Gas: Full up or half a tank???

KnuckleBuckett said:
Is it good practice to remove the battery?



What should be done to preserve tires?
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Todays cars it may be a bad idea as many have computer related devices and by removing the battery, you run the risk of getting a fault that a dealer may have to clear.

As long as the battery is vented with a vent tube, leave it in the car and put a maintainer on it. Good ones will not boil the battery. Don't go cheap on the maintainer.



Inside, trunk, engine, add bags of desiccant and baking soda inside to pick-up odors and moisture. If you have rodents, check all places where they could enter and seal them. I also put steel wool or plastic on all engine openings (exhaust, intake etc). Mothballs in an old sock works well or peppermint oil in a container keeps them at bay.



Condition the body seals and rubber. Any good rubber conditioner. I use 1Z Gummi Pflege for rubber and Cockpit Premium for vinyl/plastic etc.



Tires: Increase tire pressure about 10-15 lbs above the recommended pressure and check every few weeks. Most cars are shipped with tires inflated very high, in my case 60Lbs. I also use Tire Cradles so the tires do not flat spot. Or roll (not start) the car a little every month. You can use a good rubber conditioner just to keep them clean.



Wheels, make sure ALL brake dust is off before storage and protect with wax or a sealant. Brake dust is corrosive.



I change the oil and filter before storage as well, it gets rid of additional moisture and acids from use that season. DO not start it when in storage. It just does not give the engine enough time to fully come to temp and burn off acids and other harmful agents. It also contaminates the nice clean oil you put in.



Once ready for start of the new season, I remove all blockages (wool, socks etc) check the car for rodents. Then, remove the fuel pump relay and crank the engine until you see oil pressure. Then re-install the relay and run at idle. Check for fluid leaks. Adjust tire pressure to correct settings. Brakes may not have the highest braking efficiency after long storage. Go easy and apply brakes several times at nice, low road speeds. Drive it below 3K/4K RPM until it's fully warm.



Hope this helps.



Regards,



Deanski
 
I'm not quite sure I understand how air gets into a gas tank as the amount of gasoline goes down. I'd think the only time it gets in there is when you fill it? As the gas level goes down, fuel will vaporize to fill the void. I don't think rust is a problem anymore from low levels either, as most tanks have plastic liners.



I'd think the benefit of less weight is fairly trivial. We are talking maybe 50 lbs here, unless you are going to keep the tank at an 1/8 or less or something. Going to the gas station twice as often would seem to me like a pretty big negative for this scheme, though.
 
Aurora40 said:
I'm not quite sure I understand how air gets into a gas tank as the amount of gasoline goes down. I'd think the only time it gets in there is when you fill it? As the gas level goes down, fuel will vaporize to fill the void.
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You're kidding, right? Oh...you're an electrical guy, IIRC. No, if you pull the gasoline out you're going to reduce the pressure in the tank to subatmospheric, simply because you are reducing the volume of the liquid in the tank. If you want to change the phase of the fluid as you suggest, you'll need to increase the temperature. Tank systems always have breather vents to equalize the tank pressure to atmospheric (within a certain tolerance) to account for liquid level changes and pressure changes caused by temperature changes. This prevents explosion or implosion of the tank, or overflowing, as well as providing a (relatively) constant suction pressure at the fuel pump. In the automotive application, the vapor recovery cannisters are hooked into this system to absorb the gasoline vapors.



It's the same principle as holding your finger over the end of a straw that's in a glass of liquid and pulling the straw out--as long as you keep your finger over the end of the straw the liquid will stay in there--but as you vent the tank by taking your finger off the end, the fluid will flow out...the same thing would happen in your gas tank if you didn't breathe air into there to replace the volume of gas being pumped out, the tank pressure would go subatmospheric (pulling a vacuum), the pump would cavitate (possibly damaging the impeller)...the car would stall from being fuel starved.
 
Setec Astronomy said:
You're kidding, right? Oh...you're an electrical guy, IIRC. ....
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Hey, wait a minute! I’m an electrical guy, and they made us take physical chemistry, thermodynamics and fluid mechanics.



I know how to drink a milkshake through a straw and everything! Well, not at Wendy’s. At Wendy’s I have to use a spoon.





PC.
 
KnuckleBuckett said:
Pump readout feedback is calculated using the feedback port (kicks it off when full). The higher the speed the more that air in venturi form (zipping past the feedback port) increases readout error. In effect you are paying for air. Further, though to lesser effect, the higher the fill speed the more air is incorporated into the fuel (temporarily) thus again you are paying for air. An exagerated example of this would be whipped cream.
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But what if the error was in my favor?



;)
 
Personally, I will drive until the light comes on, or just before it. I try not to run the vehicle to much further after the light came on since most fuel pumps nowadays use the fuel to lubricate and cool the pump. Either way, I don't think it really matters, but I'm a believer in running your vehicle too low too many times can reduce the life of the pump.
 
the other pc said:
Hey, wait a minute! I’m an electrical guy, and they made us take physical chemistry, thermodynamics and fluid mechanics.



I know how to drink a milkshake through a straw and everything! Well, not at Wendy’s. At Wendy’s I have to use a spoon.
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I can't eat a whole Frosty anymore, it makes my teeth hurt. Eh, I learned about straws from reading the back of cereal boxes, anyway. Do you know how many straws you would have to lay end to end to reach the moon? Me neither.
 
Setec Astronomy said:
If you want to change the phase of the fluid as you suggest, you'll need to increase the temperature.
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Well, I do know that pressure will dictate a phase change just the same as temperature will. I believe gas caps only vent one way, and that is simply to prevent the pressure from getting too high in the tank (this is why many states test the cap when doing an emissions test, to make sure it isn't venting at too low a pressure).



I absolutely don't understand why it would starve your motor. The pump is in the liquid, it isn't at the motor using suction. There could be total vacuum in the space above the liquid gasoline, and the fuel pump would still work just fine.



But yes, lol, I'm an "electrical" guy I suppose.
 
Yeah, you're going to lower the boiling point of the fluid, yes you will get some vapor to replace liquid as you draw down the tank. From my 1976 Buick Factory Service Manual, in the description of the evaporative emission control system:



3. To prevent the tank from mechanical damage in the even of excessive internal or external pressures resulting from the operation of this closed system, a pressure-vacuum relief valve, located in the gas cap, will control the tank internal pressure.



If the state only checks the cap for pressure relief, it's because they don't care if your car stalls, only if it barfs out vapor or gas.



Here's one online reference that discusses why you need to relieve the vacuum on the tank for structrual reasons Tank protection division - storage tank venting for conservation, safety, and environmental protection
 
I could see how a 1976 Buick might stall as it probably had a mechanical fuel pump mounted on the motor. But do you agree an electric pump submerged in the fluid would not suffer that problem?



I wouldn't think vacuum would hurt a modern gas tank, but I don't really know that. Maybe the gas cap does also allow air in. If you drove the car regularly and only filled up to 1/2 a tank, I doubt condensation or water in the fuel would be a problem because of this though. It just seems like the benefit of doing this is pretty dubious and it would be quite a hassle to have a driving range of like 150 miles.
 
I only used my '76 manual because back in those days the manuals actually explained how the systems worked. And no I don't agree that an electric centrifugal pump is different than an engine-mounted diapraghm pump, you still won't pump anything out of the tank if you don't vent the ullage. Even those college kids who punch a hole in their pressurized beer can have to open the tab before they try to drown themselves. And don't look at me on the half-tank stuff, as previously mentioned I run mine down to nothing then fill it all the way back up. Anyway, that's enough on this subject.
 
jtford95 said:
If I'm not mistaken, you get better gas mileage with a full tank of gas.
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What's the concept on that one? Or is that only if you have one of those magnetic vortex fuel straighteners that aligns the fuel molecules so they spray thru the injector in an orderly fashion?
 
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