Just out of curiosity dose your gas gauge do this. When I drive the car my gauge seems to fluctuate a lot. When I start it it seems to drop half a tick to a full tick right away or with in a couple of minutes. As I drive it the gauge slowly comes back up. Every time I start it it dose the same thing, the gauge is always lower then when I turned it off. It seems even more pronounced at the last quarter of a tank. Anyone else get this?

Yes. I get excited by noticing how many miles per tank I have then the excitement is shattered when it drops two or three ticks in a couple seconds.

Just out of curiosity dose your gas gauge do this. When I drive the car my gauge seems to fluctuate a lot. When I start it it seems to drop half a tick to a full tick right away or with in a couple of minutes. As I drive it the gauge slowly comes back up. Every time I start it it dose the same thing, the gauge is always lower then when I turned it off. It seems even more pronounced at the last quarter of a tank. Anyone else get this?


I don't think that is normal. Sounds like your sending unit, probably located in the fuel tank, is acting up.

I think everyones probably does this. The system is updated constantly and is always calculating the position the gas gauge should be at according to how your currently driving, i.e. speed, throttle psoistion, etc... I would think its normal. Correct me if Im wrong though.

Seeing that the RX has a saddle tank, which straddles the drive shaft there must be a pump that moves fuel from one side to the other. This could explain the wired movement. This is just speculation, anyone no the facts of this?

YEA that's normal, quite takin them corners fast. With all that gas sloshin around, it gets confused.

Doesnt seem normal to me. Mine does not behave that way. The sweeping action is very steady (and fast!) as gasoline is being sucked outta the tank.

I am not 100% sure about the RX-8 tank configuration but I work for a Fuel Pump and Module Manufacturer and know of this same problem for other similar designs (saddle tank) were the gauge has "funny" readings. There is a venturi that transfers the gas from the "minor" side of the saddle tank to the side where the fuel pump is located. When the engine is tured off, some of the gas from the fuel pump side of the saddle tank flows back to the side without the fuel pump. This gas transfer (when the engine is off) causes incorrect fuel level reading for a short time when the engine is restarted. Our customer has installed a check valve in it's newer products to prevent this problem from happening. We don't make the fuel pump and module assembly for the RX-8 so I don't know the specifics of their system.

I stand corrected...but it is kinda alarming how quickly the gas gauge needle goes from "full" to "3/4"! For me it's about 20-25 miles.

Yes. I get excited by noticing how many miles per tank I have then the excitement is shattered when it drops two or three ticks in a couple seconds.
I'd laugh if I weren't crying.

You have no idea how often this happens to me.
"HOLY CRAP! I've driven 100 miles and it's at where I normally drive only 70 miles! This tank is gonna kick ass!"

two minutes later, the needle has dropped 2 ticks.

"Damn."

It happens the other way to me sometimes though. Like according to the gas gauge I've driven like 20 miles less than I normally do at that point, but give it a day or so and I'm back to normal. The gas gauge is not to be trusted. :)

For me, usually I go to quarter at 50-60. To half at 110-120. To 3/4 at around 200. To light going on at 230.

Could be worse.. yanno if your low gas warning light didnt work properly at all.
I notice this happening every so often but as you and others stated its just the gauge adjusting itself. I had a Chevy W/T before this and that thing was yeah horrible, I never knew how much I had in the tank because a friend speculated that the floater or whateva was most likely messed up royaly. I'd fill the tank up, all 27 gallons of it and it would either be at Full or be about 1/8 the way past Full. I'd say keep a eye on it and if it annoys the hell out of you take it to Mazda and ask them to take a look at it.

It happens to me also, which is weird because I will be at just above 1/4 take for 40 miles

It happens to me also, which is weird because I will be at just above 1/4 take for 40 miles
yeah i'm with ya, mine enjoys staying at a 1/4 tank for awhile

Yeah Its The Fuel Moving From One Side To The Other

^ +1

I'd laugh if I weren't crying.

You have no idea how often this happens to me.
"HOLY CRAP! I've driven 100 miles and it's at where I normally drive only 70 miles! This tank is gonna kick ass!"

two minutes later, the needle has dropped 2 ticks.

"Damn."

It happens the other way to me sometimes though. Like according to the gas gauge I've driven like 20 miles less than I normally do at that point, but give it a day or so and I'm back to normal. The gas gauge is not to be trusted. :)

For me, usually I go to quarter at 50-60. To half at 110-120. To 3/4 at around 200. To light going on at 230.

lol! youve just described the exact emotional rollercoaster i ride with every tank of gas i drive on in my rx-8, including mileage umm milestones.

to the poster: i dont think ive noticed anything as drastic as what your describing, just an overall "the needle isnt consistent" sort of thing.

my moves around a fair bit, but it's almost always a consistent 70 miles per quarter... and another 50 or so below E...

I noticed slight fluctionations, but nothing to cause me concern.

The Chrysler mini-vans stay pegged a FULL for quite a while, then drop like a rock. I swear I've seen my wife's van reading nearly full with nearly 100 miles on the tank (it typically has a 360-mile range so that math doesn't work).

My F150 had dual tanks. One tank would read full forever and not move. The other worked the opposite: dropped from full to empty after just a few miles on that side.

Frankly, there's less variation in the gauge than I would expect from all my turning, accelerating, stopping and all the rolling hills in the area.

Well at least I'm not going crazy, glad to hear your all in the same boat. I also have felt the crushing pain of what appears to be great mileage disappearing in the final 1/4 thankful. Its like having a good looking girl slowly unbutton her sweater only to find out she is wearing a tee shirt ;-)

Mine seems broken, it drops to the bottom like a rock :)

For me, usually I go to quarter at 50-60. To half at 110-120. To 3/4 at around 200. To light going on at 230.

I WISH... I get ~200mi off a gas tank, so it's 50mi at each major tick 'cept for the last 1/4 tank of gas is hillarious. I'm at like, 200 with just under a 1/4 left, then at 210 I'm on the light and at 220 (if I'm lucky) I'm below the red final tick.... it's hillarious how OFF it is on that last 1/4 tank.

Also, fuel expands a lot with heat. That will make the float change. Try putting gas in a red plastic gas can and set it in the sun. It will expand a lot. So driving, the exhaust will heat up the tank and the gas will expand.

Mike

I mainly notice that the gauge doesn't go down consistently for the readings so much. It's not that far off but doesnt' drop consistently. Starting at full, my has around 80 at the first 1/4 down mark. It has around 150-160 at the half, the next quarter shows up anywhere between 220-250. My light will come on around 290ish.

Also, fuel expands a lot with heat. That will make the float change. Try putting gas in a red plastic gas can and set it in the sun. It will expand a lot. So driving, the exhaust will heat up the tank and the gas will expand.

Mike

Very good point, I forgot the exhaust pipe runs right next to the gas tank. This would explain why the gas gauge rises when driving in the car for a while and falls again after the car cools off.

So based on the feed back we now know the gas gauge is a little inaccurate and the heat from the exhaust further effects the accuracy by expanding the fuel during use which accounts for my gauge raising during use and falling considerably when the car is restarted the next morning or at the end of work. It would also explain why the readings fluctuate more when your down to a quarter of a tank, the gas expands even more because there is less of it absorbing the heat from the exhaust. Put the saddle tank into the equation and the mystery is solved.

Excellent, thanks for the input.

I WISH... I get ~200mi off a gas tank, so it's 50mi at each major tick 'cept for the last 1/4 tank of gas is hillarious. I'm at like, 200 with just under a 1/4 left, then at 210 I'm on the light and at 220 (if I'm lucky) I'm below the red final tick.... it's hillarious how OFF it is on that last 1/4 tank.

This is not good. If this happens to me tomorrow I may run out of gas before I make it to shell(5 or 6 miles away.) I have about 2 or 3 ticks left but no light. I'm at about 250 miles.(70% highway)

I am not 100% sure about the RX-8 tank configuration but I work for a Fuel Pump and Module Manufacturer and know of this same problem for other similar designs (saddle tank) were the gauge has "funny" readings. There is a venturi that transfers the gas from the "minor" side of the saddle tank to the side where the fuel pump is located. When the engine is tured off, some of the gas from the fuel pump side of the saddle tank flows back to the side without the fuel pump. This gas transfer (when the engine is off) causes incorrect fuel level reading for a short time when the engine is restarted. Our customer has installed a check valve in it's newer products to prevent this problem from happening. We don't make the fuel pump and module assembly for the RX-8 so I don't know the specifics of their system.

Hey j330i, ave you seen this thread? http://www.rx8club.com/showthread.php?t=89855

It sounds like someone with your background might be able to help out there.

...I'm at like, 200 with just under a 1/4 left, then at 210 I'm on the light and at 220 (if I'm lucky) I'm below the red final tick.... it's hillarious how OFF it is on that last 1/4 tank.

Same here. Yesterday I was a 200 with a 1/4 left; at 218 the light came on. WTF

This is not good. If this happens to me tomorrow I may run out of gas before I make it to shell(5 or 6 miles away.) I have about 2 or 3 ticks left but no light. I'm at about 250 miles.(70% highway)
When the light goes on you have about 2.5 gallons left in your tank. You should be plenty fine.

Maybe, but when I pulled into the garage I was very happy because I was behind a black 8 on the way home from work and it made me happy and I was revving her to like 9k several times.

Sorry to revive this thread but my gas gauge has just started acting crazy. (That or I am looking more closely at everything since getting my car back from the dealer.)
Tonight I turned on my car and the gas gauge showed one tick above 1/4. I waited for a couple of minutes to let the engine warm up and the gas gauge was 2 ticks below 1/4. I started watching the gauge and every several seconds it would change to somewhere between 1 tick above and 2 ticks below 1/4. Anyone else have this problem and/or should I be concerned?

I'm assuming your cars are parked on inclines. Same thing happened with my older car too.

Funny thing this morning, I'm taking a cloverleaf exit ramp at highway speeds and I see my fuel gauge go UP 2 ticks when I hit the bottom of the ramp.

There might have been a very slight incline ( < 1 degree). I could understand it changing from the incline to level ground. However I was stopped and in neutral the entire time.

Hmm, this thread makes me want to watch my tank more carefully. I don't think I have the same issue, but alas, I can't be 100% positive...*rigs up the camera to watch for me*

I don't know that it's so much to worry about just yet. You may want to keep an eye on it though.

I've arived at my destination with "more" gas than I started with.

When I start it it seems to drop half a tick to a full tick right away or with in a couple of minutes.

That is the fun indicator, telling you that you're driving your car properly. Just try not to have fun all the time.

I filled up yesterday with the needle 1-2 ticks below the half way point and I topped up with 28.5L (and it's supposed to be a 60L tank). So I dont pay much attention to the gauge

Yeah I get the fun indicator as well, your car is alright. Read back a few pages they talk about how it is how our tank is a saddle shape and its the fuel equalizing on both sides that cause the reading.

Its normal and its does, not dose :p

Its normal and its does, not dose :p

It's "it's" not "its" :-P

It's "it's" not "its" :-P

Haha using its rather than it's was me being lazy :)

This is normal for my car, the RX has a very screwy gas gauge and the closer you watch it the more you realize it plain erratic.

I believe this is caused by two issues, one is the fact that the RX uses a saddle tank which pumps gas from one side to the other which causes issues. The second problem is the exhaust pipe runs between the saddle tank and as it heats the gas the reading is thrown off. When the car is started the amount of gas in the tank appears less then when the tank was hot so you see a drop after a few minutes of operation as the gauge system adjusts. The weather also effects this as I see difference between operation in the winter and the summer. This of course is just my speculation but it does make sense.