Vapor Lock

[1937pickup]

Lets have some fun on a topic that has been discussed ad-nausum. There is a discussion going on in the Model A section about a strange problem that people are trying to diagnose.
A member, Old182, posted the following regarding gasoline. He seems to know what he is talking about and have direct knowledge of gasoline blending. This post would seem to say that it is impossible for vapor lock to occur.

The issue of vapor lock has come up several times in this thread. While I suppose it's possible, it's unlikely in this case. Here are a few tidbits of information to chew on: Gasoline is made up of about 200 different hydrocarbons that all boil at different temperatures. In a distillation flask, 10 volume % of most gasolines have boiled under 50 to 70*F and all must finish boiling at or before 437*F to meet ASTM D4814, the spec for gasoline in the U.S. Butanes and pentanes are added to gasolines for "front end" volatility (cold starts); butane boiling at 31*F, pentane at 97*F. From there heavier components are added until the gasoline composition is complete with most gasolines finishing at around 400*F (aviation and racing gasolines way below that). The point here is that you may see gasoline bubbling in a clear filter or fuel line, or you may hear it in the carburetor bowl, but that isn't an indication of vapor lock; it's just the light ends boiling. Once the engine is warm, it will run fine with the mid-range and higher boiling components (even though some light ends remain). No offense meant to those suggesting vapor lock. I don't have any data, but I think to boil off enough fuel to cause vapor lock you would have to see actual sustained fuel temperatures well over 325*F, maybe higher. May be possible. Another $0.02.

Let the comments begin.

[Old Henry]

The part of his "theoretical" analysis that is missing is that the entire spectrum of components in gasoline does not need to boil to create vapor lock. The vaporization of any component will create the air pocket that causes vapor lock even though there may be less volatile components that have not boiled. The air created by those components that do vaporize at lower temperatures pushes the rest of the liquid components out of the way so that all there is left in the fuel pump is vapor which it won't pump.

So much for theory compared to reality.

[ora masters]

old henery could you pm me info on 48 inst gauges none of mine work this car set since 1968 can they be fixed what did you do with yours thanks ora

[ford3]

on a hot day and a flathead v/8 run hard and shut down, raise the hood and look down the carb and watch the fuel being boiled out of the carb, you can even hear it percolate,and it for damn sure the temp at the carb is nowhere near 325 degrees, some times a college degree short circuit common sense, or a total lack of under standing of the ford v/8, books are fine, but you can never beat common sense or experience, so who do you believe the book or an engine that restarts after pouring water on the fuel pump and cooling it down?

[FlatheadTed]

I am with the model A guy , .I would say 10 to 20% of the time its the poor functioning fuel pump the rest is the coil . You can imagine the fuel in the glass bowl turing to vapor , I have never seen it ?,On right hand drive cars the exhausted runs beside the fuel line all the way to the tank .

Quote so who do you believe the book or an engine that restarts after pouring water on the fuel pump and cooling it down? .functioning fuel pump the rest is the coil .


Thats about the time it takes for the coil to cool

[ford3]

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lol, no it takes about 30 mins for the coil to cool down and let the engine restart, it takes about 2 mins for the pump to cool down and engine restart, and it doesnt make any difference what happens to the fuel after it leaves the pump, it matters what happens to the fuel in the fuel line and before the pump, if the fuel line or pump gets hot enough to vaporise the fuel the pump wont pump,, it loses it prime, just like the old hand water pumps, you had to pour water in them to get them primed, fuel pumps pump liguid, not vapors, once the fuel turns to vapor in the pump it will not pick up fuel to pump to the carb, so even if the fuel vaporises in the line to the fuel bowl the fuel being pumped by the pump will still get fuel to the carb, vapor or not, why will a coil quit on a 20 degree day and the fuel pump wony vapor lock? any way im done posting on this subject and im now just going to sit back and read the responses on this subject

[Vic Piano]

I would have to agree that Vapor Lock doesn’t exist... that is; until you experience it for yourself... At that point, it becomes very real, no longer abstract, and the ramifications can be disastrous depending on where and when the previously non-existent Vapor Lock monster rears its ugly head... Go ahead; ask me how I know...

[Blu Dice]

No comments on todays gas? I think it's more likely to happen with today's gas since there is more "corn" in it - comments?

[DICK SPADARO]

I have no idea where the 1937 pu got his information but I think it should be reviewed again because it doesnt appear to be accurate on the explanation of vapor lock. Remember we are in the New Liberal America fuel agenda era, the good old days are gone! Fuel you are using today is supplemented with 10% ethanol as a filler to reduce emissions, if station fuel is regulated to 15%, kiss your old car good bye. The problem with ethanol is the low vaporization temperature of the liquid. The vapor to liquid ratio becomes important because the ability for the fuel to vaporize is controlled by the volume of fuel, temperature of fuel and the air pressure at that time. Think about it, you are putting a small amount of fuel in confined area like a steel fuel line. This small volume will produce a scenario to cause the fuel to percolate at lower temperature closer to the boiling point of the filler ethanol. Ethanol boils at around 78*C which is about 172*F so that doesnt take much to figure that if your engine coolant is running at 180*F your components are also pretty close to that temperature, especially if you throw in ambient air temperature for a heat sink. The hotter the day the more change that your fuel boils, its not the gasoline part its the additive ethanol turning into a gaseous state.

So if your car is hard to start hot or has stumbling issue when driving its most likely that the fuel is close to a percolation point and you need to address the air flow under the hood , the fuel line routing or simply place an additive in the fuel to raise the boiling point. There is no set answer other than using nonethanol fuels and even they can percolate but at a higher temp.

[Old Henry]

Originally Posted by Blu Dice

No comments on todays gas? I think it's more likely to happen with today's gas since there is more "corn" in it - comments?

Don't know much about "corn" but I do know that vapor lock is a whole lot bigger problem for me now than it was when I drove this same car and engine in high school in the 60's. I can only conclude that it must have something to do with the difference in the way gasoline is formulated now compared to then.

[Old Henry]

Originally Posted by DICK SPADARO

So if your car is hard to start hot or has stumbling issue when driving its most likely that the fuel is close to a percolation point and you need to address the air flow under the hood , the fuel line routing or simply place an additive in the fuel to raise the boiling point. There is no set answer other than using non-ethanol fuels and even they can percolate but at a higher temp.

A lot of good ideas. In addition, I found the simplest and most reliable solution was to install a backup electric fuel pump back by the gas tank to turn on when the mechanical pump vapor locks. That used to be just intermittently in the summer and at high altitudes. Now it is almost constant under those conditions.

[ford3]

Guys, pay attention to what dick said, hes one of few real ford flathead gurus

[1937pickup]

Dick Spardo-I copied the information from a post on the Model A site-now having said that-the post says that some of the additives in gas will boil at a very low point. Others boil at a higher temp. The parts that boil at a higher point are a larger portion of the fuel than those that boil at a low temp. One boils a 31 degrees F, one other at 97 degrees-why then do cars ever run if parts of the fuel are boiling at such low temps? I guess I have been lucky and not experienced vapor lock. For me it like ghosts-you don't believe in them until you see one for yourself.

[Old Henry]

Originally Posted by 1937pickup

Dick, . . . One boils a 31 degrees F, one other at 97 degrees-why then do cars ever run if parts of the fuel are boiling at such low temps?

I ain't no Dick but I'll take a stab at it.
The components of gasoline that "boil" at room temperature are the ones that we smell. In other words, the "boiling" is more "evaporating" than real boiling. That is why gasoline is so aromatic - because some components of it evaporate very quickly, i.e. turn from their liquid form into vapor, even at low temperatures. It's the ones that take a bit more heat to "boil" that create enough vapor to lock up the fuel pump.

[BUBBAS IGNITION]

AND you know that a fuel guy will always blame the ignition 95% of the time , AND the ignition guy will always blame the fuel system 95% of the time .....rbg :>)

So i always say : Its more than likely "vapor lock"....

Good discussion guys with some very realistic thinking in regards to fuel etc....

[JT FORD]

I never had much trouble with vapor lock until a year ago when it was very hot around here. I had trouble with the ethanol. I stopped using it
all together, went to straight gasoline and had no more trouble. By the way blaming it on the coil don't work with a 8BA motor........

[rotorwrench]

I don't know if they still have cold weather blends in some areas or not but they used to. During cold weather months the blending was heavier toward the cheaper component chemicals than the more expensive ones since the colder climate would allow them to stay in fluid state without too many customer complaints. If you have winter blend fuel and the weather turns warm, you can have all sorts of trouble with the lower vapor pressure components. Vapor lock is a real problem but that doesn't mean it is the only problem that might be incountered either.

Avgas is pretty expensive stuff but that is due to limits set by federal standards on the vapor pressure of the component chemicals. You can't afford to have vapor pressure problems when operating an airplane and your altitude can be much higher than the cars will ever see unless they sprout wings.

[FlatheadTed]

This is just my 2 cents for the sake of a discussion ,, The hottest part of any fuel system would surely be the pump, and the low pressure part ,So if you have a glass bowl then I would think you should see vapor in there, On the out put side its under pressure so Unlikely there . Would vapor lock exist If you have a correct working pump ? ,How many pumps get set up as the AC specs with the input vacuum and out put pressures set ,and the CFM tested ,Some people run electric pumps to prime after sitting and to solve vapor lock . A customer of mine removed a 41b electric pump this week on my suggestion due to flooding because it was overcoming the needle valve , Picture added .

[FlatheadTed]

More pictures . I always go back to Ford who Tested there cars in the desert.

[FlatheadTed]

here is a distributor that came in for problem solving because of vapor lock .

[Bluebell]

As a liquid turn to a gas it expands dramatically, but the amount that would cause vapour lock would never be seen at the sight glass. It only needs enough to effect one valve.
A flathead fuel pump (from memory) is supposed to deliver 2 1/2 to 3 1/2 lb of delivery pressure. This pressure is developed SOLELY by the SPRING.
A temperature rise that causes a coil to fail could not be given a (specified) time to recover except to that specific vehicle in that particular set of conditions. What I mean by that is
The coil may never work again, or it could fire the plugs the very next time the button is pushed. every thing else effects the voltage it has to reach to fire.

[FlatheadTed]

Interesting point Blue bell but ,I say vapor in the valve = vapor in the site glass . What spring are we talking about ?

[1937pickup]

Flathead Ted-is that a primer on the fuel pump.

[FlatheadTed]

Yes it is I use this if the car sits for more than 4 weeks .This early pump is marginal because the valve seats have never been replaced ,it should prime in about 30 seconds .

Originally Posted by pickup

Flathead Ted-is that a primer on the fuel pump.

[Bluebell]

The big spring under the diaphragm.

Bluebell from Tga. in the BOP.

[Old Henry]

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Originally Posted by FlatheadTed

. . . if you have a glass bowl then I would think you should see vapor in there,

In all of the vapor lock that shut me down the bowl was always full to the top.

Originally Posted by FlatheadTed

. . . Would vapor lock exist If you have a correct working pump ?

Yes. I've had it with brand new perfectly working pumps.

Originally Posted by FlatheadTed

. . . Some people run electric pumps to prime after sitting and to solve vapor lock .

That's what I did.

Originally Posted by FlatheadTed

I always go back to Ford who Tested there cars in the desert.

But they didn't test them with the kind of gasoline we have to run in them today.

[G.M.]

You have to live where it really gets hot to understand vapor lock. I have seen small bubbles form and raise to the top in the glass bowl. These come from the heat off the metal cup and nut that holds the bowl on. Engines with an aluminum intake manifold get much hotter. Some year cars get much hotter at the rear of the engine due to lack of air flow and no where for the 135 plus degree air to excape. G.M.

[deuce_roadster]

Am I missing something here? This originally came from the Model A section? How does a Model A ever get vapor lock when it doesn't have a fuel pump?? I thought a fuel pump was required for vapor lock to occur!!!
All the discussion seemed to be appropriate for the V8 section but I would like to know how a gravity feed system can have vapor lock.

I am old, I could have missed an important post.

[FlatheadTed]

GM ,Henry Yes the gas blend . I don't live in a hot place thats my stumbling block .I think the only way is to do some testing .

[Tom Walker]

Originally Posted by deuce_roadster

Am I missing something here? This originally came from the Model A section? How does a Model A ever get vapor lock when it doesn't have a fuel pump?? I thought a fuel pump was required for vapor lock to occur!!!
All the discussion seemed to be appropriate for the V8 section but I would like to know how a gravity feed system can have vapor lock.

I am old, I could have missed an important post.

I believe the problem in the Model A is fuel boiling in the float chamber. Intake and exhaust is on the same side and the carb gets heated by the exhaust manifold. It can be cured wthe heat shield.

[G.M.]

You need a laser pointed thermometer to pin point the problem.This new gas boils at low temperatures. G.M.

[FlatheadTed]

Your pump needs to be capable of pumping air ,If you fit a fresh pump on how does the fuel get pumped up from the tank ,its first sucking air , So air or gas whats the difference ? How do they compress gas into tanks ,they use a diaphragm pump at least for the lower pressure ones .
Tom ,There has been Carburetters made as vaporizers .?

[1937pickup]

Tom Walker-here is a link to the discussion on the Model A site.
http://fordbarn.com/forum/showthread.php?t=95803