is this possible ? what mileage should I expect ?

[fairchild]

OK---- I took the z-3 out on a little daytrip. Just got the valve cover gasket replaced. Much less oil smell and smoke clouds.

I just mapped my route and I drove round trip about 80 miles. before I left I topped off the fuel--- it took 6 gallons.
when I returned at the end of the day-- the gauge showed I had used about 1/4 of the 6 gallons. That comes to 1.5 gallons.
Now I remember that gas gauges are usually hinged at the bottom to the most error (dis-proportion) is at the top.
If I did 80 miles and even used 2 gallons-- thats still 40 mpg. I wouldnt think it would be any better than about 35 ....????

what mileage should I expect ? ( it is a 2000 year 2.5 liter with automatic trans)

Tim

[MIKYZZ4]

Don't calculate based on the fuel gauge, but on actual fuel used,
You should have topped off after your little day trip,
which would have indicated actual amount of fuel used,
thus:miles traveled = 80mi,
divided by
fuel consumed = gallons required for second top-off.

80 miles/xx.xx gallons=MPG

[khammack]

As MIKYZZ4 said, our fuel gauges are not at all accurate. Use his method to get your mileage. Also, don't put any additional gas into your car after the pump cuts off. If you do, you will start to get issues because our cars don't like it when you do that.

[328 Power 04]

When it gets to half, you've already used more than 2/3 of the tank.

[s8ilver]

When it gets to half, you've already used more than 2/3 of the tank.

Yep, and after you start the car after a fill up, it's technically not even full anymore. Just drive till the light comes on, fill up, and repeat.

[Vintage42]

... Just drive till the light comes on, fill up, and repeat.

I would not take it that low unless you know there is a station nearby. Why risk running the fuel pump dry? Why not fill up at least by 1/4?

[BUCK57]

Gas? We don't need no stinkin' gas!!! MPG, who cares. If you do buy a prius. Drive and smile .... oh, I need gas. I used to live in CO knowing where gas was up in dem dar hills Bounced over dis pass and dat pass to this pass ... oh my. I did this on my 01 K1200LT and did same in 98 M. So many gallons of gas to burn. I try to do my share!!!

[zellamay]

You can't even measure mileage based on one gas tank. It can be telling to see what you get on each tank, compared to how you drove, but it takes several tanks to really know what you're getting. I use the odometer with each tankful, calculate the mileage, then keep a running tab. On my 98 Z3M I get 18 if I use the gas pedal a lot, 21 if I take it easy, on about 1/2 hwy/city. I've never seen my best mileage because I'm not willing to cruise at 65 long enough to find out.

[LannVouivre]

Also, don't put any additional gas into your car after the pump cuts off. If you do, you will start to get issues because our cars don't like it when you do that.

Any car with EVAP emissions equipment risks damage to said components if you top off. Sigh, every time I'm at the pump and I have to listen to some idiot top off 600 times I just want to rip my hair out. It only says not to do that on the pump, sometimes in your fuel door, in your manual, everywhere, but people still do it all the time!

[328 Power 04]

I do it all the time in my diesels. Lol.

But the foaming usually takes up about half to a full gallon of space. But no evaporative emissions to worry about.

[s8ilver]

I would not take it that low unless you know there is a station nearby. Why risk running the fuel pump dry? Why not fill up at least by 1/4?

99% of the time, I'm within a gallon of a station. When I bought the Roadster we were storming thru Utah on the way back and the light came on. Saw a sign that said "70 miles to the next station, exit here for fuel." The exit took us about 20 miles away from the highway and I still had about a gallon remaining. So now I just fill up when the light comes on, knowing I probably have 40 miles to empty. We averaged 22mpg on the trip, so I guess the light comes on at around 2 gallons remaining. I don't sweat the small stuff.

[saneesh8]

I have the exact same car. 2000 2.3 auto. Averages 20 mpg in the city driving. Most of them are 40-45mph. No change with fuel type / ac on/off or type of driving. Low was 19 and high was 21.

The fuel gauge, if i remember correctly, it takes 80-100 miles to reach 3/4, then another 50 to reach 1/2 and then it goes down really fast. Not like other cars. I usually fill it up around 170-180 miles.

[MIKYZZ4]

topping off soaks the charcoal canister with fuel.
Running vehicle, with low fuel warning light illuminated, decreases life of fuel pump.
I have been guilty of these 2 violations myself, many times in the PAST...no longer.

[s8ilver]

topping off soaks the charcoal canister with fuel.
Running vehicle, with low fuel warning light illuminated, decreases life of fuel pump.
I have been guilty of these 2 violations myself, many times in the PAST...no longer.

I never top off, but I have a hard time believing the pump is degrading the moment the light comes on. If you cavitate the pump or run it dry, sure. Our tank geometry doesn't really seem like you'd kill a pump until nearly dry. Anyways, just broke 150k in the Coupe and I always run it till the light comes on.

[LannVouivre]

I don't usually fill up until the light is on, but I'm also never more than 4 miles away from a gas station with 93 octane anyway. Heck, I don't usually even get to the station until the pointer is almost to the very end of the gauge. I don't think I've ever put in more than 12.5 gal going from "jeez that was close" to "full". I don't really think it's likely, at least on these newer cars, that you'd burn up a fuel pump unless you sat and cranked on empty...but, then again, I have never managed to damage a single pump for anything.

[rf900rkw]

I also run to the light, sometimes deep into the light. I have two preferred stations, one near the house, one near the shop. They are 25 miles apart. When the light comes on, I get fuel at the next preferred station. This could be 23 miles into the light, as it was this morning.

And I have put more than 13 gallons in these cars before. Once cruising down to Shuh Syndikat, I was just toodling along, not thinking about it much. When the fuel light finally came on, we were in stop-n-go on I77 in Mooresville 5pm Friday afternoon. I didn't want to get off into the gridlock of the surface streets, so figured I'd find a station once out of town. There turned out not to be any. We eventualy got to our exit for the hotel (has gas). I told Dianna that if we could make it up the uphill ramp we'll be okay; it's downhill the rest of the way to the hotel. That's when it dawned on her (she had been asleep) that I had just driven Va Beach to Charlotte, 365 miles, without stopping for fuel. She's one that fills at quarter tank... she freaked.

I see noting that is going to hurt the pump at low fuel levels as long as it' isn't sucking air. The argument that you will pick up the trash in the bottom only applies to cars that have floating pickups, which haven't been made in 80+ years. Any trash or water will be in the bottom. The pump pulls from the bottom, It doesn't matter if there is 13 gallons or a 1/4 gallon above it. If there is trash, the pump will find it.

[Watch Carefully]

The most I've put in is 11.7 gallons, but I've had mine only 13 months and 19 fill-ups. You can see my mileage average below--it's a mix of tanks spent ragging it out on the back roads and driving entirely on highways with a mind to stretch a tank.

Usually, I'm the guy who goes to the end of the tank, figuring I'm carrying less weight, so the mileage should be better at nearly empty than it is at full.
My wife is apparently Randy's long-lost cousin (She's one that fills at quarter tank)...but she's also a lead-foot. If you look at the chart of my daily driver (A4 Avant) fill-ups since 2014, there were three fill-ups when the wife drove my car exclusively (because I was overseas)...and they are by far the three lowest points on the graph!

[Randy Forbes]

Shape of the fuel tank may help you understand why the fuel gauge takes a long time to reach 1/2, then seems to plummet.

[328 Power 04]

BMW already applies a correction characteristic curve to the tank fill sensor data, to try to even it out, but the correction is obviously not enough.

Had I more project time, I would gather a ton of data from Fuelly, and recreate better characteristics curves, and reprogram the cluster's needle behavior to make up for the odd shaped tank.

- - - Updated - - -

Option 1: fix it

Option 2: accept it as a Z3 quirk

[Tallyho322]

I have a 6-cyl M, so my mileage will be different than yours, but I get between 20 and 25 mpg, depending on how I drive her. I can usually get ~300 miles on a tank, and that is what I pay attention to. Roughly 200 miles on first half, and 100 miles on the last 1/2 of the tank.

Fuel gauge is not very accurate as Randy pointed out...the tank is not symmetrical.

Left for work (115 miles RT) first few times when on 1/2 tank, just to have to stop at a toll road oasis to buy gas at a premium!

greg

[gmushial]

I also run to the light, sometimes deep into the light. I have two preferred stations, one near the house, one near the shop. They are 25 miles apart. When the light comes on, I get fuel at the next preferred station. This could be 23 miles into the light, as it was this morning.

<snip>

I see noting that is going to hurt the pump at low fuel levels as long as it' isn't sucking air. The argument that you will pick up the trash in the bottom only applies to cars that have floating pickups, which haven't been made in 80+ years. Any trash or water will be in the bottom. The pump pulls from the bottom, It doesn't matter if there is 13 gallons or a 1/4 gallon above it. If there is trash, the pump will find it.

What about the notion that the fuel is partially used to cool the pump, or the viscosity of the fuel keeps it from over-rev'ing, ie, trying to run it after it's empty is when the damage is done?

- - - Updated - - -

OK---- I took the z-3 out on a little daytrip. Just got the valve cover gasket replaced. Much less oil smell and smoke clouds.

I just mapped my route and I drove round trip about 80 miles. before I left I topped off the fuel--- it took 6 gallons.
when I returned at the end of the day-- the gauge showed I had used about 1/4 of the 6 gallons. That comes to 1.5 gallons.
Now I remember that gas gauges are usually hinged at the bottom to the most error (dis-proportion) is at the top.
If I did 80 miles and even used 2 gallons-- thats still 40 mpg. I wouldnt think it would be any better than about 35 ....????

what mileage should I expect ? ( it is a 2000 year 2.5 liter with automatic trans)

Tim

You might do a search, but there is at least one thread on what to expect... my '99 2.5L with 5MT, very very best is around 32 and change mpg (freeway); and on E15, tired plugs etc, more like 28mpg (again freeway). In town can be all over the place; or in bumper to bumper 1st gr, 2nd gr, back to 1st, stop, start again in 1st, stop, roll in 1st, stop, ie, 5pm I-10 LA, then can be as low as 12mpg.

[rf900rkw]

In our case, the returned fuel is not exposed to engine bay heat. If you consider the fuel line loop up to the drivers footwell and back to be the radiator, the pump has proper cooling even with less than 1/4 gallon left.

[gmushial]

In our case, the returned fuel is not exposed to engine bay heat. If you consider the fuel line loop up to the drivers footwell and back to be the radiator, the pump has proper cooling even with less than 1/4 gallon left.

I was thinking more in the case when the pump is run while dry - or what you're saying that the pump even dry has sufficient cooling? ... I know often in diesel pumps, the diesel oil is in fact used as a lube and a coolant; I can also think of various cryo pumps in spaceflight hardware - they rely on the -200deg material they're pumping to absorb the heat they generate from the mechanical pumping process to keep the bearings at a viable temp (ie, don't run them dry, or you get to replace a $400k pump)... I think this comes back from the Sirocco autox days, where one ran with as little fuel as possible, one of the very good shoes, one of my take aways was: you can run then out of fuel, and if you refill them before you try to run the fuel pump, no damage has been done; but if you try to crank it over and over trying to restart it, that's when the pump overheats and you're out a couple hundred $'s.

[Tallyho322]

I was thinking more in the case when the pump is run while dry....

i would think that if the pump ran dry, the engine would die and the pump would shut down. I see what you mean about cranking the engine trying to start it with an empty tank. But who would do that?


greg

[LannVouivre]

When the tank is run dry, the engine will not receive adequate fuel and shut off. The only reason the pump would keep running with nothing to pull would be if you continuously tried to crank the engine or bypassed the controlling circuits for the pump. Any time fuel is being pulled through the pump in large enough quantities to drive the engine, it shouldn't overheat. Most manufacturers try to anticipate the types that don't refill until they are close to being completely out, and design systems to function in those scenarios (frequently) without failing.