just out of curiousity...fuel guage question [Archive] - GrandAmGT.com Forum

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scs411scs
07-23-2006, 10:32 PM
not really a problem, more of an oddity really...i was browsing through fuel mileage posts and found out that im pretty well in the average it seems at about 280(city)-300(highway) miles per tank, but an odd thing that i was just curious about is the rate that the guage goes down. for example on a recent driving trip i left with a full tank, went 200 miles and the needle was straight up half-tank...youd think id be able to go 400 miles on the tank then, right? nope, 260 was 1/4 full and at 280 the fuel light came on....so why does the second "half" of the tank go so much more quickly? or is the halfway mark on the guage not a half tank at all? youd think if anything went more quickly it would be the first half having to carry the extra fuel weight around (having also flown planes, i know the difference that fuel alone can make in weight, haha)

anyway, just a what for, and wondering if anyone else has experienced this too...

badboy2451
07-23-2006, 10:42 PM
i have the same problem, thats just the way it works from what i understand...unless you have some crazy gauge readings which would require a new sending unit but yours sounds normal

Don Punani
07-24-2006, 12:18 AM
This has been a GM problem for many years. Almost every GM vehicle I've owned tended to stay on or near Full for quite a while. Once the gauge got to half, it would drop quickly and it took almost no time to go from a quarter to Empty. Just one of those things. Apparently not many folks seem to mind, since GM hasn't really bothered to address/fix the problem

eaglesrealm
07-24-2006, 08:33 PM
This has been a GM problem for many years. Almost every GM vehicle I've owned tended to stay on or near Full for quite a while. Once the gauge got to half, it would drop quickly and it took almost no time to go from a quarter to Empty. Just one of those things. Apparently not many folks seem to mind, since GM hasn't really bothered to address/fix the problem


It's not really a GM problem, it's just how a traditional system works. There is a float in your tank, much like in your toilet bowl. When you fill it, the float goes up and tells your sending unit to tell the gauge you are full. What happens is, the float sits on TOP of the fuel. So you are filling and it goes up, then maxes out. However, at the top of it's stroke, it is sitting on top of the fuel at this point and hitting the top of the tank at the same time. You are not full at this point, you continue to fill until the gas hits the top of the tank and shuts off the pump.
So then you burn fuel, but the float will stick at the top until the gas is down enough that the top of the fuel is back at the bottom of the float. Then it should go down at a fairly linear rate until you get to the bottom and the opposite will happen. You will get to empty when the float hits the bottom, but you will have extra fuel left. In the simplest sense, if the float is 1" in diameter, the float will bottom out and you will have 1" depth of fuel left before you are really out.

Hope that made sense. Sorry for the ramble.

Don Punani
07-24-2006, 08:48 PM
Your explanation makes sense and I'm not trying to bash GM...in my personal experience and many, many people that I know is that I've found that GM fuel gauges are far from "linear" in their readings. There is a large disparity in how fast the gauge goes from a little under half to empty when compared to how fast it travels from full to a little under a half. Yes, most gauges will linger at full for awhile for the exact reasons cited above. GMs in particular seem to drop to E quickly once you get a ways under half a tank. On the other hand, once you "get used to" how the gauge travels, you tend to develop a sense of how far you can really go no matter where the gauge reads. It's like a right of passage;) I think this is the sixth GM car I've owned and they all had the same trait. I also had an '84 Civic and unfortunately lost my '03 Acura CL and their gauges were both pretty much dead on. Don't get me wrong, I like GM vehicles, but this is definitely a trademark of theirs.

slowbird
07-25-2006, 06:49 AM
Yea...all my GM vehicles had this issue.