318is Fuel Mileage Problem

[eur04lif3]

I just checked realoem and put in my vin and it said i have a 55 liter tank or a 14.5 gallon tank. Im confused on what i have no im pretty sure the p.o didnt change the tank but my fuel gauge does read as f is full and 1/2 would be empty. I think its the sending unit that is causing that. I probably have the 14.5 gallon tank but thats still only like 17mpg

Wait, how are you getting your MPGs?

You should be doing the old-school way, every fill up check mileage and gallons filled up.

[eur04lif3]

Mitchell1 Says its 16.4 gallons or 62.1 liters. I was going to use the ngk spark plugs anyway. With new thermostat it is running right at the halfway mark before it would never even go past the quarter mark so i fixed that. Im going to change the 02 when I do the spark plugs and see what happens. Thier may be a vac leak to because under the intake where that mess is the p.o tapped up some hoses.

Ya, that's most likely your issue.

I get between 28-31, depending on whether i just cruise or sprint through corners. :up:
Worst i ever got was 27.8 and that was mostly city and old sparks and O2 sensor.

[NickMav]

I just checked realoem and put in my vin and it said i have a 55 liter tank or a 14.5 gallon tank. Im confused on what i have no im pretty sure the p.o didnt change the tank but my fuel gauge does read as f is full and 1/2 would be empty. I think its the sending unit that is causing that. I probably have the 14.5 gallon tank but thats still only like 17mpg

[NickMav]

Mitchell1 Says its 16.4 gallons or 62.1 liters. I was going to use the ngk spark plugs anyway. With new thermostat it is running right at the halfway mark before it would never even go past the quarter mark so i fixed that. Im going to change the 02 when I do the spark plugs and see what happens. Thier may be a vac leak to because under the intake where that mess is the p.o tapped up some hoses.

[gearheadE30]

Stock tank on 318is's is 12.6 gallons. 14.5 was for some of the 6-cylinder cars. I typically get between 28 and 32 mpg.

[e30Chris]

Get the plugs changed (avoid Bosch Platinum at all costs, NGK worked great for me) and change O2 sensor. Is it getting up to operating temp with the new thermostat? How's it idle and accelerate? Could be a vac leak too. And did you swap in a 16 gallon tank? The stock tank is 14.5.

[Dj Buttchug]

change o2 and check for vac leaks. I can get well over 400 miles to the tank on the freeway, also the tank is 12.6 gallons pretty sure

[NickMav]

Hello, I have a 91 318is M42 with 146,500 miles a supersprint catback exhaust and a 3.73 lsd. I averaged my mpg to around 16ish mpg. This should be way higher shouldnt it? Im going around 260 miles on a 16 gallon tank. I dont even really beat on it, I daily it to school and work. Im always shifting under 3k too and occasionally ill get on it to pass someone sometimes. Its not like im bounching off rev limiter and dumping the clutch either ill just take it up to around 6k no more. My car even smells rich sometimes so I know its getting to much fuel. I recently replaced the fuel filter, thermostat and coolant flush. Air filter is clean. Didnt have a chance to pull the plugs but was going to do that soon and most likely change 02s. Any ideas that I could be missing on why my mpg is so poor? Thanks guys