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Re: Filling Habits & Gauge Nonlinearity Posted by Ari [Email]  (#2847) [Profile/Gallery]
(more from Ari) on Tue, 12 Jun 2001 16:46:23
In Reply to: Filling Habits & Gauge Nonlinearity, 94 9000 CSE T, Tue, 12 Jun 2001 16:21:03 Members do not see ads below this line. - Help Keep This Site Online - Signup |
There are a few reasons to change your ways -
First off, the pump has to work harder with a near empty tank. That will affect fuel pressure. When you first start the car, the pump has to pressurize the fuel system before the engine will catch. If it has to suck fuel up from the bottom, that's less power left to pressurize the fuel system.
Two big reasons not to run the tank low - condensation and crud. The bottom of the gas tank is where the crud falls. All gas has crud, some more than others. But unless you pull your tank regularly for a cleaning, that crud accumulates over the life of the car. When you run the tank low, you risk getting some of that crud pulled into the pump. Yes, there is a screen there, but not a great one. If nothing else, the crud can clog the screen, making the pump work harder. Crud that gets through damages the pump, clogs the fuel filter, and if some gets through the filter, hits the delicate fuel injectors.
Next is condensation. A near-empty tank isn't empty-it's full of air. If you pull in nice warm, moist air during the day, that moisture will condense on the inside of the tank at night. If you've got dew on your windows when you get up in the morning, you've got dew inside the tank. Water is less dense than fuel, so it sinks to the bottom of the tank. Not only does it rust out the bottom of the tank, if you run the tank low enough, you risk pulling in water instead of fuel. Your engine will love that. Drygas helps, but most folks don't think to put drygas in during the summer.
The gas gauge has a built-in reserve, and is biased to show you have less fuel than you really do. Empty isn't an empty tank. This is for a few reasons - first, no gauge is perfectly accurate, so Saab, (and every other manufacturer) biases the gauge low so that even with the error, you won't run the tank dry. If they didn't, some cars would run the tank dry when the reserve light just came on. Next, they don't want you to run the tank dry. That's because of all that crap and water at the bottom of the tank. Third, some systems require a few gallons of gas to reprime the system. An extra quart won't do it.
No gauge is perfectly accurate, and I don't trust the miles to empty. If it says you have 10 miles left, but there is no gas in the tank, the engine will stop. I've never run a car out, and I never intend to.
, Tue, 12 Jun 2001 17:36:15, Tue, 12 Jun 2001 16:46:23 <-- Viewing This Message, Tue, 12 Jun 2001 14:54:26, Tue, 12 Jun 2001 14:28:57
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