lobuxracer

iTrader: (2)

Bench test dry - immediate damage

Run dry on fuel - engine stops, and ECM shuts off fuel pump until STA is active.

Big difference.

Kurtz

iTrader: (1)

Absolutely true.

Now... run on enough fuel to half-cover the pump instead of immerse it like it was designed for... pump still runs... and runs hotter than it's meant to.

It's not going to immedately die. It might not die if you consistently do this every tank of gas for 100k miles even. If you're lucky. But over 200k? Or if you're not lucky?

Why take the risk of shortening the life of a reasonably important part just to go an extra few miles between fillups? It's not like it costs any more (besides the couple extra minutes to put gas in).

Bichon

Plus, we're not even talking about running out of gas. We're talking about driving 10 or 20 miles after the light comes on, at which point there is still well over a gallon of 'reserve' gas left. On my car, when the light comes on, the car will take 14.9 gallons to fill; the tank has a 17.1 gallon capacity.

Bichon

My '84 Accord went over 240,000 miles on the original fuel pump. Long enough to go through a couple of starters, alternators and an A/C compressor, but despite lots of driving on "E", the fuel pump soldiered on.

Kurtz

iTrader: (1)

Yes, and we all know folks who drove 100k miles barely ever changing their oil too, it still doesn't make it a good idea.

By all means, it's your car, if you want to ignore a slew of people who work on cars or give car advice for a living and run your cars on/near empty all the time- do it.

You might never have a single problem.

Or you can stop for gas slightly more often, at no extra $ out of your pocket, and be safe.

Your call.


BTW, for the car talk guys agreeing with me, see here:
http://www.cartalk.com/content/colum...bruary/09.html
"modern cars have fuel pumps that are submerged inside their gas tanks. And since the gasoline acts as their lubricant and coolant, you can do damage to the fuel pump if you run the tank dry."

Actually, here, they mention it again-
http://www.cartalk.com/content/colum.../March/04.html
"And the reason your fuel pumps are failing is because you're running the tanks dry. The gasoline in the tank actually serves as a coolant for the submerged fuel pump. Without the "coolant," you're running the pumps hot and burning them out prematurely."

Or here:
http://www.cartalk.com/content/colum...01/May/08.html
"When the tank is near empty, you're depriving the pump of its coolant, which is the fuel that it bathes in."

Or here-
http://www.cartalk.com/content/colum...August/09.html
"the car's fuel pump lives in the gas tank and is cooled by the gasoline. And they'd feel just terrible if you ran out of gas and burned out the fuel pump -- especially while the car was covered by THEIR warranty. "


They mention the specific 1/4 full recomendation here:
http://www.cartalk.com/content/colum...8/June/04.html
"One is that on most cars, the electric fuel pump sits at the bottom of the gas tank. And the gasoline actually serves as the pump's coolant. So if you drive around with the needle on "E," you're allowing the fuel pump to run hotter than it should, and potentially shortening its life."

Or a slew of other places they mention this... Plenty of other folks recommend the same thing, but I figure folks who've spent decades being paid for car maint. advice might carry some weight.

Bichon

At the risk of beating this dead horse to a bloodier pulp than it already is, I'm not talking about running the tank dry. (which is what Click and Clack caution about) Fuel pump aside, I don't enjoy long hikes carrying a gas can nor calling up roadside assistance. I'm talking about filling the tank soon after the warning light comes on, which means somewhere between 1-20 miles of driving on the 2.2 gallon reserve.

By the way, I calculated that if I were to fill at 1/4 tank instead of empty, given an average of 1.5 fillups a week over my 30 year driving career, I'd have made an additional 585 trips to the gas station.

Kurtz

iTrader: (1)

Well, you probably drive a lot more miles than I do... I fill up once a week usually, prob. 50 weeks a year... so 50 fillups a year. If I let it go to empty I'd presumably fill up about 38 times a year instead.

So somewhere around an average of one extra stop at the station a month... at maybe 10 minutes tops per stop...

That's 2 hours a year I invest in not worrying about my fuel pump... or a little under 2 total days in my entire driving life.


I'm not suggesting your fuel pump explodes at 1/4 tank minus one drop, it's just a pretty good, and easy to notice, point to fill up at.

This is especially true in a couple vehicles I've had where the design of the tank was wide/long, and fairly flat... where fuel sloshing on a quick stop or take-off could swing the gauge between a bit over 1/4 to barely above empty.


It's kinda like letting your car warm up a bit before romping on it. Some folks have no problem keeping it under 3k rpms for the first few minutes... other people don't care to "waste the time" and punch if right away.

Both cars'll probably run decently long. One'll just probably run longer.

If you replace your car every 50k miles or whatever you aren't gonna care either way. If you like to keep your cars till they die, you might find the couple extra minutes worth investing. Same with filling up slightly more often.

lobuxracer

iTrader: (2)

And again, product specific knowledge is paramount. This is from the 1993 Supra New Car Features. Toyota know how to address these issues, and they do very consistently. As you can see, the fuel pump is used to continuously bathe itself regardless of tank level.

lobuxracer

iTrader: (2)

And here is IS350 specific information - again, Toyota have addressed the issue in a way other manufacturers have not:

Kurtz

iTrader: (1)

That subtank is a pretty clever system for addressing this issue... thanks for the diagrams. Is there any information in there on the capacity of the subtank? That'd give us an indication how just how low is "safe" under this design. I have actually replaced the fuel pump on a supra before, but it was pre-93 so that'd explain how I missed the feature. I imagine if I ever need to get into the one in the SC300 we have it'd look that way though.

lobuxracer

iTrader: (2)

No documentation on the volume. I do know that when the light comes on, it's definitely time, and you'll "run out" before you actually run dry because of the subtank system. That's why I take the light pretty seriously, and I never plan to run completely dry, even though I know it won't really hurt anything, I hate driving a car while it's purging the fuel system.

With the returnless systems like we have it shouldn't be so bad, at least the air bubbles go into the tank, not into the line, but if you run the line dry, I have no idea what kind of sputtering and coughing it might do on refill and restart.

rfx45

Thanks for all the great, detailed info. I guess I'll do my best to try and fill it up when the computer says 5-10 miles left.