318is Fuel Mileage Problem

[AndrewBird]

The only valid method of obtaining fuel mileage is to record the mileage (or zero the trip meter), fill the tank, drive the car until it needs fuel, note the amount of fuel needed to fill the tank, and divide the that by the miles driven. You will get better numbers by recording starting mileage with a full tank, recording fuel added for each of several refills, compute the total fuel usage and divide by total mileage.

This.

Unless you rant he car completely out of gas, dividing the mileage by the tank capacity will not give you an accurate reading. You need to determine actual fuel usage, taking into account for any fuel left in the tank. Fill your tank, reset the trip meter, then when you fill up again, take the mileage and divide it by the number of gallons it took to fill the car again.

[NickMav]

If you check the IPB (realoem.com or similar) I believe you will find that all US 318 cars had a 55L tank. All 325 cars had the same tank up to 8/87, when the tank was changed to a 63L type. The easy way to tell difference is that the 55L tank has a single opening on the right side for the pump/sensor and the 63L tank has an opening on both sides. I believe that some non-US 318 cars had tank smaller than 55L.

The only valid method of obtaining fuel mileage is to record the mileage (or zero the trip meter), fill the tank, drive the car until it needs fuel, note the amount of fuel needed to fill the tank, and divide the that by the miles driven. You will get better numbers by recording starting mileage with a full tank, recording fuel added for each of several refills, compute the total fuel usage and divide by total mileage.

Checked realoem with my vin. Says I have the 55L tank. Under my back seat though theres two openings? Weird

[AustinK425]

OK I have this problem as well! but 20mpg plus good site to keep track is fuelly.com

[NickMav]

alright so took out my seat i have the two openings. took out the one on the right expecting to see a sending unit thinking i have the 63l tank and theres nothing there? guess i have the 55l one but i still dont see how im filling up more than that at the gas station.



got the second one off and find the fuel pump and everything. took off the one connecter that plugs into the pump and measured resistance got .03 18 and 78 ohms. dont know what its suppose to be but think my sending unit needs to be replaced anyway since my fuel gauage always reads half a tank as empty. Changed my sparkplugs and ordered new 02 and sending unit as well as pipe that connects both sides on tank. lets see how this plays out will update evetually

[AustinK425]

In for an answer. I think mine is most likely my tack but a bit unsure.

[AustinK425]

Any updates? my idle holds at 400 but i cant tell if that from my dinan chip or that its in need of a solid overhaul.

[NickMav]

Any updates? my idle holds at 400 but i cant tell if that from my dinan chip or that its in need of a solid overhaul.

400 sounds low, mine idles at 800 all the time. i put a full tank and im rechecking how my miles i can go right now im around 170 and a little over 1/2 tank. The sending unit fixed my issue with the gauge. I didnt order the 02 yet but if my gas milage comes up poor again i guess ill be checking that out

[decay]

alright so took out my seat i have the two openings. took out the one on the right expecting to see a sending unit thinking i have the 63l tank and theres nothing there? guess i have the 55l one but i still dont see how im filling up more than that at the gas station.

i put some pics of the 2 tanks in another thread in the M42 forum recently- looking at yours from underneath may be a better way to determine which you have.