Fuel Warning Light - How many Gallons remain when comes on?

[Gr8bawana]

Back in the seventies, I believe, a certain manufacturer (not Chrysler) used a fuel return system that essentially allowed the fuel pump to run all the time. These suffered a lot of failures and the civilian theory was the pump was overheating.

Regards,
Dusty
2019 Ram 1500 Billet Silver Laramie Quad Cab 2WD, 5.7 Hemi, 8HP75, 3.21 axle, 33-gallon fuel tank, 18” wheels. Build Date: 3 June 2018. Now at 113515 miles.

What may have been true 50 years ago has ZERO relevance to what we're talking about now.

 

[392heminut]

One of my favorite of the "tall tales". If the pump sits at the top of the tank, with the pump motor protruding downward a couple of inches, after fuel quantity dips below 3/4 tank, the pump is not being "cooled" by the remaining fuel. Guess what? It doesn't need to be cooled. The rest of the assembly that IS hanging down...the pickup tube, sock, gauge parts, etc., don't do anything to aid in cooling. The real issues with running a tank too low is the air that is sucked up...cavitation. Too much cavitation leads to fuel starvation..."Out of gas" while the tank still has some in it. Read any ops manual for an airplane....They always list fuel capacity and total usable. That normally varies by a few gallons. There's a reason they list it that way.

I have to disagree with this also. Several years ago my wife had a Ford Tempo that she did a 60 mile commute each way with every day. The car would go two days on a tank of gas and be just above empty when she got home the second day, so every other day the pump would end up running uncooled by the gasoline. After about 8 months the pump started acting up and she would end up sitting on the side of the interstate 30 miles out for about 15 minutes because the car died. After 15 minutes it would start and get her home. I replaced the fuel pump and again it went about 8 months before it started doing the same thing. I again replaced the pump and was griping to a mechanic friend about how shortlived the fuel pumps were. After giving him all the details he told me the pump was getting hot and that was what caused it to eventually start shutting down. My wife started gassing up every day when she got home, only letting the tank get about halfway empty every day and the problem went away. Her commute was on I-10 in southern New Mexico, where it gets pretty hot.

 

[Dusty]

What may have been true 50 years ago has ZERO relevance to what we're talking about now.

I agree. What I was merely attempting to explain was the basis for the continued belief.

Regards,
Dusty
2019 Ram 1500 Billet Silver Laramie Quad Cab 2WD, 5.7 Hemi, 8HP75, 3.21 axle, 33-gallon fuel tank, 18” wheels. Build Date: 3 June 2018. Now at 113560 miles.

 

[2003F350]

I have to disagree with this also. Several years ago my wife had a Ford Tempo that she did a 60 mile commute each way with every day. The car would go two days on a tank of gas and be just above empty when she got home the second day, so every other day the pump would end up running uncooled by the gasoline. After about 8 months the pump started acting up and she would end up sitting on the side of the interstate 30 miles out for about 15 minutes because the car died. After 15 minutes it would start and get her home. I replaced the fuel pump and again it went about 8 months before it started doing the same thing. I again replaced the pump and was griping to a mechanic friend about how shortlived the fuel pumps were. After giving him all the details he told me the pump was getting hot and that was what caused it to eventually start shutting down. My wife started gassing up every day when she got home, only letting the tank get about halfway empty every day and the problem went away. Her commute was on I-10 in southern New Mexico, where it gets pretty hot.

Oh boy, a Tempo...that's more than 'several years ago,' my friend. HOWEVER, this illustrates what I was saying - in the early days of fuel injection, the pumps were not always sitting in fuel so they weren't being cooled - at best there was a 'baffle' in the tank around the pump in an effort to keep fuel at least near the pump. Sometime in the mid 90's most major manufacturers had switched to pump assemblies similar to what is seen today, with the pump sitting inside a canister that is constantly filled and replenished with fuel, specifically to prevent issues like what you dealt with.

 

[ReddJackson]

I was in High School in 1965, regular gas was bout.20 to .25 per/gal, during a gas war…if any of you are old enough to remember those gas was .16 to .18 per/gal…a bucks worth of gas would get me around for the week in my 1947 Plymouth.
The price of diesel now in Cali is over $5 per/gal…if I take it easy I get around 14 to 16 mpg around town, up to 20 highway with the cruise control…yes I’m a disabled vet on a pension…every nickel counts…even getting fuel at 1/2 tank is still $80 plus…more doable than doubling that…and hell no I’m not giving up my 2015 2500 RAM, yeah I drive daily and towing my camper.

 

[photoguynorth]

I was wondering the same thing, but I had the low fuel warning come on yesterday while on my way to fill it up. 26 gallon tank and it took 23.1 gallons to fill. I don't usually run to that point, I once had a car that ran out of gas before the needle even got to "E". It is good to know when the warning comes on, sometimes it is not easy to stop sooner.