fuel mileage
- Thread starter jimhorton1963
- Start date
Huh??? Maybe you need this advice too! 23mpg highway is what I get in my e34 535i on the highway with a 3.91 rear end (stock was 3.46) - and the M30 is a total gas hog.
Anyways,
I was getting roughly 29 - 31 mpg doing a steady 70 - 75 mph back and forth from here (lancaster) to williamsport - so its hilly too. That was in my 1988 325is, that had 182k miles the day it was totaled.
Before I did all of this I would get about 25 mpg.
Here's what I did that GREATLY improved my gas mileage (it pretty much needs a tune up)
-Spark Plugs
-Plug wires
-Distributor cap and rotor
-Fuel filter
-Oxygen sensor (this made a big difference in my car)
-Thermostat
-Engine temperature sensor (For the ECU, not the temperature sensor for the gauges...)
-Air filter
-Fuel pressure regulator (check that the small vacuume line for this isn't broken, mine was all cracked)
-Charcoal emissions canister (if it's bad, there will be liquid fuel evaporating from the canister instead of just fumes - the liquid is supposed to return to the gas tank)
-Fan clutch (I didn't do this - but if your fan clutch is bad and spins ALL the time, it's going to put a big drag on the motor, especially on the highway.)
Things to check:
-Check for ANY VACUUME LEAKS. These will greatly reduce gas mileage. Check or even change all the boots and vacuume hoses. Cracked hoses will 90% of the time leak.
-Make sure the air flow meter and throttle body are CLEAN and move freely. Make sure your idle control valve works (or at least fits in the boot properly)
-Valve adjustment and new valve cover gasket - possibly new oil cap (prevent vacuume leaks). The valve adjustment will be a HUGE thing. I would set the valves just a little bit tighter than factory spec. They will be a little quieter, and you figure your cam's are a little smaller than they were 17 years ago... bently lists 0.30mm (0.012in) with the engine hot, or 0.25mm (0.010in) with the engine cold. I did the adjustment with a warm engine to 0.25mm. Then I drove it, got it heated back up, and went back in to re-readjust it to make sure they were all 0.25mm. People warn about the valves being burnt up if adjusted to tight, but this isn't a huge difference, and like I said the parts of the car aren't all in spec anymore (ie the cam, rockers, etc.)
-Run some decent fuel injector cleaner through (IE Seafoam right before you change the oil, and maybe some redline fuel system cleaner)
-Check tire pressure. Fill them up near the higher end of the allowed fill pressure. Drive it on the highway then if you want, just let some air out again if you do a lot of back-road driving![[;)]](/images/smilies/wink.png "Wink [;)]")
-Make sure the brakes aren't sticking at all, and that the e-brake is adjusted properly.
-Drive with windows closed, AC on. That will get you better gas mileage on the highway (not the city though)
It all sounds like a lot but it is fairly easy maintainence and total cost won't be more than $250 if you know where and what to buy - plus it's stuff that will generally make the car run better, so you can justify the purchases. I could be wrong but i'm pretty damn sure that I got better gas mileage at 70-75 than anything else. I'm basing all of this on filling the tank, NOT the obc - but the obc was pretty much spot on. When I would go 80mph I'd see a 2mpg decrease, when going 65mph it was about 1mpg less than the 70-75 gas mileage.
Anyways,
I was getting roughly 29 - 31 mpg doing a steady 70 - 75 mph back and forth from here (lancaster) to williamsport - so its hilly too. That was in my 1988 325is, that had 182k miles the day it was totaled.
Before I did all of this I would get about 25 mpg.
Here's what I did that GREATLY improved my gas mileage (it pretty much needs a tune up)
-Spark Plugs
-Plug wires
-Distributor cap and rotor
-Fuel filter
-Oxygen sensor (this made a big difference in my car)
-Thermostat
-Engine temperature sensor (For the ECU, not the temperature sensor for the gauges...)
-Air filter
-Fuel pressure regulator (check that the small vacuume line for this isn't broken, mine was all cracked)
-Charcoal emissions canister (if it's bad, there will be liquid fuel evaporating from the canister instead of just fumes - the liquid is supposed to return to the gas tank)
-Fan clutch (I didn't do this - but if your fan clutch is bad and spins ALL the time, it's going to put a big drag on the motor, especially on the highway.)
Things to check:
-Check for ANY VACUUME LEAKS. These will greatly reduce gas mileage. Check or even change all the boots and vacuume hoses. Cracked hoses will 90% of the time leak.
-Make sure the air flow meter and throttle body are CLEAN and move freely. Make sure your idle control valve works (or at least fits in the boot properly)
-Valve adjustment and new valve cover gasket - possibly new oil cap (prevent vacuume leaks). The valve adjustment will be a HUGE thing. I would set the valves just a little bit tighter than factory spec. They will be a little quieter, and you figure your cam's are a little smaller than they were 17 years ago... bently lists 0.30mm (0.012in) with the engine hot, or 0.25mm (0.010in) with the engine cold. I did the adjustment with a warm engine to 0.25mm. Then I drove it, got it heated back up, and went back in to re-readjust it to make sure they were all 0.25mm. People warn about the valves being burnt up if adjusted to tight, but this isn't a huge difference, and like I said the parts of the car aren't all in spec anymore (ie the cam, rockers, etc.)
-Run some decent fuel injector cleaner through (IE Seafoam right before you change the oil, and maybe some redline fuel system cleaner)
-Check tire pressure. Fill them up near the higher end of the allowed fill pressure. Drive it on the highway then if you want, just let some air out again if you do a lot of back-road driving
-Make sure the brakes aren't sticking at all, and that the e-brake is adjusted properly.
-Drive with windows closed, AC on. That will get you better gas mileage on the highway (not the city though)
It all sounds like a lot but it is fairly easy maintainence and total cost won't be more than $250 if you know where and what to buy - plus it's stuff that will generally make the car run better, so you can justify the purchases. I could be wrong but i'm pretty damn sure that I got better gas mileage at 70-75 than anything else. I'm basing all of this on filling the tank, NOT the obc - but the obc was pretty much spot on. When I would go 80mph I'd see a 2mpg decrease, when going 65mph it was about 1mpg less than the 70-75 gas mileage.
well, it looks as though i do have a higher mark to shoot for. i make a trip from michigan to texas and back every6 weeks. with the price of fuel going up i wanted to know if i was getting the best out of the car that i could. i know that if i drive at a slower speed i will get better mileage but i have to make the trip in one day each way. i do take care of the car as well as i can, and repair what i can before buying any parts from the dealer. on my last trip it died the evening before i left. along the highway i found that the fuel transfer pump was not running. we towed the car back to my brothers and removed the pump from the tank. no replacement was available in dallas on a saturday night. i carefully cut the pump open and replaced the brushes (which i carved from a set removed from a dewalt screw gun ) , and repaired the burned plastic with j b weld. i j b welded the plastic case back together and it worked. i instaled the pump back into the tank and found that the high presure pump was not working either. i removed the top of the pump from the aluminum body of the pump, and replaced the brushes in this pump as well. a bit of j b weld around the seal and reinstalling the head into the aluminum pump body sealed it up nicely. i was suprised that the insides of theese motors were made in a way that if you could get inside they were serviceable. i made the trip home without incident or fuel leak. i love this little car.
![[rofl]](/images/smilies/icon_smile_rofl.gif "ROFL [rofl]"){kind=icon}
if only I could retain that kind of knowledge about important things!! Like I said before, it's kind of sad why I know all of this... becuase I obsessed with having my e30 run perfect.