Saddle Tank Fuel Line Routing???

[SavageC20]

My 72 C20 has two aftermarket saddle tanks installed on it. I currently have them bypassed and am running on the stock tank in the cab. There is an old Stewart Warner electric fuel pump (model 240a I believe) under the cab. I am trying to figure out how these lines were routed and how it all works. Does the electric fuel pump fill the stock tank from the saddle tanks? What role does the three way valve play? It's my first time dealing with something like this.

Also, is this fuel pump worth rebuilding and running?

[kwmech]

All the trucks I've had with saddle tanks just used a gravity feed system with the 3 way valve

[SavageC20]

Originally Posted by kwmech

All the trucks I've had with saddle tanks just used a gravity feed system with the 3 way valve

Yeah I don't really see a need for the fuel pump. I wonder why it was on there? Maybe to transfer fuel to main tank? Does anyone have a diagram of something like this?

[B. W.]

There is a diagram in the factory manual - I think it's in the service manual but it may be in the assembly manual, can't remember.

Use the search bar, select our site, not google. Go to images, there's some pics of the hose routing.

[Steeveedee]

The hose from each saddle tank and the main tank are routed to the transfer valve, and one line goes to the fuel pump. On my truck, there were rotten neoprene fuel lines running up over the driveshaft, held up by zip-ties. I converted them to steel lines for the up and over part. I have an electric fuel pump on my truck between the transfer valve and the fuel pump, to defeat vapor lock if it rears its ugly head. That's probably how yours was originally routed. Pumping gas from a saddle tank to the main tank would be risky if you didn't pay close attention, as it could overflow. That's not how they were plumbed, either, or you'd have yet another valve to switch between the saddle tanks to the pump and then to the main tank.

[Orange Crate]

You can still get the three way valves new.


https://www.amazon.com/Moeller-Fuel-.../dp/B000MTB7QA

[wilkin250r]

My truck had a similar system, and I was told it was factory, not aftermarket.

I've known this truck for years, but I never utilized the saddle tanks myself. But I seem to remember it being a transfer to the main tank, hence the fuel pump, but I could be wrong. I think I was 12 when I first saw it.

But unfortunately I can't help you solve your problem, my saddle tanks were removed years ago, and most of the plumbing with it. The only thing that remains is the valve, the fuel pump, and a few rotted lines going to nowhere...

[SavageC20]

Originally Posted by Steeveedee

The hose from each saddle tank and the main tank are routed to the transfer valve, and one line goes to the fuel pump. On my truck, there were rotten neoprene fuel lines running up over the driveshaft, held up by zip-ties. I converted them to steel lines for the up and over part. I have an electric fuel pump on my truck between the transfer valve and the fuel pump, to defeat vapor lock if it rears its ugly head. That's probably how yours was originally routed. Pumping gas from a saddle tank to the main tank would be risky if you didn't pay close attention, as it could overflow. That's not how they were plumbed, either, or you'd have yet another valve to switch between the saddle tanks to the pump and then to the main tank.

So you have the "out" line on the three way valve going to an electric fuel pump? Does the line go from the electric pump to the main line that runs to the mechanical fuel pump on the side of the block? Does the mechanical fuel pump on the side of the block pull the fuel through the electric one while it is off?

[Steeveedee]

Originally Posted by SavageC20

So you have the "out" line on the three way valve going to an electric fuel pump? Does the line go from the electric pump to the main line that runs to the mechanical fuel pump on the side of the block? Does the mechanical fuel pump on the side of the block pull the fuel through the electric one while it is off?

Yup. Yup. And yup. Never had a problem with this setup (it was like that when I got it) and it has the added benefit of getting enough pressure on the suction side of the mechanical fuel pump to minimize vapor lock. Though I'm thinking that by the time I get the running temperature into a reasonable zone that the vapor lock problem will be gone. it only happened once, anyway.

[SavageC20]

Originally Posted by Steeveedee

Yup. Yup. And yup. Never had a problem with this setup (it was like that when I got it) and it has the added benefit of getting enough pressure on the suction side of the mechanical fuel pump to minimize vapor lock. Though I'm thinking that by the time I get the running temperature into a reasonable zone that the vapor lock problem will be gone. it only happened once, anyway.

Awesome, I was confused on how all of the lines were set up because they were all cut. Now I can finally get around to hooking up these saddle tanks. Thanks for your help.

[Steeveedee]

Originally Posted by SavageC20

Awesome, I was confused on how all of the lines were set up because they were all cut. Now I can finally get around to hooking up these saddle tanks. Thanks for your help.

No problem. The lines going to the transfer valve all go in where the three connectors go, and the engine fuel pump suction line is the one all by itself. On my truck, the handle on the lever is towards the seat for the main tank, it points forward when on the right tank, and to the rear when on the left tank. If you hook it up that way, that is. My truck isn't marked at all by the valve to tell you which position draws from which tank. You can just do what you want, but don't forget, or you will find out the hard way, when that tank runs dry! Since you aren't racing, don't worry if the nipples on the saddle tanks are only 1/4". You won't be pulling that much fuel, even when pulling a 7% grade with a 6000 pound trailer behind you. You might check that your engine fuel pump can pull fuel through that antique fuel pump there before you get too far into it, too.

[jocko]

some refs for saddle tanks

[SavageC20]

Originally Posted by Steeveedee

No problem. The lines going to the transfer valve all go in where the three connectors go, and the engine fuel pump suction line is the one all by itself. On my truck, the handle on the lever is towards the seat for the main tank, it points forward when on the right tank, and to the rear when on the left tank. If you hook it up that way, that is. My truck isn't marked at all by the valve to tell you which position draws from which tank. You can just do what you want, but don't forget, or you will find out the hard way, when that tank runs dry! Since you aren't racing, don't worry if the nipples on the saddle tanks are only 1/4". You won't be pulling that much fuel, even when pulling a 7% grade with a 6000 pound trailer behind you. You might check that your engine fuel pump can pull fuel through that antique fuel pump there before you get too far into it, too.

Mine was hooked up to run off the main tank when the lever on the valve is facing toward the front of the truck. I think the nipples on the saddle tanks are actually male threaded ends. I'll have to figure something out with that but it shouldn't be too hard. I believe my mechanical fuel pump will pull it as I replaced it with the same brand/spec unit (carter) that was originally on there when I got the truck. Good info on the 1/4 inch fuel line.

[SavageC20]

Originally Posted by jocko

some refs for saddle tanks

Thank you, these will be a tremendous help.

[Steeveedee]

Originally Posted by jocko

some refs for saddle tanks

I take it that this would be dealer-installed tanks? I don't have floats or senders on my saddle tanks. That sure would be a useful feature, since I have to calculate how far I can drive and then switch before I run out of gas.

[jocko]

Generally speaking yes, but I believe they could also be owner installed. I haven’t seen many with fuel senders personally, one would just switch the tank when it started to die. I agree, would be nice to have.

[Steeveedee]

Originally Posted by jocko

Generally speaking yes, but I believe they could also be owner installed. I haven’t seen many with fuel senders personally, one would just switch the tank when it started to die. I agree, would be nice to have.

Heh, we borrowed what is now ourtruck from my parents-in-law to take the family on vacation. We were heading up the 1 highway by Carmel when the saddle tank I was using ran dry. The truck started to stumble, and I quick switched tanks. This truck has always had a hard starting issue when hot, and if it had completely died on that part of the road, traffic would have gotten backed up fast! It's one lane each way; a winding road with a hillside on the east and a cliff on the left. My neighbor had a '76 1/2T GMC that he junked out. I should have bought it and removed the two tanks and used that wiring harness and dash so that I had the switches and all. Oh well, opportunities missed.

[SavageC20]

I cleaned up the big grease ball next to that fuel pump and discovered an old Fram fuel filter housing. Definitely going to put this unit back into service. I also found out that the Stewart Warner fuel pump in the pictures is worth some decent coin. That model fuel pump was used on A/C Cobras and GT-40's among other things. If it still works i'll rebuild it.