see quite literally and in US most dealers don't bother to hide minor things, giving away car's past care practices.

KEY08

Never understand why people won't put the proper fuel in their car or buy the cheapest and noisiest tires. These are the same people who try to justify the mileage of their V6 vs V8 when it comes out to an extra $200 annually in gas savings, if even that. In terms of this question regarding prior owners using low octane fuel, the poster above pretty much nailed the typical owner of these cars. They cheap out on everything, never bother to wash or clean their car, and have never visited a car forum in their life. Buy from reputable dealers or friends you know who are responsible.

dbldpr

I have never skimped out on what was called for with my cars. I feel that if you cannot afford to get what is needed for the car then you should buy a cheaper car that will take the cheap stuff you put into it. Do not buy a Mercedes just to say you have a Mercedes. If you cannot take care of it properly then I believe you should not have it.. But that is only my opinion.

DFWdude

As always, we continue to have people using the "Cheaping out" value judgment to suggest who is the alpha dog in the pack.

Some of us here can pay cash for any ten, older, ie., "cheaper" ie, second hand cars (W212s), and a couple W213s as well, along with a garage big enough to house all dozen of them. A decision not to buy the only 93 octane fuel available, when only 91 octane is specified -- or anything less -- is a personal decision, not really open to criticism or personal derision.

Such comments always kill thread discussions (this one has not seen a post in 18 hours since the last). So, please keep your value judgments to yourselves.

To be clear, my comments are meant to get this discussion back on track (back on topic), not to start some tit for tat rant with anyone....

MaschioneCazzuto

VegasE

The "average" person drives about 10K a year and I'm getting in the mid-20s on mpg. Bottom line is that you can save more money just buying one less Starbucks a week than you will going with cheap gas.

The best way to clean out the system that has been abused with cheap gas is to use top tier premium fuel. Adding stuff to the gas yourself doesn't have much effect.

dbldpr

Really!!!!!!

People like you are really the ones that cause the thread Kill with a discussion. You are the one that should keep your value judgement to yourself. If we do not think your way you expect us to keep quiet. Well that is not the way it works. Everyone has there opinions. I except yours even though I disagree. If you do not accept mine it is to bad because you have a closed mind and you are very limited.

BillyT293

I'm going to take a stab at actually answering OP rather than ranting on the economics of fuel choice. I thought premium fuel was required because MB engines tend to be designed with higher compression ratios and would be more prone to knock and ping with lower than recommended octane fuels (but correct me if I'm wrong).

I wondered if knock could cause damage and a quick google search found several results confirming it can - apparently it can cause damage to the piston and cylinder wall.

Strigoi

It can also damag crank bearings.

Arrie

It really does not matter what octane you use for the car as what comes to engine health. It adjusts to the octane rating you use. MB advertises to use 91 or higher octane but this is just for the performance and fuel mileage. They do this mainly top keep their carts under some level of fuel consumption as it has effect to the consumption rating that affects the selling price / taxes on the whole line of vehicles they sell.

I have run my car with the 5.5 liter engine many tanks with 87 octane fuel and the only difference is the MPG goes way down. No savings doing low octane. I have not tried mid grade so perhaps I should as most of the time when I buy 91 or 93 as advertised at the pump I feel I'm getting something less.

The point is low octane fuel does not hurt the engine, it just lowers the performance and fuel economy.

kajtek1

Let me line up the facts.
-pinging is harmful to the engine
-knock sensor will lead to timing adjusting to prevent pinging
-the adjustment will happen AFTER some pinging happens
-proper octane gasoline will prevent pinging to happen in first place.

Edward993

^^^ True, but that's not the full story.
1. Any pinging (pre-detonation) that occurs, which gets picked up by sensors, will result in retarding the timing such that the pinging will stop; true. But this does NOT mean pinging is the defacto result of lower-octane fuel. Ambient temp, load, and driver's right foot all factor in WITH octane; change one parameter and it exacerbates/mitigates against the others. Light/gentle acceleration, cool temps, single driver doing mere commuter miles ...these will present ZERO issue with engines --even high-compression, or turbo/supercharged engines-- running on 87. This was true even before "motronics" because these are physical properties that govern pinging; modern engines with the full gamut of sensors and dynamic mapping are exponentially smarter in this respect.

2. Running a modern car (with aforementioned electronic gizmos) on 87 that is designed for 91 will do NO damage to the engine whatsoever If --IF-- the conditions would not create pinging from the get go! Imagine you are simply commuting to work, in sweater weather, at 75mph on the grand flat superslab: your performance engine --of which our E350 most certainly is-- is not even close to being taxed in load or temp; 87 or 91 makes ZERO difference to the engine. None. And should you mash the gas pedal, the "worse" that would occur is the lower-octane gas will cause the engine management system to "pull back" a bit and your acceleration suffers compared to having had 91 in the tank. No damage whatsoever, except to one's ego, perhaps.

3. Change the conditions and yes, octane definitely matters. The above scenario is markedly different in heat, driving up a grade, four adults/luggage in the car, or stomping on the gas to pass a semi. Combine any or all of these, and yes, you'd do very well to have that premium in the car.

4. Do what suits you best. Personally, I fill my wife's E350 with 91, and she's no leadfoot and does easy commuting/in town errands, and we live in mostly mild temps (except for maybe several few weeks in the year). But I use the 91 because you can't predict when "that" situation presents itself, and since it's a performance car, I want it to perform. But that's me. I have no doubt whatsoever that there are more than a few folks who enjoy their luxo-cars at an easy, sedate pace, in moderate climates, who are more concerned with a polished/vacuumed car than racing up Pikes Peak. For them, no issue using 87 -- or perhaps 89 as the better compromise-- as their style of ownership will never reap what 91 would offer.

5. Slightly off topic: may I suggest another important consideration that is not mentioned here is brand of gas. I don't want to go down any rabbit holes here, but the cheap gas out there is inexpensive not because it's bad gas, but because it lacks the detergent additives that the big brands mix in. Hence, the cost of "better" gas is no marketing snake-oil scheme: detergents/additives cost them, both in material and R&D. So I fill with Chevron, and Mobil as an easy backup, whenever I can. I am not draconian about this, but merely being proactive as one who keeps cars as loooong as I possible, and so longevity is big with me. Lease and turnaround guys: feel free to ignore this as you're getting a new ride often enough, so enjoy!

Edward

Tump43

All of the above, especially #5 is spot on, correct. With my direct injection 2014 E350 I use Top Tier gas (there is a thread on this board listing all the top tier brands), i.e. gas from a co. that has it's gas certified to provide a certain level/quality of detergents, these are generally the big name stations. I'm not so concerned with octane, but generally use 91 because I'm prone to aggressive acceleration, when mellow over long highway trips, 89 will do just fine.

Arrie

So, little thinking on this,

Diesel engines are direct injection for the fuel detonation at the right moment. They now make gasoline engines with direct injection meaning that if the fuel is introduced in the combustion chamber at the correct moment the lower octane fuel should bring better fuel economy / performance as the lower octane fuel does not have chemicals for retarding the self ignition>

Tump43

But direct injection gasoline engines still uses spark plugs (not glow plugs) and are still subject to pinging or pre-detonation in high compression engines as are the 2012+ E350 engines. This is why Benz requires a minimum of 91 octane for GDI (gasoline direct injection) E350 engines.

But, I was talking about the quality and level of detergents in the gasoline. Since the injection passages in GDI engines are that much finer, small build up of crud/carbon from low quality gas will negatively impact performance. This is why top-tier gas is recommended. Also, some lower octane versions of otherwise top-tier brands don't carry the top-tier gas certification.

Arrie