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  #1  
Old 01-08-2005, 10:15 PM
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Keep the gas tank full in cold weather?

I live in Wisconsin, and every time the weather gets cold people tell me to make sure I keep my gas tank full. When I ask them why they don't have an answer. Why do people always tell me to keep my tank full in the winter? Does it have something to do with condensation forming in the tank? Is it just so there's more weight in the back in case it snows? I've been wondering about this for years. Can someone explain this to me? Thanks.
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Old 01-08-2005, 10:27 PM
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And do they tell you to keep your tank empty when the weather is hot? When everything is at the same temperature (air, fuel, metal), there is no condensation (hot or cold)
fairy tail, urban legend, myth, folklore.
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Old 01-08-2005, 10:33 PM
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I'VE been told condensation of the tank's air moisture will freeze and block the fuel line.
the more full the tank,less air less moisture.

one would assume if the car is warm up the inside of the car's temp is different from the outside.

on extremely cold days,my car window also ices up from condensation on the inside.(when i lived in manitoba).Can the same thing not happen inside the fuel tank?
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  #4  
Old 01-08-2005, 10:48 PM
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Quote:
Originally Posted by Jackd
And do they tell you to keep your tank empty when the weather is hot? When everything is at the same temperature (air, fuel, metal), there is no condensation (hot or cold)
fairy tail, urban legend, myth, folklore.
Good point. I agree that you need a temperature differential to induce condensation.
I also believe that you need air space to allow water droplets to form from the air and attach themselves to the tank wall. So filling the tank will minimize the available air space.
So might it be that gas tanks mounted outside the heated interior and adjacent areas probably wouldn't condensate as much, if at all, as a typical Mercedes tank mounted inside the trunk?
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  #5  
Old 01-08-2005, 10:50 PM
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Petaling:
Condensation only happens when water vapor is in contact with a cold object.
Air moisture in the tank (if any) is at the same temperature as the fuel, the fuel tank and outside air. There is nothing to heat the fuel tank or its surrounding.
Condensation in the inside of your car window comes from the fact that the inside air (including moisture from your breathing) is warm as compared to the glass.
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Old 01-08-2005, 10:53 PM
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You mean sunoco's fuel with ethanolm PetroCanada's winter gas,and gas line antifreeze are all scam??????
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  #7  
Old 01-08-2005, 11:23 PM
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Just for thought........

The fuel in the tank is constantly being recirculated. It heads for the injectors and is returned to the tank at a pretty good flow rate. The fuel on the way back is warmer then the fuel on the way out. It is conceivable that the tank is 20 degrees warmer than the ambient air. This would be especially true if the level of fuel in the tank is low.

I wouldn't be too concerned about it if you consume a tank of fuel within ten days or so. But, if this time is exceeded, and the vehicle has quite a few cold starts, the warmer fuel could present condensation issues.
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Old 01-09-2005, 10:13 AM
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I don't know about all MB's but on my 84 500SEL the trunk and fuel tank is heated from the air flow through the car. I haven't actually checked the heat in the trunk but I did once check the temperature in the trunk during the summer. Inside the car the temp was 78 degrees, inside the trunk it was 88 and outside was 94. So I guess the same could be true for heating in the winter and the fuel tank is in the trunk. On a long drive, the fuel could be quite a bit wormer than the outside temperature.
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Old 01-09-2005, 12:05 PM
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Jack(knife)d
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Old 01-09-2005, 01:18 PM
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I would imagine, taking a car from cold temperatures & parking it in a heated garage, would have to result in some condensation.
Keeping a tank fairly full, to minimize condensation & increase traction, makes good sense to me but hey, to each his own.
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  #11  
Old 01-09-2005, 01:19 PM
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inetd:
Quote:
When warm air vents into a half-full fuel tank, it meets the cooler fuel and quickly condenses, releasing moisture either in a sublimation or vapor to solid form
Where's the warm air coming from????????
When my car sits in my driveway at -35C, the fuel is at
- 35C, the fuel tank metal is at -35C and any air coming into the tanks from the vent is at -35C. In our climate, you don't replace the volume of burnt fuel by warm air. Water condensation will only occur when and if warmer air containing moisture comes in contact with a cold surface (fuel or fuel tank walls).
Quote:
when cooler air holding very little moisture contacts warmer gas, it's no big thing
Exactly my point. If the fuel is being warmed (by circulation through the fuel injection system or other source of heat) and colder (dryer) air gets into the tank, replacing the volume of fuel consumed, it's no big thing.
Quote:
luckily for me the MB design left the fuel pickup slightly higher than the bottom of the tank
This is not a MB proprietary design as all car manufacturers have been building their fuel tanks this way for ages.
Most of the water contamination seen in fuel tanks comes from distribution terminals and service station tanks, not from condensation in the car's tank.
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Old 01-09-2005, 01:46 PM
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one other reason to keep the tank full on an MB in the winter is that it increases the traction on the rear tires ...
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  #13  
Old 01-09-2005, 10:43 PM
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I agree that this adage is mostly urban myth, but wouldn't one get condensation on the rare case where you filled up on a warm, humid day, then the weather turns bitter cold, as it's happened here recently. During the last warm spell we got the dew point went up near 60. Everything in the garage was wet... the floor, my car, my tools... everything that was chilled. Should that humid air have gotten into the tank, I'm sure it would have condensed now that temps are back in the 30s.
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Old 01-10-2005, 11:50 AM
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Many urban car myths continue to circulate despite advancements in system design, materials, and technology...this is one of them.

Moving the fuel pumps to the gas tank area (whether it be adjacent or inside), effectively eliminated the freezing fuel lines in winter and vapor lock in the summer.

However, I feel it's good practice to keep the tank moderately filled at all times. Finding yourself stranded in in a winter blizzard or an 18-mile traffic jam on a stretch of highway with no exits, makes you glad you went ahead and topped off!
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Old 01-10-2005, 12:09 PM
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I make sure mine is full before it snows, because I want the weight of the fuel. My tank is right above the rear axle, and since the SDL doesn't have a limited slip I need all the weight I can get back their.
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Old 01-10-2005, 12:09 PM
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