Old wives tales?

Fact or fiction...
Flathead Fords or any old tractor could VAPOR LOCK ??????????
Explain what is Vapor Lock.
In the 50's, Dad was putting clothespins on the fuel line
on the ole' flathead Ford to prevent vapor lock.
Is modern gasoline different than 50's era gas, in that respect?

Vapor lock is caused when the gasoline gets so hot that it boils or vaporizes in the lines and the carburetor. Since the fuel pump cannot pump vapor and the carburetor starts to run dry the engine dies. Many tricks of the trade were tried to eliminate the problem. The best solution on a hot day was to cool the fuel lines and fuel pump with cold water or wet rags or just sit back with the hood up and wait for everything to cool down. Vapor lock is now virtually eliminated by the use of fuel injection whereby fuel is delivered and distributed to the engine under pressure which insures that the gasoline will remain a liquid.

Vapor lock is a void in the fuel line that used to occur from heat in the engine compartment in most cases,the old remedy of putting a clothes pin or multiple clothes pins on the fuel line would lower the temp. to not allow gas to vaporize in the line,insulating the line would do the same thing,today's systems for the most part use electric fuel pumps and fuel injection so there is constant pressure in the lines and vapor lock doesn't occur. Fuel line routing was also a problem that added to vapor lock,higher humps in the line tended to make a pocket that was prone to locking or making a void in the fuel delivery.Also the pumps back in the day only delivery fuel in the five PSI range at the time.

Haven't got this one running yet to see if I might have to replace these.

Vapor lock happens when the fuel boils inside the line creating pockets of gas vapor instead of flowing liquid.

On a tractor, the convenient place for the tank was above the engine, and the line routed down beside the manifold would sometimes get too close to the heat and instead of liquid coming down, boiling fuel will send expanding pockets of vapor back up the line, pushing the fuel back to the tank instead of down to the carb.

On the old cars, the problem was multiplied by the fuel pump being at the front, which draws gas up from the tank. Liquid under even a slight vacuum will boil at a lower temperature, so as the pump creates vacuum, the gas is even more prone to boil both inside the pump and in the line.

Add to that the forward inertia of the vehicle accelerating, or going up hill, or both, which creates more vacuum on the fuel stream just as the demand for fuel is the highest!

As for clothes pins in the fuel line... Never understood that one. The problem is ahead of the pump, not in the line to the carb unless it is somehow routed too close to the exhaust heat, which would have been possible, but I still don't see clothes pins being a solution unless they were holding insulation around the line.

As far as fuel changing, no. It's the delivery system. High pressure pump in the tank pushing the fuel under pressure all the way to the injectors has no chance to boil in the lines.

Ever get a air bubble in a siphon hose and the flow stopped. Ever run a diesel out of fuel and then have to bleed the air out the system to get it to start.
Both of these are vapor lock.

What happens in a gas system is the fuel turns from a liquid to a vapor on the suction side of the pump and the pump looses prime. Since parts of gasoline start to vaporize at 85 degrees this can happen at normal engine temperatures.

Most pumps are not good a pumping air. They rely on siphon action to work effectively and a air bubble in the system kills them when you are relying on a steady flow.

On the old tractors with a gravity flow system it is technical impossible for the system to vapor lock because there is no pump and there is no siphon action in play. What happens here is the fuel turns to a vapor and vapor flow uphill while liquid flows down hill this causes a traffic jam in the fuel line disrupting fuel flow to the carburetor.

Yep, as the others have said, vapor lock is real. I suspect the flathead V-8's would vapor lock. I know for a fact the Y-block engines could do it even on a comfortable day, 272,292,312 V-8's. Dad had a '56 F-350 single rear wheel pickup with 292 & 4-speed. It could carry as much as any 3/4 ton Chevy, plus tow our Heider augerwagon with 5000# of ground hog feed and still pass the Chevy about a mile north of town. Problem was the exhaust cross over pipe from left exh manifold to right side manifold passed within less than a half inch of the fuel line between the fuel pump and carb. Slowing down to turn onto our road was enough to vapor lock the engine. On lucky days there would be accumulated rain water in the ditch to trickle on the fuel line, fuel pump, maybe even the carb. While cooling the beast off, the Chevy would drive by slowly, sometimes stop and ask if we needed help. Nope, just time with the hood up. A full dual exhaust would have ended the problem. When we cleaned the shop out when we moved I found 4-5 nearly new carbs and fuel pumps, even a couple wraps of aluminum foil would have helped.
About 8-10 years later I'm driving our township road depot's '59 F-750 spreader truck in the next township west, as the day got hotter the vapor lock on it got worse, a low gear and high rpm were the only cure that day. Pop the hood and the engine looked exactly like Dad's F-350.
My farm tractor experience is mostly with FARMALL'S, M,H, 450, never had one vapor lock, now a 2 cyl Deere I can see vapor locking, neighbor's WD-45 Allis, D-17 & D-19 never vapor locked either. Thing the Allis's and FARMALL'S had in common, gas tank away from engine heat, carb in air blast from fan out in the open.
My '78 F-150 with 300-6 had exactly the OPPOSITE problem. I picked my Buddy up one Saturday morning in January, was about 10-12 Below, drove about 60-70 miles and my buddy had to have me stop, relieve his bladder and get another cup of coffee. Temp guage showed truck was up to temp, pulled up to stop sign on exit ramp and the thermostatic coil spring has the fast idle cam activated and truck idling 2000 rpm, about 50 mph. A vinyl home-made winterfront, a cold air shroud around the carb and automatic choke, and the automatic choke would actually turn off. I also converted to a manual choke. Think I got about 6-7 mpg on that trip that morning, not my usual 12-14. My '74 Chevy LUV by Izuzu had a manual choke, but was a rotting rusting piece of junk otherwise. And it never idled fast like that. But in order to start at 10 below I had to hook up battery charger AND plug in the block heater and starting was still "Iffy" below zero. Had to drive the first mile in low gear, the manual 4 spd trans wouldn't shift, UNTIL I put IH Hy-Tran in it.

We used to wrap aluminum foil loosely around the fuel line, leaving wide flat fins on the foil. I can't remember the year model of the vehicle, but I know it was a Ford six cylinder engine with a loop in the fuel line to the carb. When I worked in a service station in the sixties, it was real common to "cure" those Ford sixes with about a foot of aluminum foil.

When I was in high school, I had a '36 Ford that would vapor lock. In fact, after market fuel pumps had a valve like a radiator drain valve on the side that was supposed to overcome the vapor lock when it was opened. It didn't always work.

So, yes, flathead Fords would vapor lock.

Old Ford schoolbus with flathead V8 on the way to the State Fair. Going uphill, engine quit. Somebody came by and stopped. said they'd send help. Tow truck pulled up a while later. Driver came up with a big pour can of cold water. Didn't even ask. Just went up to the side of the engine and poured cold water on the fuel pump. Engine started right up and never gave another lick of trouble. Wisconsin air cooled V4s had the same problem but it usually happened when shut down hot. Wouldn't want to start right away.

Fuel pump in the tank pretty much eliminates vapor lock. As for gasoline, it is reformulated in the summer for lower vapor pressure, which reduces the likelihood of vapor lock in those few vehicles that are still subject to it. (The gas is reformulated mainly to reduce evaporative emissions, rather than to prevent vapor lock.)

It is still possible to get vapor lock in modern vehicles, but much less likely. Fuel under pressure boils at a higher temperature than fuel at or below atmospheric pressure. And most modern vehicles have return lines that allow excess fuel to be pumped through the fuel system and returned to the tank for cooler fuel.

On a hot summer day, my '64 VW bug would vapor-lock while parked. I carried a bottle of water to pour on the fuel pump for this occasion.

Anything with carburetor can vapor lock, as can anything without tank mounted fuel pump if fuel line gets hot.

Wisconsin engines - I've eaten many hay maker meals with the baler engine running outside while we ate. They started nice when cold - not so nice when hot.

Learned a lot of new cuss words as a young feller, when the Wisconsin motor would konk out on a 100 degree day, on the old New Holland canvas baler.
Also didn't think a human could throw a crank handle that far, either.

It is my understanding that Chrysler s fix was the third line on some or their fuel filters. The extra line goes back to the tank as a return line(top of the tank) I don t know how it would work on a gravity system.

Never had a problem on the 2 cylinder Deeres nor the H Farmal or 2N Ford. I have understood that a lot of that problem was rerouted fuel lines and not factory fuel lines.

The 37-38-39 Fords used to have hood side panels that came off with loosening a couple
thumb screws.. This released a lot of the heat. My dad said a trick was to add some kerosene to the gas to lower the vapor pressure. Old Ford flathead V8s used to make a lot of heat because the exhaust ran through the water jacket from the valves to the exhaust manifolds. Sixes didn't do that. Cadillac flathead V8s had the exhaust manifolds on top and the exhausts went directly from the valves to the manifold. Some racing guys created this system for the Fords by reworking the camshaft so the intake came from the former exhaust ports and the exhaust went out the top like a Cadillac. Ford had prototype engines built to help with this problem, but they didn't go into production because they probably cost ten bucks more to build.
By the way, the Lincoln V8 which inspired the Ford V8 had the exhaust manifolds on the top of the Vee. Might have run cooler, but being close to the carb, may still have vapor locked.
Old Lincoln V8

Dad had a hand crank on a Wisconsin stick on the motor shaft, That crank was spinning around and shaking the motor. I thought the thing was going to explode. Dad finally got it shut off. Stan

(quoted from post at 04:14:39 05/06/20) Fact or fiction...
Flathead Fords or any old tractor could VAPOR LOCK ??????????
Explain what is Vapor Lock.
In the 50's, Dad was putting clothespins on the fuel line
on the ole' flathead Ford to prevent vapor lock.
Is modern gasoline different than 50's era gas, in that respect?

Click to expand...

We had a 40s browning truck crane and in the summer you never peed before going down the road with it. Urine would do the trick to cool the gaslines

Had an 801 Ford that never did run right on ethanol blends unless you wrapped the gas line in mud when cultivating tobacco.

37 Chief - I worked one winter on a bridge construction project. They had an ancient welder on a trailer that was powered by a Wisconsin engine. The carpenters welded the piling splices and ran the welder. It would almost but not quite start one cold morning, and the two carpenters cranked until they were wore out, with the foreman making fun of them the whole time. Finally, every man on the job had tried to start it and had failed, with the foreman still running his mouth. He was a strong man, and he was gonna demonstrate how to start that thing. I'll have to admit, he could whip that engine over, and it wanted to run, but not on its own. What we (and he) didn't realize was that he was pulling the crank off of the crankshaft as he cranked, and when it did come off, the crank end flew around and hit him on the chin. He fell like an oak tree and just laid there. We all thought it was the funniest thing we'd ever seen, until it dawned on us that we'd better check his pulse. He was still ticking, so we drug him by the heels over by the fire barrel and he slowly came to. Every morning thereafter, we'd holler up to Bill the foreman to come down and show us how to start that welder.

Good afternoon! Several have explained what vapor-lock is. Various cars of the 1940s and 1950s were subject to this. I believe the flathead Fords were especially bad because the fuel pump was on top (hottest part) of the engine. Those engines ran pretty hot anyway, since the exhaust valves were near the center of the engine, with exhaust passages through the block to the outer sides of the engine. A lot of exhaust heat went into the block due to the long passageways. That's my opinion...