How many of you run 87 octane fuel?

[beegeezy]

I usually run 89, and occasionally a tank of 91. I can locally get 87,89,91,93,and 100 at the pumps. If I go inside the gas station I can get 110 unleaded. Boost on 10:1 compression ftw!

[Letsplayskatch]

RON ratings are only an indication of the fuels ability to resist 'knock' (i.e. detonation, pinking etc). Power gain from using such fuels is pretty much non existant.

[sheepdog]

Without a chip, I can tell when I have poor quality 91 in the car. I lose mileage and performance. I only run 91 from a better rated gas company and 93 from others unless I am in a pinch.

The manual states 91 octane.
110 is overkill and you are actually doing damage to your cat by doing that.

[sheepdog]

RON ratings are only an indication of the fuels ability to resist 'knock' (i.e. detonation, pinking etc). Power gain from using such fuels is pretty much non existant.

It depends on how you look at it. A simple statement like that is incorrect due to the number of assumptions that can be made from it.

RON is actually burn speed. Higher octane burns slower. A slower burning fuel may not fully fully burn sending raw fuel into the catalytic converter where it is burned off. Too much and it destroys the cat. A lower octane gas in a car detonates or burns too fast, this can make you lose lots of power and damage a piston or valve or bearing.

Power benefit depends on how you look at it. If your car is timed for a slower burning fuel (like 91) and you put 87 in there, you can lose a lot of power. However putting 91 in a car meant for 87 does little.

I had a Toyota that would get 5-6 mpg better with premium. When I figured out the mileage vs fuel cost, it was cheaper to run premium by $2 per tank.


Bottom line, run close to what the manufacturer tells you. You can vary a little, try tracking mileage to see what is giving you the best burn. Whichever gives you the best mileage is what the engine prefers. This will be close to what the manufacturer recommends usually.


I would not try 87 in a car meant for 91, that is too large of a jump. 89 will probably the lowest you should go.

[beegeezy]

Oh im not running 110 in my car. I run 89 or 91 usually. But its nice to know that I could boost the m42 on stock compression . If im willing to pay about 9-10$ a gal....

[nomad]

I filled up a year ago and am still burning it off.






Filled up the day the head gave out!

[Letsplayskatch]

^ Fuel has a shelf life. All dependant on the quality of the fuel really, depends where you got it from and what additives they use.

RON is actually burn speed.

Sorry, it isnt. Burn speed is known as the Flame Kernel, and its a different matter entirely. RON means Reasearch Ocatne Number, and it denotes the petrols knock resistance. For lack of a better source, check wikipedia if you think im wrong

Petrol itself is a very good knock-inhibitor. Stripped bare of any additives, the actual chemical formula of petrol does well agianst fighting off knock. Once we throw additives like Octanes [and therefore 'octane ratings'] into the mix, then we begin to increase the fuels knock capabilities.
 Dont confuse the term 'octane' to how much 'oxygen' that you think is in the fuel [which people associate with providing a cleaner, more powerful combustion] like many do. Octane has the chemical formula C8H18 (Carbon8Hydrogen8). Iso-octane is a branched hydrocarbon, and is used to define a fuel’s octane rating. It has excellent anti-knock ratings and is highly desirable in petrol - it isnt a form of oxygen in any sense of the word; and thus has no power-increasing characteristics.

Also, as Octane ratings are all about knock-resistance I should mention that fuel injected cars need a way of sensing/detecting knock in the 1st place...hence knock sensors:

I had a Toyota that would get 5-6 mpg better with premium. When I figured out the mileage vs fuel cost, it was cheaper to run premium by $2 per tank.

Seeing as pretty much every Toyota comes with knock sensors, youve just proven my point Your Toyota advnaced its ignition to take advantage of the higher anti-knock capabilities of the fuel. Which, in-turn, gave you better, more cleaner ignition = fuel savings...and a tincy-tiny powah increase.

BTW people, the M42's dont have knock sensor...so all of this is kind of pointless. Without knock sensors, 'premium' fuel is just a waste of money.

[sheepdog]

Seeing as pretty much every Toyota comes with knock sensors, youve just proven my point Your Toyota advnaced its ignition to take advantage of the higher anti-knock capabilities of the fuel. Which, in-turn, gave you better, more cleaner ignition = fuel savings...and a tincy-tiny powah increase.

BTW people, the M42's dont have knock sensor...so all of this is kind of pointless. Without knock sensors, 'premium' fuel is just a waste of money.

Timing advance on a 1979 Toyota, I don't think so.

If premium was not necessary, BMW would not have put it in the manual that it is required. There is at least one or 2 people on this forum who have had their engines fail by using incorrect fuel.

Go ahead if you want, personally I am not going to risk it to save what amounts to an extra buck or two per tank, especially when I can feel a difference in how the car runs. More power or not, the car does run better.

[Cobra Jet]

Interesting replies...

I started this thread because prior to my 91 318ic going down on a non-start issue (that thread is in the appropriate section on here) - I was successfully running 87 octane with NO issues what so ever...  Meaning, I did not have or experience any pinging, no knocking, no pre-ignition, no drivability issues, etc etc etc.  As a matter of fact, out of a completely full tank of 87 octane gas, I was able to go 384 miles out of my last tank - no BS.  I've read on other forums about other BMW owners of E30's, both 318's & 325's also using 87 octane with no issues at all.

Now, I don't flog on the car at all - meaning, I don't jump stop lights, I don't try to race others on the highway, I don't speed shift, I don't do WOT runs up and down the streets, etc.  I use the car in a normal manner - driving to & from work, shifting it right before 3k, running errands, etc.  My daily commute to & from work, total round trip is 114 miles - 5 days a week.

Sure, the owner's manual may state to run "XX" octane - however, just because the manual states to run "XX" octane does not mean the car will not run on lower (or higher) octane fuels.  Heck, I even run 87 octane in my Cobra - when the manual for that also states to use 91 (or better) octane - that car runs flawlessly as well.  

Understandably so - if one has a highly modified engine, be it a naturally aspirated engine that has been radically bored out, heads, intake, cam, exhaust, etc., OR if running a forced induction vehicle (supercharger or turbo), OR if the vehicle has been "chipped" then surely I can see that such a vehicle would HAVE to be on a strict higher octane "diet".  But, if all you are doing is driving your 318/M42 to and from in a normal manner, the car will get nearly the same mileage (maybe even better) on 87 octane AND it will operate, idle, drive & run perfectly fine.

I previously filled the tank 3x now w/ 87 octane - each end result was 378, 381 & 384... and the gas gauge needle was just about resting on the "R" - the gas gauge low level light never illuminated for any of those prior fills... (the low level light DOES work, because when I first bought the car it only had a little gas in it and I ran it down to the point of when that light kicked on).  

I had read online that when or if the low level fuel indicator light does come on in a 318/M42, the driver/operator has about another 12 miles to go before the tank is COMPLETELY EMPTY (or in danger of running out of gas).  If I were to run the car to that point on the last result of 384 miles, I realistically could have tallied up 396 miles on a tank of 87 octane...  That's damn close to 400 miles on a single tank of gas - good or bad?

Oh and one more thing - don't go busting my chops about running the car low on gas - I've heard all of the myths, stories, threads, etc as to "sucking up tank debris, etc" if running the tank or pump below 1/4 tank...  I've run every car I've ever had down to nearly the "last drop" and I've never once had ANY vehicle EVER burn up a fuel pump, suck shit into the engine, etc - NEVER.  Let me also add there is NO WAY the fuel pump COULD suck up anything into the engine if running the tank low because: 1) The fuel pump has an extremely fine mesh screen (or commonly known as a sock) on the bottom of the pump which prevents ANY debris from getting sucked up into the pump OR fuel lines and 2) the fuel filter also filters out any impurities and/or mirco particles that *might* get past the fuel pump's screen...    Don't believe the hype - sure it's ok to take precautions, but seriously, running the tank down to 1/4 or less is NOT going to hurt anything (IMO).

Now, back to 87 octane - for those running a non-modified M42 - fill up with one tank full of 87 and drive the car normally - post back here w/ your results/observations, etc.  If you're driving style is that of Mario Andretti, don't even bother...

Now, there are numerous things that COULD and CAN affect fuel consumption:

1) driving style
2) duration of travel
3) highway or local travel
4) preventive maintanence of engine/vehicle (checking things BEFORE they become inoperable)
5) tire psi inflation
6) regular maintenance of engine or driveline (oil changes, fuel filter, air filter, pcv valve, injector cleaner, tire rotation, brake wear, wheel/hub bearing wear, tranny fluid changes, rear diff fluid changes, etc)
7) driving w/ windows open (changes aerodynamics of vehicle)
driving w/ A/C on
9) speed limit of vehicle over a prolonged traveled distance
10) geographic location (above or below sea level)

I'm glad to see the above responses, because I was just curious to see how the thread would progress knowing that I myself do run the 318ic on 87 octane (and that others have or do as well).

Keep the conversation going!

[Cobra Jet]

There is at least one or 2 people on this forum who have had their engines fail by using incorrect fuel.

What members had engines fail due to FUEL issues??  I personally do not see how using any other octane other than what is stated in the BMW user Manual that by doing such would cause a catastrophic engine failure.  There had to be other issues that led up to the engine failure.

What are the other facts based on those failures?  What was the long term maintenance history of each engine prior to failure?  How many miles on each?  Etc....

If the cylinders were being washed down (dumping fuel), sure, this would eventually cause a failure due to washing out the bearings as well (dilluting the normal oil lubicration properties) - however, that would not be caused by running a lower octane fuel as there are many other factors that would cause cylinder wash out...

Where are these threads - as I want to read them.

Like I said, I've seen other threads or posts not only on this site but other BMW sites where folks have successfully used 87 octane w/ no adverse effects.

[John W]

I have an aftermarket chip so I always use premium. But I would use premium even with the stock chip.

The reality is that you're probably not going to cause major engine damage if you drive mildly and use a less-than-recommended octane. (Let's face it; you're much more likely to have to deal with a major engine repair due to wear of the M42's timing components or having a bolt sucked out of the upper oil pan.)

But the reality is also that long term you're going to see driveability problems due to things like excessive carbon buildup on the valves or a failed catalytic converter.

These days, I spend too much time at work to work on my car as much as I'd like. So I want to eliminate as many problems as I can before they begin. I've also cut back my driving considerably over the past several years and am now down to about 8-9k miles/year. Cutting your miles traveled in half (or even by a quarter) will save a lot more money than buying lower octane fuel.

Higher gas prices are here to stay and for all but the rich we're going to be forced to make some major changes in our driving habits as prices continue to rise.

[tjts1]

Timing advance on a 1979 Toyota, I don't think so.

If premium was not necessary, BMW would not have put it in the manual that it is required. There is at least one or 2 people on this forum who have had their engines fail by using incorrect fuel.

Go ahead if you want, personally I am not going to risk it to save what amounts to an extra buck or two per tank, especially when I can feel a difference in how the car runs. More power or not, the car does run better.

I wouldn't indiscriminately run this engine on 87 octane when the intake temperature varies between 122-158f while the ambient temperature is 64-82f.

BMW specifies 91 octane because the engine was designed with an extremely hot air intake. Fix the intake and you can safely use 87 octane.
http://www.m42club.com/forums/showthread.php?t=5561
Anybody can use the outside temp sensor to check the temp inside the airbox.

[sheepdog]

Now, I don't flog on the car at all - meaning, I don't jump stop lights, I don't try to race others on the highway, I don't speed shift, I don't do WOT runs up and down the streets, etc.  I use the car in a normal manner - driving to & from work, shifting it right before 3k, running errands, etc.  My daily commute to & from work, total round trip is 114 miles - 5 days a week.

Sure, the owner's manual may state to run "XX" octane - however, just because the manual states to run "XX" octane does not mean the car will not run on lower (or higher) octane fuels.  Heck, I even run 87 octane in my Cobra - when the manual for that also states to use 91 (or better) octane - that car runs flawlessly as well.  

If you read your manual you will find your way of driving your 318 is not good for it. The manual tells you you need to get it up above 3k regularly. In fact they give a ratio of how much above and below you should spend.

These cars were meant to be flogged, not granny shifted.

As I said, am sure you can get away with it, but it is not worth it to me. Too much risk.

I had read online that when or if the low level fuel indicator light does come on in a 318/M42, the driver/operator has about another 12 miles to go before the tank is COMPLETELY EMPTY (or in danger of running out of gas).  If I were to run the car to that point on the last result of 384 miles, I realistically could have tallied up 396 miles on a tank of 87 octane...  That's damn close to 400 miles on a single tank of gas - good or bad?

I have no idea about the 12 miles, but if that were true, I would have just been on fumes. Most cars with a light like that come on around 1-3 gallons left.

[sheepdog]

What members had engines fail due to FUEL issues??  I personally do not see how using any other octane other than what is stated in the BMW user Manual that by doing such would cause a catastrophic engine failure.  There had to be other issues that led up to the engine failure.

Not sure who it was, but the rod bearings took a beating. Apparently nothing else was too bad. Normally these engines do not go through bearings.

Just because you do not hear pre-ignition does not mean it does not exist. By the time you hear and notice it, it is is pretty bad.

Maybe one of them will chime in.

[PaulC]

Been running 89 AKI in my stock motor for the past few hundred miles and haven't noticed any pinging or change in performance.