One of the most consistent failures in the BMW Z3 is the gas gauge. I’ve heard different excuses as to why the gas gauge fails, but rather than pretend to be an engineer or parts inspector let me just share with you some observations I have made regarding my wacky gas gauge.
Let me start by saying I never had a problem during my first year of ownership. But others were having problems during that time so I heard a lot of speculation regarding what caused the failure and I got to see what BMW’s fix was for those under warranty. I can almost pin-point the exact time mine started acting up. I was refueling and for some reason, when the gas pumped stopped I squeezed the pump trigger one more time. I don’t know why I did it, I had been warned not to yet for some reason I did it.
It was long afterwards I saw the gas gauge do its first flip-flop dance between empty and full. The error was initially intermittent, but over time it has become very consistent. Now mine always (and I do mean always) does its dance between empty and full right after I refuel. This will continue until I travel roughly 30 miles, I’ve never noticed the problem beyond the first 30 miles of a tank. Couple months ago I decided to try an experiment, instead of refilling until the pump clicks off I started buying my gas in $10 increments (never filling the tank all the way). The gas gauge never did its dance during the 4 or 5 tanks that I did the $10 thing. So at least in my case, these observations seem to back up the theory that the failure is related to the sending unit. I’ve learned to live with it, but learn from my experiences and resist the urge to squeeze that gas pump trigger again once it clicks off.
I have made the decision to live with it rather than have it fixed because I am not comfortable with the “fix”. To get to the sending unit BMW has to cut the carpet behind the passenger seat. Then they have to hook a hose and drain the gas tank (hopefully without leaving your interior smelling like gasoline). If you look behind the right hand seat you can see a seam in the carpet, this is where they will make the cut. Once the sending unit is replaced the carpet is glued back down. Sounds simple enough but I have seen more than one Z3 after this fix where the carpet flap has come unglued and ends up looking like a bad toupee. It also appears the new sending units are not necessarily any more reliable than the original ones.
I’ve owned my M roadster over four years now and my refueling habits are fairly consistent. I’ll usually refuel before the low fuel light comes on, if I push it and the low fuel light comes on then pull off at the next available gas station. I use my trip odometer to measure distance on a tankful, and on average it usually says around 240 miles since my last refueling and it will take around 12 gallons to fill the tank back up.
One day after work I pushed it a too far, the engine sputtered then quit. I zig-zagged a little and got another second or two of runtime before it quit for good. Luckily I was going downhill at the time so I managed to coast into the gas station and right up to the pump. I got lucky, and this provided me with an opportunity. I now know it takes 13.3 gallons to fill a completely empty tank. I started taking notes after that and refilling at different points on my gas gauge. It takes 8.9 gallons to fill a tank that my gauge indicates is half empty. 12.3 gallons to fill a tank right after the low fuel light comes on. I will continue to take measurements at various points on my fuel gauge and update this page.
One last final note: Remember that my fuel gauge has problems so my measurements may not be typical of most Z3s.