While I'm thinking about it.. I summon your mechanical minds...

[HWKII]

So, my car, 1992 E30 318i. Has a 1.8L M42 engine in it that's supposed to get about 28-30mpg. I'm getting <20mpg (close, but around there) which might partially be down to me learning to drive, but not much. In spite of my paying more attention to that little MPG needle on the dash, and shifting up when cruising, I've never gotten more than 20mpg. That's worse than my buddy's 325 by a long while.

Where do I need to start on the MPG side of things? Spark plugs, air filters, what else? The engine is peppy so long as I keep the revs above 3,500 on anything that resembles a hill (having to floor it to avoid losing speed is not doing me any favors on those hills, being passed by minivans is mildly embarrassing). 

Do I need to change my driving style and get higher in the revs before shifting up to cruise? 

Help.

[RackAttack]

Definitely check the spark plugs and air filter, as well as the ignition coils and MAF sensor.

Spark plugs would be first on my list, especially if you don't know how long it's been since they've been changed.

[vkaifh]

my mpg goes down dramatically when driving only short distances (less than 10 miles) or of course in the city with lots of stop and go. So how do you use the car?

The manufacturer's mpg numbers are unreachable anyway, those were determined under perfect conditions in a lab with tires filled up until they almost explode. They are maybe valuable to compare different cars but are worthless as an expectation of what you will spend at the gas station.

[timneyb]

What VK said.

Hills, short distances, speed and cold kills. Until you normalise for that it's hard to know how much, if any, of the problem is mechanical. Also, make sure to do your calculations based on the odometer and how much gas you actually put in the tank. The accuracy of that little needle is questionable, and good mostly for relative values once you have an empirical calibration.

My (nearly brand new) Impretzel makes nowhere near the stated numbers unless I've got long stretches of level ground with only a few lights (for the city values) and have time for the engine to get really warm.

[clacksman]

Also, make sure to do your calculations based on the odometer and how much gas you actually put in the tank. The accuracy of that little needle is questionable, and good mostly for relative values once you have an empirical calibration.

This too. I think the needle is just a vacuum gauge, which is good to help adjust the loose nut behind the wheel but approximately useless for actual numbers.

Add fuel filter to the list of things to check age of, and run some fuel system cleaner through it - gas left in the car longer than about 3 months will leave a sort of varnish on everything it touches.

Does the internet forumite scum get 30MPG out of those? I averaged 27-28MPG (consuming less than 10 litres per 100km via measuring both) in the old wagon which exactly nobody believes - just kept it running properly, and no weird hypermile driving other than avoiding idling and driving smooooooooothly. Synthetic goo in all of the things will help, premium fuel may help a bit (helped me a bit, but probably not enough to work out to being cheaper).

[Wallhugger60]

Tire pressures plus what everyone else said. Is it fuel injected or throttle body? I don't think it's old enough for a carb. Lotsa little things will certainly add up. That fuel gunk will clean some of the crud out, but if the nozzles aren't atomizing the fuel and it's dumpin it in that will hurt economy too. The car is twenty+ and if you don't know the maint. done over the years it's a lot of inspect and replace in your future assuming you're that anal about the mileage   

Tracy

[HWKII]

Sooo much wisdom to reply to:


Rack: Thanks, glad I was not totally off base.


VK: Since I'm still learning to drive, I'm mostly doing it in marathon sessions of 2-4 hours at a time. Most of it is country road 45mph in 4th kind of cruising, but also highways. THIS is a pretty typical Sunday afternoon for me. Or something approximating it. Blue line up and grey line (HWY 18) going back home.


Timney: I'm not actually so much worried about what the needle says (other than as to remind me that I might be driving like a nutcase); this is based on comparing distance travelled on the odometer to the amount of gallons that go in the tank when I fill up. Last fill up was 10.6 gallons and I got 201 miles out of it. 18.9mpg.


clacksman: Internet scum claim anything from 25-35mpg, some scum even say closer to 40 but I suspect 40 is cruising in the right hand lane at 55 in 5th. Speed limit being 70 on highways here in Washington makes that somewhat impractical. BMW says over 30, the restoration guide I bought on the car suggest 28 (to augment the Bentley manual, since it points out more of the common faults).


Wall: Wiki says this about the engine in my car, "The M42B18 has a displacement of 1,796 cc, which is achieved through a bore of 84 mm and a stroke of 81 mm.^[6] The engine uses Bosch Motronic 1.7 fuel injection." I'm the 3rd owner of the car, the 2nd owner bought it from a guy who, I'm pretty sure, drove it until he didn't want it any more and it sat around. 2nd owner replaced the radio, struts/shocks, put in some slammin' spings yo, and replaced the roof. The poor engine has, to my knowledge, not gotten much love.




I'm taking the car down to Portland in the morning and I'm getting new OEM springs, new control arms and bushings, and rear brakes fitted. The guy I'm taking it to is a long time friend of a guy I've worked with for a couple of years now who shares a love of all things E30. Mike calls him the E30 Whisperer, so I'll pick his brain tons tomorrow for sure. I intend to spend as much time under the car with him as he'll let me. I went in to it knowing that it would need a little work but it's very driveable as is. Just a bit more gas hungry than I'd have guessed.

[Wallhugger60]

Well sounds like yer pretty realistic with expectations and most important....not afraid of dirt  

[clacksman]

Well sounds like yer pretty realistic with expectations and most important....not afraid of dirt  

Second.

[HWKII]

Down to Portland at between 70-80mph from Seattle, combined with a short back country jaunt before I left and managed to get 26mpg without changing a thing. Still going to do spark plugs and filters just because I have no idea when they were last touched.

Ride height restored to stock (thank god...), new control arms and bushings, new rear brakes. Brake pedal is a lot softer than I recall it being but it stops nicely. Not as violent as it was before (old pedal felt like a switch). Jason gave me some tips on what is going to be coming in the car's near future: Clutch replacement owing to stiff pedal/lubricant worn off throttle bearing, maybe profile gasket since this is one of those things that this engine deals with a lot. A couple hoses that are looking a bit ragged including the hose coming off the air filter/vacuum sensor.

Consensus was it was a good buy and a great value - not a spot of rust or rot anywhere on the car as well, which I was keen to go hunting for while it was up on the lifts.

[clacksman]

Jason gave me some tips on what is going to be coming in the car's near future: Clutch replacement owing to stiff pedal/lubricant worn off throttle bearing, maybe profile gasket since this is one of those things that this engine deals with a lot. A couple hoses that are looking a bit ragged including the hose coming off the air filter/vacuum sensor.

'Throwout bearing' not 'throttle bearing'?

Googled 'profile gasket', that looks like a fun one.

[HWKII]

Jason gave me some tips on what is going to be coming in the car's near future: Clutch replacement owing to stiff pedal/lubricant worn off throttle bearing, maybe profile gasket since this is one of those things that this engine deals with a lot. A couple hoses that are looking a bit ragged including the hose coming off the air filter/vacuum sensor.

'Throwout bearing' not 'throttle bearing'?

Googled 'profile gasket', that looks like a fun one.

Yes, throwout bearing, misheard him. Just looked it up.

Yeeeeeeeeah... requires pulling the head. Could be a fun project, but not just now...

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