Low Fuel Lamp: How many gallons left when light goes on?

While the last of the fuel may warm up before the engine finally dies, a pump motor will never be uncovered...

Let us remember the various writeups on pump and sender repairs, and the fact that on normally aspirated cars the return fuel line dumps into the plastic cup. As long as the engine isn't consuming all the fuel sent forward, there is gonna' be fuel dropped back in the cup.

On the supercharged cars they went insane and tripled up, adding a shunt off the pump outlet itself, and then running THAT fuel through a venturi in the bottom of the cup to draw in even more fuel... These cups are never gonna go empty until the tank is dry and the car is flipped over!

I wonder what kind of RPM the N/A pumps run at, compared to the S/C pumps with the 2-speed module in the trunk... Are the N/A pumps noisier? Regardless, with all the engineering to keep the pump submerged and also to run it slow enough that I can't hear it after the prime-cycle, I don't really expect to need my spare pump-motor for a long, long time.

Interesting. I now have new found confidence in my 139,000 mile original pump. You are right, the pump is near silent after priming upon start up.

According to the 95 owners manual the low fuel light should come on with 4 gallons left in the tank... I say should because the one time I let it come on I only had 7/10ths of a gallon left according to the gas pump. Another thing to note is that the gas gauge is totally unreliable. I would stay between full and 3/4 of a tank for 200 miles then it would dive bomb towards empty. Word of advice, don't rely on the light!!!! Interesting side note, my gtp has 2 low fuel warning lights. One lights up with 4 gallons remaining (and it appears to actually be 4 gallons left) and a second light comes on if you get down to 1.5 gallon remaining. Weird considering the riv is the luxuary model of the two. Maybe they just thought us gtp owners are dumb and needed the extra reminder :p lol

They must have fixed that by the '98 model. I can use the low fuel lamp as a near 100% accurate indicator for 30 miles of mixed stop & go driving, or up to 50 miles of highway cruising. That would suggest the lamp comes on with about 1.5 usable gallons remaining. There is actually more fuel in the tank that isn't reached by the pick-up, another 1.5 gallons, I think.

I think I've only ran out one time with this car, and that was because I forgot how long the light had been on. Learned that lesson; never again.

'95s for some reason had a larger tank, so perhaps they were designed to have 4 gallons when the light comes on... my '97 goes dry at 17.5 gallons. Aaron's in the ballpark, but I think it's a little bit better than that, say 2 to 2.5 usable gallons when the light comes on.

What's even weirder than your GTP, Derek, is that everything on the Rivi dash is run by computer yet we only have that one, solid-color light. All the way back in my '81 Eldorado, the low-fuel LED had 6 distinct brightness levels... I could tell how much gas I had left down to the quart.

Reminds me of the Sienfeld episode when Kramer and the car salesman take a Volvo out and they decide to see how far they can get after the light goes on.

Also this thread gives me a chance to brag that my '95 got average 26 mpg on a 1,000 mile round trip between Reno NV and Orange County Ca. Never missed a beat, used a 1/2 quart oil, driving 70 or better most of the trip until I hit snowy conditions in the Sierras and had to dial it way back.

Have an aftermarket pump at 212k and when my lights comes on I can fill up with 15.5 gallons.

Recently I installed the Aerosport Interceptor gauge. One of the selectable display parameters is "FUEL PRCNT", which displays fuel level as a number between 7-92 (I'll explain later). This indicates the percent full. The digital display is more precise, and more responsive than the stock analog fuel gauge. This is especially useful for determining the exact level when you are near empty (low fuel lamp on).

First thing: you won't actually see a 100% value on the Aeroforce. 92 is the max value for a full tank. However, I noticed when filling up that 92 is reached a few secs before the pump handle clicks off. This indicates the float has reached its max position, which is slightly below full. When you think about it, 92% is probably about right, if you acknowledge the float's actual position in the tank. Conversely, most analog gauges show a mark for "F", indicating 100%, and it's common to see the needle go above that mark when full, indicating a value of, say, 103%, which isn't truly accurate. Personally, I have no problem with the max value of 92.

As the level lowers, the number value responds near instantly to the float position, which changes as the fuel is sloshed around while driving. Usually you'll see a variance of about +/- 2%, sometimes more if you're hard on the throttle or brake, or if in a hard turn. As mentioned, braking makes the level increase; throttle makes it decrease. Also of note: a hard right corner causes the level increase; a hard left causes a decrease. When stopped, there is no change, as expected.

When the low fuel lamp illuminates, the display reads 18-19 in my car. When this occurred, I reset the trip meter and tried an experiment. With 1.5 gal of gas in the trunk for insurance, I wanted to see how far I could go. Driving about 70/30 highway/city, I watched the display count down, approaching 45 miles on the trip. The value was "7", and wouldn't go any lower. I reached 50 miles, then 55 miles. I had found the minimum float position. Time to fill up (no, the car didn't run out of gas.

Here's a shot showing the gauges right before filling up with 17.884 gal:



Although I wish the Aeroforce would display below 7%, I understand it's only confirming the state of the fuel float, so can't blame the gauge. But I do appreciate knowing the exact fuel status after the lamp comes on. If I'm ever in a situation where I'm very low, I can monitor down to 7% - then it's time to fill up within 10 miles. For those without the Aerosport gauge, if you hit the trip reset button when the low fuel lamp comes on, you've got 45-55 miles before you run out, depending on your route and driving habits.

Note: I'm not saying people should run their fuel down to empty every time, although I usually do fill up with the low fuel lamp "on". This experiment was only to satisfy my own curiosity, and wanted to share. Removing 1.5 gal fuel container from trunk now...

i always drive until the gas light turns on lol. every time. but then thats when i start to hit it in neutral (when im gonna make a full stop anyways) .... that being said, does putting it in neutral actually save gas? thats ones of those "myths" that i never got around to checking to see if it was true

anyways i would only go up to 50 miles until i get spooked and hit the gas station. i usually don't intentionally go that long, but again with these gas prices (4.63 over here) and my current financial situation, thats just how i gotta roll lol

With fuel injection and overdrive, using neutral isn't going to save you anything... and these stupid computerized transmissions don't like it when you pop it into neutral at anything over about 20 or so.

I've seen a few fuel gauges on riv's go wack-o!

I know on mine, it sits at a 1/4 of a tank and then drops to the light shortly after
I don't mind it at all because it makes me fill up before I have one of those moments where I need to get somewhere fast.

After experiencing my fuel pump o-ring coming off, I always stay a step ahead!

With moving 500 hot miles north, I"m now more concerned with the oil in that old 430" V8...
I think the idiots that owned it before me, plus my own buying the wrong oil filter in the past (who knew they didn't have drain-back valves?!?), have caused the kind of bearing wear that Larry has warned us about...

I did put additives in the last load and the oil feels pretty thick when I dip it... I just think that I missed the right time to save the motor, and I've got mains or rods that are gonna' need work.


Given the abuse it had before, though, I don't think I'd mind rebuilding the motor to stock 430/455 specs...

Do you have a mechanical gauge in there? What do you see for pressure at hot idle? FWIW old Buick V8s have pretty low oil pressure at hot idle.

What weight oil are you using? What IS the climate you are in?

Yes, I remember reading several years ago the 430 had a weak oiling system from the factory. Otherwise a solid engine. I think it had troubles when you nailed the throttle in a corner. More info:

http://www.rowand.net/Shop/Tech/BuickOilingImprovements.htm

Thanks for the link, Aaron!

And Deek, you reminded me to update my profile!
I'll spare you the details, but for the time being I'm in Salem Oregon - which has so far turned out to be hotter than my old place on the Bay...

IIRC, I put straight-weight 30 in at the last oil change with some "motor honey". As I said, it even feels thick on the dipstick. To paraphrase Commander Cody, if I let the in-gear idle get down to 600 or 700 RPM, "down in the dip she starts to knockin'."

On the other hand, my mechanic brother complimented her on a perfect 600-mile run from Marin to Salem - and it turned out that the points and the vacuum-advance had crapped out just before I moved. 12-15 MPG...

You might want to try 20w50 for a while if it's a bit... loose. A lot of engine rebuilders ignored Buick's tighter bearing clearances and machined rods and mains like a chevy, resulting in a lot of 'low oil pressure at idle' and the recommendation for thicker oil. If the bearings were clearanced properly you should be fine with a 30. But if it's knocking at idle, get a thicker oil in there pronto!

Valvoline racing VR1 20w50 has extra zinc to help preserve your cam/lifters as well.

For the time being I think the oil's thick enough, but thanks for the zinc tip Derek.
That's something else I've been meaning to research when I have "nothing else to do"...