Who is responsible for putting the fuel pump INSIDE the fuel tank?

Dear Car Talk

Dear Car Talk | Oct 01, 1994

Dear Tom and Ray:

Could you please print the name and photograph of the engineer (or bureaucrat) who is responsible for putting the fuel pump INSIDE the fuel tank? I want to see what that moron looks like and I want to put a curse on him and his family. Until recently, it took about 20 minutes to replace a fuel pump and cost about 30 bucks. Now it takes a full day in the shop and it costs a fortune. To what advantage?

TOM: To what advantage? To OUR advantage! We make 40 bucks an hour changing fuel pumps. This is progress!

RAY: Actually, Leslie, the evolution of the fuel pump is pretty interesting. In the old, old days, the gas tank sat in front of the driver--right on top of the engine-- and had a tube in the bottom of it. The gasoline just dripped down into the engine. And gravity was the "fuel pump!"

TOM: Later on, mechanical fuel pumps were bolted onto the engine, and would "suck" fuel from the gas tank (at the back of the car) up to the engine. And when engines had carburetors, that was good enough. The mechanical pump was driven by the camshaft; so as the engine went faster, the fuel pump pumped faster. It wasn't very sophisticated, but it kept the carburetor bowl full, and that meant there was always gasoline there if you needed go fast.

RAY: Modern cars, on the other hand, have fuel injection. And fuel injection requires that the fuel be under higher, AND more steady pressure all the time. And if that pressure is lowered or interrupted for any reason, even momentarily, the engine won't run. Thirty-dollar mechanical pumps couldn't provide high enough or constant enough pressure for fuel injection, so fuel injected cars switched to electrical fuel pumps.

TOM: Then another problem cropped up; vapor lock. Vapor lock is an annoying hot weather problem in which the gasoline in the fuel line gets so hot that it vaporizes. And when it vaporizes, the car won't run because the fuel pump can't pump vapor.

RAY: So manufacturers solved the vapor lock problem by moving the fuel pump inside the gas tank, and submerging it in the gasoline. Since the pump is always surrounded by liquid gasoline, it never has to worry about pumping vapor, right? And by "pushing" the fuel under pressure from the tank all the way to the fuel injectors, the gasoline never has a chance to vaporize in the fuel line and cause problems.

TOM: So that's how fuel pumps got from $30 to $300, Leslie. And you're right, it is a pain in the butt when you have to change it. But the advantages of fuel injection--better fuel economy, lower emmisions, more reliability--are worth it to most people. Although obviously you're not one of them.

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