Clarification on Fuel Pump Return Line

[Michael C.]

I have a two-time Top Flight '77 with L-82 and M-21. It is very original and recently started to leak fuel from the fuel pump return hose right at the fuel pump. When I removed the hose to replace it I began to lose fuel from the return connection at an alarming rate. With the tank higher than the pump it would've gone on until the tank was drained. Could someone help me understand the return line and function? My perception is that if operating correctly a calibrated check valve would return fuel to the tank as needed and the fact that I am leaking with the engine off and no pressure indicates a failed fuel pump (or at least failed check valve). Am I thinking about this correctly? Thank you.

[Terry M.]

Re: Clarification on Fuel Pump Return Line

Just an idea. take the gas cap off and see if the fuel stops? Is your fuel tank full up?

[Joe L.]

Re: Clarification on Fuel Pump Return Line

I have a two-time Top Flight '77 with L-82 and M-21. It is very original and recently started to leak fuel from the fuel pump return hose right at the fuel pump. When I removed the hose to replace it I began to lose fuel from the return connection at an alarming rate. With the tank higher than the pump it would've gone on until the tank was drained. Could someone help me understand the return line and function? My perception is that if operating correctly a calibrated check valve would return fuel to the tank as needed and the fact that I am leaking with the engine off and no pressure indicates a failed fuel pump (or at least failed check valve). Am I thinking about this correctly? Thank you.

Michael-----


There's no way that the contents of the fuel tank can drain from the fuel return line. The fuel return line returns fuel to the tank near the top. In the case of 1975-77 Corvettes it's via the top-mounted fuel pick-up and gauge assembly. Any fuel drainage from the line when disconnected at the pump should only be any fuel which happens to actually be in the line.

[Edward J.]

Re: Clarification on Fuel Pump Return Line

I would say Terry has the right idea, with the gas cap on ,The system is sealed and the residue pressure in the tank maybe force feeding the fuel down the line. once you removed the line the fuel in line starts a siphon. just a thought.

[Clem Z.]

Re: Clarification on Fuel Pump Return Line

it is a calibrated leak back to the tank. if you block that line you will up the fuel pressure and this comes in handy if your fuel pump starts to go bad you can get home by just blocking the return line.

[Joe L.]

Re: Clarification on Fuel Pump Return Line

I would say Terry has the right idea, with the gas cap on ,The system is sealed and the residue pressure in the tank maybe force feeding the fuel down the line. once you removed the line the fuel in line starts a siphon. just a thought.

Edward------


The tube inside the tank for the fuel return line is only about 2-1/2-3" long. So, in most cases, there is an "air gap" between the bottom of the tube and the fuel level in the tank. Thus, pressurization, or not, the fuel will not be forced out the return line. If the tank were exceptionally full, the end of the tube might be submerged in fuel and, thus, siphoning could occur. However, it would only continue so long as the tube was submerged.

[Edward J.]

Re: Clarification on Fuel Pump Return Line

Joe, In the post the fuel was coming from return side could it be that the pump side was leaking when hose was removed. I believe the supply line at pump maybe able to suppy the fuel over to the return at the pump?

[Michael W.]

Re: Clarification on Fuel Pump Return Line

I interpret the OP's message as saying that the fuel is leaking out of the pump fitting, not the return line. If this is the case, this flow would be normal. The pump has no check valve to prevent such leakage.

[Michael C.]

Re: Clarification on Fuel Pump Return Line

Sorry for not making myself clear. The fuel is leaking from the pump out of the fitting that takes fuel back to the pump. At this time I have no leaks at the tank; the issue is at the pump.

The hose connecting the pump to the steel return line failed and drained fuel out of the tank. I wanted clarification as to whether or not there was a check valve or other device in the pump that would keep tank from draining and if such a leak was an indication of a faulty pump. It appears not.

Thanks.

[Michael C.]

Re: Clarification on Fuel Pump Return Line

"The fuel is leaking from the pump out of the fitting that takes fuel back to the pump". Meant to say "takes fuel back to the TANK".

[Edward J.]

Re: Clarification on Fuel Pump Return Line

Mike there is no check valves in your corvette fuel pump. It is a tough thing to replace those fuel line rubber hoses with fuel in the tank as once the fuel starts flowing its will drain the tank. If you can access the rubber hoses at tank in rear you coulc pinich they off.