Fuel line size
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Tuned
Joined: Feb 2002
Posts: 441
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From: Vicksburg, MS
Fuel line size
I have a '78 F250 2wd LB with dual tanks. I just relined the inside of my rear tank, and I did the side tank about a year ago. I just bypassed the rear tank and ran a rubber line to the mech fuel pump in the meantime.
I'm now ready to reinstall the rear tank, a new selector valve, and an electric fuel pump. I plan to keep the existing steel lines. Unless I am mistaken, all the stock components were 5/16", right?
The new steel, pre-bent lines I see are 3/8". My question is what is the point of increasing the line diameter unless everything in the system is 3/8"? The sending unit lines are going to 5/16", and the selector valve is 5/16". Is it wise to have inconsistent sizing in the lines?
I'm now ready to reinstall the rear tank, a new selector valve, and an electric fuel pump. I plan to keep the existing steel lines. Unless I am mistaken, all the stock components were 5/16", right?
The new steel, pre-bent lines I see are 3/8". My question is what is the point of increasing the line diameter unless everything in the system is 3/8"? The sending unit lines are going to 5/16", and the selector valve is 5/16". Is it wise to have inconsistent sizing in the lines?
Cargo Master
Joined: Mar 2002
Posts: 3,132
Likes: 218
From: W (BY GOD) V
3/8" is normally for HI-PO or high demand engines. Intermingling is a waste of money (IMO) and will be harder to service in the future.
https://www.inlinetube.com/brake--fuel-lines
https://www.inlinetube.com/brake--fuel-lines
Cargo Master
Joined: Nov 2011
Posts: 3,354
Likes: 48
From: Great American SouthWest
On my trucks, in stock form, everything behind the fuel pump was 3/8 and everything in front was 5/16. Don't know why.
Only reason I can think of is that it increases the flow speed and/or pressure to prevent vapor lock.
Only reason I can think of is that it increases the flow speed and/or pressure to prevent vapor lock.
Postmaster
Joined: Nov 2011
Posts: 2,553
Likes: 10
My truck (F250/400) is 3/8" behind the pump and 5/16" from pump to carb. I understand some trucks were built with 5/16" behind the pump.
After the fuel is pressurized by the pump, line size, restriction and tendency to vapor lock is not much issue. 5/16" is plenty.
Before the pump, different story. The pump is sucking the fuel and pressure is low. Restriction there can eaisly cause vapor lock. A bigger fuel line helps minimize restriction.
One thing to watch out for are re-pop fuel senders. I could not find one for the rear tank that was 3/8" to match my lines. I had to adapt a 5/16" pickup.
After the fuel is pressurized by the pump, line size, restriction and tendency to vapor lock is not much issue. 5/16" is plenty.
Before the pump, different story. The pump is sucking the fuel and pressure is low. Restriction there can eaisly cause vapor lock. A bigger fuel line helps minimize restriction.
One thing to watch out for are re-pop fuel senders. I could not find one for the rear tank that was 3/8" to match my lines. I had to adapt a 5/16" pickup.
Thread Starter
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Tuned
Joined: Feb 2002
Posts: 441
Likes: 0
From: Vicksburg, MS
So it seems that my hard lines from tanks to pump is 3/8" after all. My original pickup tubes were 3/8", but the new ones are 5/16". My new valve selector is somewhere in between.
Based on some old threads here, I planned on mounting the electric pump near the selector valve. Now, I have to do something where the mech pump was.
1. Bridge the gap from the 3/8 line to the 5/16 pump to carb line with hose.
2. Replace the 5/16 line with 3/8 hose
3. Replace the 5/16 line with a new 3/8 line and bridge the gap with hose.
Based on some old threads here, I planned on mounting the electric pump near the selector valve. Now, I have to do something where the mech pump was.
1. Bridge the gap from the 3/8 line to the 5/16 pump to carb line with hose.
2. Replace the 5/16 line with 3/8 hose
3. Replace the 5/16 line with a new 3/8 line and bridge the gap with hose.
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Cargo Master
Joined: Nov 2011
Posts: 3,354
Likes: 48
From: Great American SouthWest
So it seems that my hard lines from tanks to pump is 3/8" after all. My original pickup tubes were 3/8", but the new ones are 5/16". My new valve selector is somewhere in between.
Based on some old threads here, I planned on mounting the electric pump near the selector valve. Now, I have to do something where the mech pump was.
1. Bridge the gap from the 3/8 line to the 5/16 pump to carb line with hose.
2. Replace the 5/16 line with 3/8 hose
3. Replace the 5/16 line with a new 3/8 line and bridge the gap with hose.
Based on some old threads here, I planned on mounting the electric pump near the selector valve. Now, I have to do something where the mech pump was.
1. Bridge the gap from the 3/8 line to the 5/16 pump to carb line with hose.
2. Replace the 5/16 line with 3/8 hose
3. Replace the 5/16 line with a new 3/8 line and bridge the gap with hose.
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Ford Parts Specialist
Joined: Nov 2006
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From: Simi Valley, CA
1975/79 F100/350.
The fuel tank selector switch located in the heater control panel switches the tanks and the dash fuel gauge from one tank to the other.
Cargo Master
Joined: Mar 2002
Posts: 3,132
Likes: 218
From: W (BY GOD) V
My truck (F250/400) is 3/8" behind the pump and 5/16" from pump to carb. I understand some trucks were built with 5/16" behind the pump.
After the fuel is pressurized by the pump, line size, restriction and tendency to vapor lock is not much issue. 5/16" is plenty.
Before the pump, different story. The pump is sucking the fuel and pressure is low. Restriction there can eaisly cause vapor lock. A bigger fuel line helps minimize restriction.
One thing to watch out for are re-pop fuel senders. I could not find one for the rear tank that was 3/8" to match my lines. I had to adapt a 5/16" pickup.
THANX!
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