The Stovebolt Site Forums The Shop Area Engine Shop 53 Fuel Feed - Top or Bottom?

Hi all - I'm replacing my fuel tank on a '53 truck (leaving it behind the seat) and considering switching form a gravity feed (bottom) to a top feed (through a '54 sending unit). But as I'm thinking about the "why" the common response I find is: "if the fuel line breaks on a gravity feed, it'll drain the tank, top feed is safer!"

But is it?

Once you've primed the siphon action of a top feed, assuming the fuel line exits the floor below the tank if you break the line just below the tank, won't it siphon out the entire tank anyway?

Another example: Let's say the fuel line breaks at the fuel pump -- a point that is (let's say for argument) about as high as 1/3 up from the bottom of the fuel tank: In a gravity feed system, the fuel will be pressed out the bottom until the tank is 1/3 full, then stop. In a top feed system, won't the fuel be sucked out of the tank until it's about 1/3 full also?

Science says that's right.

I prefer the top feed setup. It comes with a replaceable filter sock at the end of the pickup tube on the sending unit assembly. I don't like the bottom feed setup due to the way gravity places any loose crud directly into the fuel system.

Yes, the top feed will drain out on a broken line. I went to a top feed on a 49 when I traded for a new tank that wouldn't accept the bottom feed on/off valve. It came with a new top feed sender w/filter sock. I had reservations as I didn't know I the fuel pump would pull through a top feed. It will.
I had to remove the fuel pump to carb line for servicing and the fuel continually dripped through the fuel pump into a catch can I placed under it until I hooked the line back up.

The 2" or so of tank depth below the top feed pickup tube also serves as a water trap so condensation doesn't get into the fuel system. It's also a good place for sediment to collect rather than ending up in carburetor jets, fuel pump check valves, etc. In the winter when condensation might become an issue, adding a pint bottle of 91% rubbing alcohol to the tank about once a month is a lot cheaper than a can of Dri-Gas, and just as effective in keeping the condensation to a minimum.
Jerry

Sounds like a resounding case for Top Feed... Thanks!

Just a question. With bottom feed wouldn't the condensation work it's way out of the tank as it forms and thus not corrode the tank anyway?

Condensation can't really work it's way out, but you would tend to get more water headed to the carburetor.
On my first Model A, I had a problem with rust flakes in the tank getting into and clogging the filter bowl and wound up putting a small standpipe on the outlet valve to keep from drawing fuel from the very bottom of the tank. I don't have that car anymore, but I wouldn't be surprised if that standpipe is still in place.