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Hi all this is something that i though i might share and see if people have seen this before. my 98 E36 328i has a little trouble starting when first cold. not i am not here to ask for help on this but to rather share something i have noticed. i usually run it on 98 octane (Australia’s top of the range premium) and last fill up i decided to put in 95 octane and i have noticed that the car starts a little easier when cold. normally i would have to crank it it would cough then die and on second crank it would start easy or i could start it and blip the throttle are it would smooth out. since i have put in the 95 octane i have not needed to give it a second crank it just starts and after 2-3 seconds it smooths out like it would on second start or blip of the throttle. now i have been trouble shooting this for a while and im down to having my mechanic check fuel pressure and flow as-well as do a quick diagnostic check when i take it in next. i have done all the basics and double checked everything. has anyone seen this before that a change in octane allows the car to start or even run a little better. now it appears to start easier but it could be a placebo effect on my behalf. i am familiar with how different octane fuels have different ignition points and that 95 is more potent than 98 . im am interested to hear peoples thoughts on this.
cheers
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Could be you were getting poor quality 98 octane. Usually premium sits more than regular here in the states anyway so you may have gotten some with water in it.
Using a higher octane rating fuel than recommended by the MFG is a wast of time, money and bad for the environment. Engine computers that are designed for as specific Octane will not perform better nor be more efficient on higher octane fuels. In fact will generate more pollutants.
Higher octane is one of the most misunderstood concepts in cars.
Simply stated… higher octane fuel is less explosive (or more accurately, slower burning) than lower octane fuel… which totally goes against what most people’s conceptions are..
High octane is required in cars which have high compression engines… which is why most performance cars require it… this is where I believe that the misconception starts…
If lower octane fuel is used in a high compression engine, then the fuel explodes before full compression can occur, causing knock and diminished performance.
Higher octane fuel can be used in a vehicle that calls for regular fuel, but as stated, it is just a waste of money… any benefit is usually psychosomatic in the person who does this…
to the OP. I don’t know if your vehicle requires high octane, but if it doesn’t, you are throwing money away… if it does require it and runs better, the only thing I can surmise is that your compression may be lowered to the point where regular fuel runs better… but as I said, this is just a guess. ..
Karl
the only benefit you can get from running a higher octane with a engine with the stock compression, and no increase in boost, is you can advance your ignition… which only does so much, stick with what the manufacturer recommends.
in my case however my cars ignition system i have noticed does advance spark, so i can get a little gain i torque with higher octane fuels, but there is only so far it will advance ignition, and only so much of a gain which really doesn’t make it worth it.
#13aceofspades13
I’m no expert by any means but to my knowledge an advance in ignition timing should cause a decrease in cylinder pressure and a decrease in torque but higher octane fuel burns slower so the net power will remain essentially the same. If you can quote an authority (scientific proof) of your theory I would appreciate a link so I can read it.
Some cars have a low octane spark map and a high octane spark map and they usually have a merging effect when the computer relearns depending on manufacturer and engine. BMW tends to use higher compression so they usually advise use of premium fuel. I think water got in the fuel imo.
After working in the industry installing monitoring equipment in these tanks I can assure you the filling stations have no desire to sell gasoline with water in it and the suction tubes are approximately four (4) inches from the bottom of the tank to avoid sucking water off the bottom.
Also, the absolute worst time to fill your tank is when the tanker is there for a fuel dump or just after. Filling the storage tank causes the water in the tank off the bottom and mixes with the fuel; as a result there is a greater risk of getting water in with your fuel.
Filling stations routinely have the water removed from the tanks to minimize the fixing affect during a fuel dump, but it still does occur as it is impossible to remove all the water out of a tank once in the ground.
The highest octane fuel tank is typically the smallest one installed (3000-5000 gal), since as mentioned it does not sell in the quantity as the lowest octane fuel. The other little know secret is the modern pumps blend the lowest and the highest octane fuels to make the mid grade as it pumps. This it typical on pumps with one hose and three buttons to select the grade of fuel.
Where I live it’s quite common to get water in fuel even though I live essentially in a desert. Hot arid climate. I think it’s due to the ethanol. Since every station here has ethanol in it. Depending where you live you may have no ethanol in the fuel. But mostly I see ethanol and ethanol likes to collect water. So that could be why he was having those issues.
Have you had much luck using a fuel stabilizer in the tank to nullify the affects of ethanol blended gasoline?
I use Marvel Mystery Oil in my vehicle; 4 ounces per 10 gallons of fuel.
[quote=”Jotmon1″ post=150519]#13aceofspades13
I’m no expert by any means but to my knowledge an advance in ignition timing should cause a decrease in cylinder pressure and a decrease in torque but higher octane fuel burns slower so the net power will remain essentially the same. If you can quote an authority (scientific proof) of your theory I would appreciate a link so I can read it.[/quote]
quite simple, done in performance cars all the time, advancing the ignition timing pushes down on the piston sooner causing a increase in power, you can increase your ignition timing too far and cause knock. Mighty Car Mods made a car called Gramps, it was a subaru Liberty station wagon with a 6 cylinder boxer engine and a turbocharger, before they upped the boost they decided to make a change to E-85… when they tuned the car for E-85 they didn’t add boost they simply advanced the ignition and got a increase in power just from advancing the ignition timing!
Now E-85 being a higher octane fuel than 93 octane pump gas, means naturally you want to advanced the ignition because it burns slower than the pump gas. when they did this they gained power, then they added more boost and got even more power, once again they do this all the time, and a lot of there cars the ECU adjusts your ignition timing, however like i just said the gains are so small in many case it isn’t worth it, run on what your car recommends.
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