I'm revisiting this issue. No trouble, but it needs to be done. I'm going to measure the fuel temp as it comes from pump, and see what actual temp is in winter to see if I might get away with smaller overflow tank. I'm also curious if tank temperature reaches much above 100 in summer? I think I can tee into vent hose, and bend a hairpin upward to just below lip of filler for overflow tank inlet? If You all see any flaws in my reasoning, don't hesitate to tell my Wife, as she relishes pointing out my flaws!
I think girls get taught that in Home Economics class in high school.... Interesting you updated your thread... I was wondering if you ever pulled the trigger on this modification.
Will the volume of expansion of fuel at a lesser temperature rise be reduced in direct proportion? I'm also unsure what elevation I need to mount overflow tank for proper fill and drain.
Yes. The volumetric thermal expansion for gasoline is = 0.00053 per degree F.. So let's assume 18 gallons of gas and a temperature rise of 70 F. 0.00053 x 18 x 70 = 0.668 gallons You are changing to a non vented cap, right? Personally I would want the fitting you install in the filler hose to be below the cap so you never have to worry about removing the gas cap and gas running onto your paint again. But the fitting also needs to be located such that you don't fill the expansion tank up when you fill the tank with gas. Make sense?
Yep, I'll be using non vented cap. The vent line runs external to the fuel filler up to near the opening. If I tee into the piece of flex in the vent tube and run a tubing up and back down to the overflow tank, so the highest point is where I want peak level to be,(below bottom of filler), I think that will work. The filler neck has a 'pipe inside a pipe' that goes past where the vent line taps in, so gas can't get in the vent.
OK. Here's the "artists rendition" of the basic installation. Will this siphon the level back down to the tap point? I don't think it will be a problem if it does. Looks like it would just pull the level in the filler neck down.
Would an alternate solution be to extend the pipe-within-a-pipe down a little further, to prevent "overfilling" of the tank (I know the tank isn't huge- but does a half-gallon make much of a difference?) when fueling?
The line to the expansion tank has to be a dedicate line. This allows the gas in the expansion tank to get sucked back into the gas tank...
It looks like all I need to change is, instead of a tee in the location I showed, cut the vent line and attach the fuel tank side to overflow tank, and block off the side going to the filler neck? The short piece of rubber fuel line is a good place for that. It does look to me like once the fuel level reaches 'spill over', it will siphon gas from the tank to the overflow, probably flooding it?? With a tee, it will serve as a vacuum break. Then with a non vented gas cap it can still pull the fuel back out of the overflow tank. Y'all let me know if my logic is flawed!
Hi Wasp. At first look, that looks like it would help but I think it would only reduce the amount of possible spillage by the internal volume of that extension pipe. I'm afraid that would be insufficient. Also, it doesn't address diverting excess spillage off the paint. Thanks for the input.
The simplest solution to this is the one that worked for me as a kid. Never have enough money to fully fill your tank. Plenty of vent space. Actually, if gas prices keep climbing again, I'll be re-living it for real. Also, Bill, if you want to simulate that broke teenager, feeling, just give all but about $10, to your wife. (usually happens anyway) Then maybe she will be less inclined to point out flaws. Well... Maybe... Steve.
It won't flood it if the expansion tank is large enough. If you think about it only a small amount will auto-syphon, then it will start sucking air and stop. How big are you planning to make the expansion tank?
OK. I have a 3x16 in tank. That gives about 113 cu in of volume, or 62 fl oz. Yesterday I measured the temperature of the gas coming out of pump while filling my wife's Yukon. After about a week of low to mid 30s temperature here in the Houston area, I was surprised to find the temperature of underground tank to be 75 degrees! This is about as cold as it gets around here, so I'm using temperatures of 70 and 110 for my temperature rise calculation. This gives an expansion for 18 gallons of gas at 48 oz with a 40 degree temperature rise. My concern is that when this spill happened, the truck had been parked on the street, at an angle, so I think the amount of available gas for siphoning may be too much for the tank, but with a vacuum break, it will only need to support expansion volumes. With a non vented gas cap, the negative pressure created by running the engine will still have the desired affect of sucking the overflow tank empty.
Say what? That just doesn't seem logical. Got any volcano's in the area? Just kidding... what are you using to check the temperature? My only concern about this modification is possibility of a vapor lock... or collapsing the fuel tank. Where were you planning to put the vacuum break?
First part. I'm using a type j thermocouple input to my Fluke meter, (it has an automatic conversion to digital temp readout). Pretty good meter for $425. Second part ; If I use a non vented gas cap, the air space above The overflow tube will serve as vacuum break. When truck is run, there will eventually be enough negative pressure to pull liquid back into fuel tank? The overflow tank is vented via the standpipe which vents out the cab floor. Does this seem logical?
Yes. But How much vacuum does it take to collapse the fuel tank? and How much vacuum to vapor lock the motor? I'm probably fretting about nothing and wouldn't worry at all... if I was doing this to my own truck. But it's yours... and I'm a bit of a worry wart when it comes to other folks and there stuff.
[/QUOTE] As far as the vacuum required to pull the gas back from the overflow tank, I was going with your suggestion in this post.
