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Old 06-21-2014, 08:58 AM   #1
G.M.
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Default fuel return line conclusion

After many days of test driving my 39 with a return line after the pump back to the filler neck. The line has a 1lb check valve and a .070 restriction hole after the check valve. Line used was 3/16" OD steel brake line. Driven in temperatures over 90 degrees the car ran perfect, never skipped a beat and could idle without any signs of vapor lock. If the fuel pump temperature gets over 125 degrees the vapor lock starts, at 135 your into VL. When the engine is running with the return line even at idle the pump remains below 115. My car is black and gets real hot in the sun. A 39 has poor fan circulation due to the low location of the crankshaft mounted fan. The air is pushed into the front of the engine with very little or no air over the top of the engine. At driving speeds the air created by forward motion go's through the full surface of the radiator with some air over the top of the engine. Another problem with the 39 is no area at the rear in the firewall area for hot air to escape. As a result everything on or near the rear of the engine gets to over 135 degrees. Insulating fuel lines, raising the pump, heat sinks and other heat transfer method do nothing to reduce heat. The only thing that worked was a high speed computer fan over the pump with a funnel like duct directing air on the pump. Heat sinks eventually get to the same 135 degree temp. The return line keeps the pump cool at any engine speed as long as the engine is running. I had 2 occasions where it didn't start on the first turn of the engine after sitting for a while in the sun and had to turn over 6 or 8 turns and needed to be choked. Then on a 94 degree stop for lunch parked in the sun it wouldn't start after 8 or 10 turns of the engine. I got out and the glass bowl was just about empty, I grabbed the laser thermometer and the pump was 135. I removed the air cleaner and shot some either down the carb and it started and with a few more shots picked up fuel and was running. I checked the pump temperature as soon as it started and the temperature was falling and went right down to 116. I don't think this situation would happen very often with the return line but it can. I just happened to think of a cooling fluid that comes in spray cans for cooling electronic components when looking for over heating problems. This would cool the pump fast and as soon as the temperature drops to in the 120 range the engine will restart. I know the electric pumps work but I just don't like them. G.M.
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Old 06-21-2014, 09:48 AM   #2
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Default Re: fuel return line conclusion

Thanks for the latest report on your return line experience. Very good info which validates your return line solution.
Random thoughts: It seems your few "failure to start" episodes were due to heat soak after shutdown. Return line wouldn't help in this situation. Spray can of coolant is a great idea. Or, maybe just take more time for lunch - eventually the pump has to come down in temp if just sitting longer. Even with the return line, an auxiliary fan (switched on just when stopping for a short time on a hot day) might solve the heat soak problem. Unfortunately, the aux fan looks out of place.
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Old 06-21-2014, 01:06 PM   #3
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Default Re: fuel return line conclusion

What do you think would happen if you took the fuel line and instead of going up the firewall, wrap it around the steering column tube a few times ,( like a still ) then up the firewall. That may be one of the coolest spots in the engine compartment and it would maybe keep it a few degrees cooler before going into the fuel pump..
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Old 06-21-2014, 03:58 PM   #4
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Default Re: fuel return line conclusion

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What do you think would happen if you took the fuel line and instead of going up the firewall, wrap it around the steering column tube a few times ,( like a still ) then up the firewall. That may be one of the coolest spots in the engine compartment and it would maybe keep it a few degrees cooler before going into the fuel pump..
This wouldn't make any difference. I already tried moving the fuel line away from the fire wall, put 1/4" ID rubber hose over it, still no help. Put air conditioning foam insulation over the rubber from down near the frame, over the flex line and right up to the pump, still no help. It's the pump it self that gets heat soaked. I tried every thing from all directions and it comes down to the pump it self. This was after months of trial and elimination. G.M.
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Old 06-21-2014, 04:44 PM   #5
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Default Re: fuel return line conclusion

I agree with the heat soak thing,as when towing our caravan with the 33 out west in 30plus deg C,when you stop for coffee or a leak,when you take off again about 100yds down the road it splutters for a while then smooths out and is OK.
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Old 06-21-2014, 05:32 PM   #6
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What prevented the hard start after a stop was raising the hood while stopped. Worked every time but I don't like doing it, so I use the electric pump as needed.
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Old 06-21-2014, 05:46 PM   #7
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Default Re: fuel return line conclusion

George, you don't like the electric pumps... Here's an idea that you may go for: To overcome the heat soak restart, patch in a hand pump like they sometimes install on Speedsters.
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Old 06-21-2014, 07:03 PM   #8
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Default Re: fuel return line conclusion

I think this is a great idea, wish I thought of it. I'm using a return line regulator on my next project and have modifies the tank for the return line. I never thought of the cooling affect it would have on the carbs. I'm also considering having several 8BA stye fuel pumps rebuilt for the new gas, as the electric pumps seem to be unreliable.
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Old 06-21-2014, 10:35 PM   #9
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I keep a ziplock bag of ice in a cooler for the hot months and put the bag on the pump when I park. Still doesn't help the starter from dragging when it's hot though
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Old 06-22-2014, 12:22 AM   #10
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Default Re: fuel return line conclusion

G.M. You did good. Very good. You tried something that others have only thought about and talked about doing (including me) and tested it in all circumstances that you could and, even though it did not totally solve the vapor lock problem as well as an electric pump does, we all now know what it will and won't do and know way more than we ever knew before about this approach to the vapor lock problem.

Thanks.
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Old 06-22-2014, 09:50 AM   #11
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Originally Posted by G.M. View Post
After many days of test driving my 39 with a return line after the pump back to the filler neck. The line has a 1lb check valve and a .070 restriction hole after the check valve. Line used was 3/16" OD steel brake line. Driven in temperatures over 90 degrees the car ran perfect, never skipped a beat and could idle without any signs of vapor lock. If the fuel pump temperature gets over 125 degrees the vapor lock starts, at 135 your into VL. When the engine is running with the return line even at idle the pump remains below 115. My car is black and gets real hot in the sun. A 39 has poor fan circulation due to the low location of the crankshaft mounted fan. The air is pushed into the front of the engine with very little or no air over the top of the engine. At driving speeds the air created by forward motion go's through the full surface of the radiator with some air over the top of the engine. Another problem with the 39 is no area at the rear in the firewall area for hot air to escape. As a result everything on or near the rear of the engine gets to over 135 degrees. Insulating fuel lines, raising the pump, heat sinks and other heat transfer method do nothing to reduce heat. The only thing that worked was a high speed computer fan over the pump with a funnel like duct directing air on the pump. Heat sinks eventually get to the same 135 degree temp. The return line keeps the pump cool at any engine speed as long as the engine is running. I had 2 occasions where it didn't start on the first turn of the engine after sitting for a while in the sun and had to turn over 6 or 8 turns and needed to be choked. Then on a 94 degree stop for lunch parked in the sun it wouldn't start after 8 or 10 turns of the engine. I got out and the glass bowl was just about empty, I grabbed the laser thermometer and the pump was 135. I removed the air cleaner and shot some either down the carb and it started and with a few more shots picked up fuel and was running. I checked the pump temperature as soon as it started and the temperature was falling and went right down to 116. I don't think this situation would happen very often with the return line but it can. I just happened to think of a cooling fluid that comes in spray cans for cooling electronic components when looking for over heating problems. This would cool the pump fast and as soon as the temperature drops to in the 120 range the engine will restart. I know the electric pumps work but I just don't like them. G.M.
GM i have used this exact type of routing fuel lines and it always worked to stop vapor lock. I it did not work on a flathead it must be a Ford defect.
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Old 06-22-2014, 10:34 AM   #12
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Default Re: fuel return line conclusion

Marv I don't understand your answer. It sounds like you insulated the fuel lines on other make cars and it worked?? The Ford fuel pump is mounted different than other makes. It sits on the engine in the rear where hot air is trapped. Some old Fords are worse than others as far as air circulation at the rear. The pump sits VERY close to the intake manifold which gets over 150 degrees. Aluminum intake manifolds are worse then cast iron ones. The clearance between the bottom of the pump on the aluminum is about 3/8" and the cast iron maybe 3/4". But even without the manifold heat the firewall and everything in the area gets to 135 or higher and stays there. The after shut down raise in temperature of the pump comes from every thing in the area but I would say a lot come off the manifold. I tried a 1" spacer under the pump mounting base raising the pump 1" and an aluminum shield under the pump with several layers of hi tec insulation between the several layers of aluminum which didn't help. Any thing and everything sitting in that area gets hot on hot days. G.M.
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Old 06-22-2014, 11:03 AM   #13
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Default Re: fuel return line conclusion

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GM i have used this exact type of routing fuel lines and it always worked to stop vapor lock. I it did not work on a flathead it must be a Ford defect.
In a way it is a flathead defect because of where the fuel pump is located as G.M. explained but it didn't matter back when the engines were built and not so much before alcohol was added to the gasoline that lowered the boiling point and made vapor lock worse. That was a problem that Ford had no need to consider in his design. I rarely ever had vapor lock when I drove my car in the 60's but it's a chronic problem now. I was loath to modify Old Henry in any way but I got tired of getting out and pouring water on the fuel pump to get going again when vapor locked so put in the electric backup. I use it a lot in the summer driving around town and on road trips.
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Old 06-22-2014, 06:22 PM   #14
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I know the electric pumps work but I just don't like them. G.M.
I'm curious what you don't like about them?
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Old 06-22-2014, 06:36 PM   #15
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Default Re: fuel return line conclusion

I'm glad that George has taken the time to do the research and testing in an attempt to vanquish Vapor Lock, and I understand his dislike of electric fuel pumps however, I have been running an electric (12 volts) fuel pump on our '47 Ford Convertible for almost 15 years, without a problem. I also have an electric (12 volts) fuel pump on our '51 F-1 for around 5 years, with no problems, and no Vapor Lock issues. I recently installed an electric fuel pump (6 volts) in our '39 CS, using an OEM fuel pump (converted by Marv, here on the FordBarn, to be a "pass through") and it has solved the vapor lock problem. I just converted an OEM style fuel pump to use as a "pass through" on our '39 LZ with a (12 volt) electric fuel pump. It works for me.
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Old 06-22-2014, 07:11 PM   #16
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Marv I don't understand your answer. It sounds like you insulated the fuel lines on other make cars and it worked?? The Ford fuel pump is mounted different than other makes. It sits on the engine in the rear where hot air is trapped. Some old Fords are worse than others as far as air circulation at the rear. The pump sits VERY close to the intake manifold which gets over 150 degrees. Aluminum intake manifolds are worse then cast iron ones. The clearance between the bottom of the pump on the aluminum is about 3/8" and the cast iron maybe 3/4". But even without the manifold heat the firewall and everything in the area gets to 135 or higher and stays there. The after shut down raise in temperature of the pump comes from every thing in the area but I would say a lot come off the manifold. I tried a 1" spacer under the pump mounting base raising the pump 1" and an aluminum shield under the pump with several layers of hi tec insulation between the several layers of aluminum which didn't help. Any thing and everything sitting in that area gets hot on hot days. G.M.
The point i was trying to make is that Ford screwed up with that fuel pump location and every vehicle i have done with the bypass method worked fine. I was not disagreeing with your findings. This was being done back in the 50's by an old friend of mine which was quite a mechanic in his day,and a good bit older than i. He was a flathead Ford man.They even had trouble with vapor lock with the old gas when the cars were new and you ran them hard. Marv
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Old 06-23-2014, 07:51 AM   #17
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Default Re: fuel return line conclusion

Marv: Thanks, Where did you but the check valve?
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Old 06-23-2014, 08:15 AM   #18
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Default Re: fuel return line conclusion

The pumps on most other make cars a mounted down near pan so fuel when draining back isn't going to have the syphon effect. This may be why Marv didn't need a check valve. It also don't have to lift as high when restarting. I don't like electric pumps because of the mounting under the car where you can't see it, more connections, pressure which in most cases requires another component, a regulator, and reliability. If a straight switch is used possible gas in the oil and if there is a leak it pumps more fuel. The pump with the return cooled the pump from 135 down to 116 in a few seconds. I don't sit there cranking on the starter when it don't start after a few turns. I will drive it later and do some more temperature tests if I can get it to VL. I have to got to Radio Shack to pick up a transformer for another project and will get a can of the cooling spray, Maybe it's Freon?? Modern cars with electric pumps have return lines eliminating some of the objections I have listed. G.M.
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Old 06-23-2014, 09:29 AM   #19
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Marv: Thanks, Where did you but the check valve?
With a electric fuel pump you would not need a check valve, but with the mechanical pump i would put one next to the carb to keep fuel in it and one just before the fuel pump to keep fuel from returning to the tank . I used a ball valve on the return line to regulate how much fuel by passed. Just trial and error. Leave it as far open as you can and still not run out of fuel on top end.
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Old 06-23-2014, 05:01 PM   #20
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Default Re: fuel return line conclusion

The old "ethyl" gas from the 40's or 50's had a clue in its name, to what was added to the gas.
Its not an entirely new thing or new problem. And cars with carburetors have had return lines from the mechanical pumps or at the carb bowl to the tank for a good while. I like the return idea, and thanks to GM for letting us in on his experiment. I shall use this on my truck. In my opinion I prefer it to the leccy pump. Cost a bunch less, especially compared to a "proper" electric pump installation. With inertia switch and regulator and such.
This is my choice, but can understand those who just go electric.
thanks GM.
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