I didn't want to hijack the thread about fuel starvation on a hill due to low fuel level but feel compelled to respond to one persons solution of pressurizing the fuel tank with exhaust gas by connecting the exhaust pipe to the fuel tank with a copper line. It has been discussed before but many folks are new to the forum and for those I would like to make an argument against this practice.
Pressuring a fuel tank with exhaust gas is typically used in model airplanes, but those engines do not use gasoline. Model airplane fuel is a fuel oil mix that is far less explosive than gasoline. Because it works on model airplanes does not mean it is a good idea for an automobile. I know a few people have done this and not had a problem, but just because they haven't blown themselves up yet is not a compelling argument that it is safe. I know people that have chain smoked their entire life and never had cancer, drink and drive and have never had an accident because "they are extra careful when drunk". I have seen people smoking while pumping gas, keep their engine running at the pump, even get in and out of the car while pumping gas, regardless of the safety signs posted, and have never seen anyone blow themselves up, and I hope I never do. but it does not mean it is a safe practice. I have had an explosion in the muffler once or twice in my 45 plus years of owning a model T, strong enough a backfire that it actually blew off the end of the muffler, so much for inert carbon monoxide preventing combustion. Another thought is when the car is sitting for some length of time, days, weeks, months, and some fuel in the tank turns to gas in the closed fuel system, the fumes are going to follow the copper line to the exhaust pipe and accumulate there. Starting the engine under those conditions could be disastrous.
I am also against the use of oak for spokes, leaving original babbitt thrust washers in the rear axle, keeping the original plate glass, and not having an electrical fuse. I will also state although I personally wouldn't, I have no issues with those who want to use a water pump, special engine oil, 12 volt electrical, alternator, flat tube radiator, turn signals, LED lights, and so on, but tapping the exhaust into the fuel tank is making a bomb...in my Humble opinion, others may disagree, your mileage may vary.
The exploding muffler is caused when the ignition momentarily falls and the muffler is filled with unburned air fuel mixture.
You do realize that to have combustion you need a air- fuel ratio of no richer than 10-1 and no leaner than 14-1
Pressurizing the fuel tank can be made quite safe by following these guidelines;
Put a simple swing type check valve in the line so the flow can only be from the exhaust to the gas tank.
Build a simple “flame arrestor” by inserting a bit of “metal scrubbing wool” into some of the pipe
Probably both of these are unnecessary, but cost very little for some extra safety
Now to REALLY scare you;
When I have to soldier a gas tank, I make sure to leave some gas in the tank and then warm up the tank in the hot sun. I want to be able to see fuel vapors rising from the tank filler. Yes I only do this outside and prefer a warm day. I turned 69 today
I have welded up fuel tanks by filling the tank with argon. This was after cleaning it out with soap and water.
When I was in high school I worked in a truck stop. One day a mechanic was welding up a gas tank in the back of the shop. A prankster, not me. slammed down a board which made a big noise and lots of dust. The guy welding the tank wanted to kill him.
Friend was going to weld up some pin holes in a cycle tear drop tank, soap & water repeatedly. Said he couldn't smell a thing. Brought the flame to the tank and it disappeared! Went straight up about 100 feet. One of the others there spotted it and yelled out. All ran in every direction. Came straight down about 2 feet from where it left. Split wide open like an angry clam.
OH, by the way, that pressureizing with exhaust sounds nuts to me.
Neil K and Charlie B, Good stories! Thank you. Absolutely, gasoline tanks and anything hot might be a very bad combination. There are ways to safely weld gasoline tanks if they need it. But one needs to know the "tricks", and beyond knowing the "tricks", develop an understanding of what happens and why.
“I’ve done it a hundred times” stated a local fellow, as he started to cut the top off an empty 55gal drum. His grieving family had his funeral 3 days later.
What you have described above has no relation to the system used to supply exhaust pressure to a fuel tank.
The pressurising using exhaust gas was a well know system used in the early days of motoring. The system is not just a copper pipe from the exhaust pipe to the gas tank.
A specific unit designed to connect the pipe from the exhaust contain a one way valve as well as a filter which prevents any flame from being able to pass through it. Because of the length of piping involved the exhaust gas is not hot and ignition of the fuel vapor is impossible.
After researching this method of pressurisation I installed a system in my speedster which has been there for several years. It not only works but is a period correct system.
Here is a period article originally supplied by a forum member
What's a backfire?
Cadillac used exhaust gas fuel tamk pressurization.
Exhaust gas contains little or no oxygen.
By the time it got back to the gas tank,it was just cool,inert gas.
Even if you were running rich,what would more gas fumes hurt?
Some pre-T Fords used exhaust pressure to run their oilers.
I possibly still own one of those oilers.
Another option could be to use a vacuum tank. I helped a friend with a 1925 Chevrolet 490 and it worked quite well. The tank was mounted high on the firewall and connected to manifold vacuum which drew fuel from the actual gas tank. When the vacuum tank was full of gas there was a return line I believe or a float valve set up to prevent too high a gas level in the vacuum tank. The actual gas tank was located between the frame rails at the very back of the car. Gravity delivered gas from the high mounted vacuum tank to the carburetor.
My 27 Chevy had a vacuum tank. They work well when they work. A float cuts off the vacuum and opens a vent. When empty you have to fill them up to start the car for the first time. There is a bottom chamber that gets filled by the top chamber and is always at atmospheric pressure so the carburetor does not get starved. There is a one-way flap valve between the top and bottom chambers. Vacuum leaks will kill a vacuum tank.
My ’26 Buick had a Stewart vacuum tank. Worked great except when the engine was laboring to go up a hill and the vacuum tank decides to take a “drink”. There would be a momentary loss in power as the vac. tank was being refilled, this at a time when you really need it.
Think of vacuum wipers when you're under a load. Now with age, the "pot metal" parts of Stewart vacuum tanks are suffering the same decay that's affecting "babbit" thrust washers. Often the parts self-destruct, first showing crazing and then becoming unsound and crumbling into bits. I don't know where to find them, but a few years back someone was reproducing Stewart parts in brass.
Rich, There was a source in Australia producing the Stewart vacuum tank castings and they were pricey at $250 or more. Gasket kits, springs and screws are readily available. The quality of the Stewart pot metal seems to be a bit better than some others I have seen. The pot metal on the ’26 Buick’s vacuum tank was in great shape after 90+ years.
I am trying to imagine how steep the hill would have to be to need something like this. My 25 would be like most cars, and I have had it on some very steep hills (desert trails). I know some of the cars used a rectangular tank in the trunk, and they may be effected sooner than the 25. My 14's tank is in the same location as the 25, so I am not expecting any problems with it either. On my race car I put the tank up front for safety reasons,and it works very well, up or down hill.
My 1905 single cylinder Cadillac used hot exhaust gases to pressurize the oiler to force oil into the crankcase. In later years Cadillac used the same exhaust gases to pressurize fuel tanks.