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What gas?

3K views 35 replies 16 participants last post by  limelight 
#1 ·
Do you guy's burn Premium gas in your s 420. I know it say's so on the fuel guage and in the owners manual, But is it really Necessary? The last car I had that really needed premium was a 1968 muscle car with a big block motor. I've been putting premium in, but I'm just wondering if it really makes a difference.

Thanks, Mel
 
#2 ·
I guess you could use either.. I take it that your S420 is pre-1995?

I have used both kinds of gas in my S320, leaded (premium) and un-leaded (new cars).. Cant say I felt ANY difference between the gas milage or performance..

It is only harmfull for newer cars to use premuim gas, since it can damage their O2 sensors and Cats.. But the car would still drive regardless..

Your car would be safe to use either or.. Just try both, and see which one "seems" better for you..
 
#5 ·
I forgot to say the year, It's a 1998
Since it is a 1998, use (un-leaded) gas.. Im not sure what it is called where you live, but its the one that ALL new cars run on.. Im sure you do have O2 sensors and CATS on your S420, so you would not want to damage those..

Best of luck comrade!
 
#6 ·
Use premium unleaded if you really care about your engine internals. lol. As soon as my shop gets moved, I am buying a small tanker to keep a 98 octane unleaded in--a bit pricey for most people ($8.50-9.00 per gallon), but beyond worth it in my opinion as US gas is complete $hit.
 
#9 ·
I'm not sure if octane ratings differ, but at Agip and a few other stations in Europe I can find 99 :D I use 98 or 110 (leaded) in the race cars. I've found the higher octanes, such as 93 and 98, burn much cleaner than the regular 91 crap that's sold everywhere. My head MB tech says that the 91 clogs up the M120s very badly. He says the whole fuel system goes to hell due to the poor quality. Unfortunately all the cars have had to suffer through using it as I haven't had any place for a tanker. The new dealer has a huge parking lot though so I'll finally be able to treat my cars better.

Fuel debates are like asking what brand oil or tires. I swear by Michelins, Mobil 1, and high octane. There are other people that buy "generic tire #2," use Penzoil, and fill up with 87... It's all up to what you feel like in the end I suppose.
 
#8 ·
Premium is better for your engine. I read somewhere that it provides better combustion, and less chance of detonation or nox or something like that.. At least thats been my experience with forced induction aplications
 
#11 ·
There is a gas station in the middle of no where farm land, about 25 miles out of my town, I go there to fill up before the races. 98 octane :thumbsup: only one with an octane rating that high that I've ever seen around here
 
#14 · (Edited)
I needed petrol the other day and by accident filled it with 95 octane petrol ,by the time i saw the 95 on the pump i already had 50 dollars in, that's where i stop't , i said to my wife listen to the engine any second now & bang about 200 metres down the road it happen'd, she could'nt belive it when the 95 petrol came trough ,the engine started a slight missfiring and did'nt sound to good ,i just turn't around & back home there i drained it all out ,havn't driven it since , that was last week.
I try to do a little video of it to let you guys hear the change of engine sound what difference it is with 95 & 98 on the 5.0L v8 since i still have the 95 petrol in what ever is in the fuel pipes ,i go and get a 20L tank and fill it in the garage with the 98 octane Mobile before i take her out again . This is the 2nd time i got bitten ..............
I think i saw here on the forum in some post's that some members had there EZL changed or a slight modification to run the car on a lower octane rating .
 
#15 ·
I would use premium. It really doesn't cost that much more in the end. :)

It's a 26 gallon tank. 7-8 bucks more every fill up?? Then again if I wanted to save gas I wouldn't floor it from the stoplight everytime haha

-Z
 
#18 ·
sigh, lot of misconceptions and wives tales here.

1. The octane in other countries is generally measured with RON (Research Octane Number). In the united states, its measured with R+M/2, which is RON+ MON (motor octane number). The RON will be a higher number. So when a guy in germany says he runs 98 octane, its no better than the 93 here.

2. A car will not misfire or run like crap on 87 or 89 or 91. The only time this makes a difference is when you heavily load the motor, at which point the engine may pre-ignite or detonate, and the knock sensors will pull timing. At part throttle, you should really notice very little difference. Gas mileage may be slightly lower on the lower octane stuff.

3. Higher is not always better. An engine tuned for 93 octane will not run better or make more power on 100 octane. In fact, it will generally make less power. If you tune for the higher octane stuff, then obviously you see a power gain.

4. There are some fuel additives that contain enough MTBE to make a difference. Lucas makes a octane booster that has shown to work, and Torco works well. The trouble is that its not cost effective unless you have absolutely no source for the higher octane stuff from the pump.

The bottom line is that you can run 87 if you don't often go full throttle. It is not lower quality and won't gunk up your valves or anything else. It simply does not have the octane increasing additives. Furthermore, you have less of a chance of getting bad gas because the 87 gets purchased far more frequently, resulting in more turnover.

An idiot gas station attendant put 87 in my 911 turbo. The car ran fine and I just stayed out of the throttle. No problem.
 
#20 ·
sigh, lot of misconceptions and wives tales here.

2. A car will not misfire or run like crap on 87 or 89 or 91. The only time this makes a difference is when you heavily load the motor, at which point the engine may pre-ignite or detonate, and the knock sensors will pull timing. At part throttle, you should really notice very little difference. Gas mileage may be slightly lower on the lower octane stuff.

3. Higher is not always better. An engine tuned for 93 octane will not run better or make more power on 100 octane. In fact, it will generally make less power. If you tune for the higher octane stuff, then obviously you see a power gain.
Maybe for you it dosnt but mine certainly misfires once the crap petrol comes thru , just wait when i make that little video and it works out to be heard , also the engine behaves verry rough you can see it shake not much just a little , i show you just hang in there ,i dont say it missfires for nothing you know ,i know my car ,she drives flawless, never misses a beep only when mistakes like this happen with the 95 octane ,mine WANTS 98 nothing more nothing less , i know it sounds weird what can i do ,unless they added some of that ethanol blend into the 95 tank (?) ,i know some stations mix there petrol or whatever to make more money ,i only use either Mobil or Shell last time i used Ampol (only because the wife said to stop there ,she copped it later for suggesting it to me ).
No need to respond yet ,you'l be sorry trust me ...........
 
#19 ·
yeah that sounds about right, you can run 87 in turboed cars too if you dont boost very hard. just stay off the pedal

the octane differance is interesting, I was always thinking the europeans were lucky lol
 
#21 ·
The stickers on the tank and dash indicate premium. With a billion in engineering and developement costs you have to believe they know what is required. It only costs about 10 cents mor a gallon. And remember these are fairly high compression engines by todays standards. Back in the day 100 octane was premium and what we call premium today was regular then. It is only through modern fuel management and head design that w can burn this low of an octane in these engines--like I said, this car was engineered to burn premium.
 
#25 ·
Thanks for that info about RON and MON OliverK.

From what I understand and remember reading somewhere, the engine will absolutely run 87, but not efficiently, right? Do you know what kind of power loss we are looking at for each model? Also won't it first knock a little bit until the car tries to adjust itself?

-Z
 
#26 ·
Its just gas...

I use premium because it makes me feel comfortable.
I know that if I use 87 octane that my car will NOT blow up, die, dissappear, fall apart, or catch fire... I've never noticed a differance between running 93 as opposed to 87 except for in cars with turbos. If your foot is down with a boosted car then it seems to stumble a bit at higher rpm.. but not much, and not enough to make your QM ET's much slower
 
#27 ·
Octane rating is a measure of a fuel resistance to burning (essentially). Use of 87 octane is fine and will not cause any loss of performance if there is no detonation.If you drive moderately with a lot of cruising and little full throttle action then you will be fine.If cylinder pressures climb to a level high enough to cause detonation, then the engine computer will see this through the knock sensor readings and retard ignition timing until the detonation stops and then slowly add it back in as pressures go down.This is the reason you can use regular in these vehicles without damage.Now gasoline detergency is a whole other matter.....
 
#28 ·
gas

Wow,
The reason I started this off is I have a 2000 ford F-350 power stroke diesel, A few years ago I had to replace ONE injector. The shop said I should be using a additive. I've put 40,000 on the motor since, and still have only replaced ONE injector. It seemed odd that only one injector was bad from so called bad fuel. So since we just got the 98 S 140 with 122,000 and every receipt since day one. None of which were bad fuel related, and my father in law, the original owner always burned regular fuel, I wonderd if it really matter's. I'm going to burn premium anyway.

Mel
 
#29 ·
^:thumbsup:
 
#31 ·
On forced induction vehicles, the engine compression is pretty low.
All forced induction vehicles "require" premium fuel, that is because the turbo/supercharger makes up for the lower compression. Would that be correct?
 
#33 ·
Thank you OliverK
 
#34 ·
You should always use premium when it recommends it. These engines are 10:1 compression (at least I know that for the V8's) The higher octane gas burns slower and resists combustion from pressure better than lower grade gas.

In the case of an engine that doesn't need premium fuel, using it is not good. Because it burns slower, engines that don't need it, low compression engines for example, the gas doesn't fully burn and will dirty your engine more if you don't drive hard regularly.
 
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