Re: e23 Average Gas Mileage? (archive)

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One more time, your E23 is designed for 87 octane, and will get the best mileage - and performance - on it. Without loss of generality, the lower the octane number, the more energy per unit volume of gas. Higher compression motors need the higher octane to avoid pre-detonation. I believe the M30 is 8.5:1 - pretty low.

Some of us need to run higher octane in our designed-for-87-octane BMWs because of cylinder deposits, etc., which effectively increase compression and bring on pre-detonation (knocking) under load.

Does your car seem to run rich? Pull the plugs and have a look-see. All kinds of useful info in the archives about running rich - fuel system and ignition system are both areas to check out.

I was using my OBC to get the Average Gas Mileage and it seemed pathetically low, everyone always says they get about 20mpg.....but my average says only 14.7mpg....and thats after I added some STP Fuel Injector Cleaner, it went up .3mpg...not too impressive, but that was an almost instant jump. I do mess around in the car (I.E. the occasional 120mph splurge and the occasional show the punk in the Camero up at the stop light), and I mostly do stop and go driving, but it should be around 15.5-17mpg atleast...Any one have any ideas if there is a problem with the car;s fuel system or engine preformance...she's got 168k on her..., or is it just b/c I mess around in it.

PS anyone know of any squeaking noise from the front of the engine, its a loud squeal type but its constant, not sporadic like under acceleration, I suspect the fan belt (or the fan itself), my dad thinks its the timing chain...any ideas on this one too

Greetings from Toronto...
As far as your gas-mileage question, well I was getting pretty poor mileage using 89 octane up here in Canada. The higher the mileage, the more your timing-chain is likely to be stretched out if you haven't had it replaced (pricey repair job and unnecessary unless your car is cranking alot on startup) and therefore your firing or timing will be a bit retarded --- this long-winded explanation is to suggest that your car may want the higher-octane variety. You might find if you put in 92 octane or more, your gas-mileage will improve. And, if you're doing the odd 120 mph run in your cruiser, well your car will definitely want the higher octane. I've got 358,000 KM's on my 85 735i and the timing is retarded - car likes the higher octane. I get better mileage with 92 or 94 octane.

As for your squeeling noise in the front. I had a similar problem. The noise would occur at lower rpm's usually and was temperature sensitive. The fan clutch is your likely suspect. Clutch is designed to contract or allow for slower fan speed at colder temperatures and then expand and "grip" when you increase engine rpm's (centrifugal force pushes clutch out to grip). Problem is, through this process of the clutch contracting and expanding you're getting metal on metal contact. All I did was spray lithium grease and chain oil through the small "breather" holes of the housing to the clutch and problem solved. Carefull not to grease up the fan-belt as you do this.

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