I am about to install a lift pump on my 2001 duramax. I assume the 3/8" line is the feed line to the motor, and the other line, which is closer to 1/2", must be the return line to the tank. Am I correct? If so why is the return line larger than the feed line, I don't think it is possible to return more fuel than that is being sent.

I am about to install a lift pump on my 2001 duramax. I assume the 3/8" line is the feed line to the motor, and the other line, which is closer to 1/2", must be the return line to the tank. Am I correct? If so why is the return line larger than the feed line, I don't think it is possible to return more fuel than that is being sent.

You got it backwards.

Jim

IF so, then what is the cooler for.

When adding a lift pump, is it installed in the feed line or the return line? On Kennedy's website it looks like it is in the return line, right above the cooler, that's if the 3/8" line is the return line. any help?

the cooler cools the fuel on the way back to the tank after being used to cool the fuel injection system.

When adding a lift pump, is it installed in the feed line or the return line? On Kennedy's website it looks like it is in the return line, right above the cooler, that's if the 3/8" line is the return line. any help?

I can't find the picture your talking about. But I think John dropped his tank and took off the feed line that goes between the tank and the line on the rail. I think he plumbed the lift pump there and just mounted it by the fuel cooler. It makes no sense to plumb a lift pump on the return line from the engine. You want to "lift" the fuel up to the pump on the engine and over come the filter restrictions.

Jim

Jim is correct.. JK plumbs his lift pump between the Tank sender nipple and the 1/2 inch hard line above the fuel cooler. (I plumbed my setup (http://community.webshots.com/album/77018086bLHHHC) this way too). JK's custom pump fittings also make these conections very easy.

See the following link for more info.

http://www.kennedydiesel.com/docs/liftpump_installation_options.htm

http://www.dieselplace.com/forum/smileys/Geek.gif

I have seen the lift pump installed on the supply line. its easy to locate. the line not going to the cooler.
Ithe cooler is used to "cool the fuel"but the have found in places of extream cold the cooler will ice up with snow and the fuel will wax up.