For vapor lock nonbelievers

[steve s]

Here are some photos that may clarify the vapor lock issue. These were taken while on my knees looking up into the top of my sediment bowl. As I watched, a vapor bubble would grow until it covered the entire screen surface, burp on out the fuel line, and then the process repeat over and over. The first series has the screen in place. The shiny vapor bubble can be seen to grow until it covers the entire underside of the screen surface. The growing bubble lolls off to one side because the bowl is not perfectly level. The fourth (and blurriest--sorry) photo shows the maximum bubble size. Shortly after it gets to this state, the whole bubble blurps out of the bowl outlet and the process repeats endlessly. Each cycle takes a minute or so. The second set of two are without the screen. The two photos without the screen show the inlet with no bubble and then with the nascent bubble just beginning to grow and dance in the hole. Eventually, this would grow and fill the top of the bowl, and blurp on through. The screen didn't seem to make any difference.


This was a fascinating and amazing phenomenon, but very easy to not notice--you can be standing right there watching your motor run and not see it until its pointed out. I observed it many times. The photos were taken on a warm but not real hot Michigan summer day with the motor warmed up and idling but not just driven. I apologize for marginal quality of some photos, but the glass reflections were a challenge. Click twice on the "thumbnail" photos to get a better view.)

The photos show beyond doubt that vaporization does occur. That bubble is vaporized gasoline; there's way too much of it to be air. In this situation, there was vapor, but no actual “lock”. Gasoline seemed to flow sufficiently around the growing bubble, and, amazingly, the idling motor barely hiccupped when the bubble passed. However, it is easy to imagine how under actual running conditions, e.g., after a hard pull, hood closed, and hot day, this sort of thing could occur up and down the fuel line and in the carb, eventually overwhelming the poor motor’s ability to cope.

The vaporization seen in the photos should not be a surprise. Gasoline is a mixture of chemicals that has an initial boiling point around 100 degrees F that gradually rises to around 400 F as the lighter fractions are boiled off. It doesn’t take a very warm day or a motor that is overheating to get the engine compartment up to 100 F. So, why doesn’t everyone have the problem? It is somewhat of a puzzle because there is so much variation, even among members of the same club. Here are some of my thoughts.

Bubble formation is a notoriously non-equilibrium process that can be very sensitive to the nature of the contacting surface and to flow turbulence to get it started, so some individual variation is expected. So-called superheating can result in the unpredictable, sudden emergence of a large bubble that could produce a blockage. Not to pick a fight or anything—but in my experience, fuel filters are particular “occasions of sin” in this regard, to borrow a phrase from the Church: They are not intrinsically evil but they do sort of invite trouble as sites to either initiate vaporization or trap a bolus of vapor. I am also including a picture of various fuel filters I have experimented with, all of which have caused some degree of trouble for me. The clear plastic, inline filter was the most interesting: I could watch it fill up with vapor, after which the engine would stall.

The exact composition and boiling point of gasoline vary by geographical region and season. This may be why vapor lock is not more common down south, where they know it's going to be hot and the gasoline has been formulated accordingly. Further, the big problem with incorporating ethanol into gasoline (beyond dissolving rubber parts) was that it forms a highly “non-ideal” solution with an anomalously high vapor pressure (Raoult’s Law does not apply). When the government mandated incorporation of ethanol, the petroleum companies were challenged to compensate for this lowering of the boiling point by changing other ingredients.

Many other possible vapor lock contributors have been implicated or sworn by or at: presence or absence of engine pans, painted vs. shiny carburetors, fuel filters, bent vs. straighter fuel lines, insulated fuel lines. Although each of these has its fierce partisans, as far as I know, none are definitive. Certainly, none of these are relevant to what is seen in my photos; this vaporization starts as soon as the fuel enters the engine compartment. Many people have advocated a variety of fuel additives; my only experience in that regard is that I saw exactly the same vaporization in the sediment bowl after mixing two quarts of diesel fuel in my tank. Many assume that it’s an engine overheating problem. Again, not in this case; my engine compartment did not feel particularly hot and the temperature gauge shows my motor at a steady 165 F (thermostatted).

Actually, the Model A vapor lock controversy sort of reminds me of the women’s PMS issue: women who don’t personally have the problem are often convinced that those who do are either faking it or have other major competency issues.

Steve Schullery
Kalamazoo

[Ron/IA]

Steve - Well written article. But, I am one of those "non-belivers" of vapor lock in a Model A fuel system. But, I must also say I am no chemical/fuel expert in any way, and I cannot prove my belief.

What I see in your photos is vapor being generated, not being boiled from the gasoline. You can take most liquids, put them in a jar or glass, swirl them to make a whirlpool, and it will generate bubbles in the liquid. I think the swirling action through the sediment bowl is generating the vapor. (EDIT) I also think that vibration can generate bubbles too. I have seen the clear enclose gas filters vibrating from the engine and bubbles inside; then grab the filter to lessen the vibration, and the bubbles quit.

Of course, this is just my theory and I have no way of proving it. Also, I would be intersted in others with more knowledge than I would have to asy about this. - Ron/IA

[Paul from Maine]

Just to eliminate the question of venting, can you repeat the same experiment with the gas cap off? If you get the same results, I would say you proved your point. I am just curious, not trying to start an argument. I've never had vapor lock with my A or T's so know nothing about it, but am intrigued by the thread.

[steve s]

Originally Posted by Ron/IA

...

What I see in your photos is vapor being generated, not being boiled from the gasoline. You can take most liquids, put them in a jar or glass, swirl them to make a whirlpool, and it will generate bubbles in the liquid. I think the swirling action through the sediment bowl is generating the vapor.
... - Ron/IA

Ron,

There are two possible sources of the swirling bubbles you mention, neither or which apply here. One would be entrained air from above the liquid swept down into the liquid by the turbulence; there is no such air reservoir in the sediment bowl. The other could be air dissolved in the liquid that comes out of solution as gas bubbles; this would occur throughout the liquid, which is not the case here.

Also, because there's no sign of bubbles being formed down in the sediment bowl, technically, the liquid there is not boiling. What is happening is very rapid vaporization at the surface of the very first bubble that has formed. Three factors prevent the whole container of liquid from vaporizing: First, once the most volatile components evaporate, the boiling point goes up, or vapor pressure or rate of evaporation goes down. Second, the act of vaporization cools the remaining liquid. Third, heat flow takes time, there is a steady influx of "cool" gasoline.

Hope this helps.

Steve

[Kevin in NJ]

When looking at the pictures keep in mind....

The center hole is the side coming from the fuel tank.
The square hole at the front is going to the carb.

[steve s]

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Originally Posted by Paul from Maine

Just to eliminate the question of venting, can you repeat the same experiment with the gas cap off? If you get the same results, I would say you proved your point. I am just curious, not trying to start an argument. I've never had vapor lock with my A or T's so know nothing about it, but am intrigued by the thread.

Paul,

I have not done the gas cap experiment you suggest. I can't imagine how it could help. My gas cap works just fine: I can drive hundreds of miles at high speed without the carb being starved for gas.

There is already plenty of air over the gasoline in the tank. It is not somehow swimming down through the gasoline to accumulate in the sediment bowl. Letting air have even better access to the gas tank wouldn't make any difference, I'm sure.

Remember, I also watched that clear inline filter fill up with vapor. That's a lot of volume--way more than possible by dissolved or somehow entrapped surface air.

Hope this helps.

Steve

[steve s]

Originally Posted by Kevin in NJ

When looking at the pictures keep in mind....

The center hole is the side coming from the fuel tank.
The square hole at the front is going to the carb.

Kevin,

I have kept that in mind. That is why I showed the picture without the screen where you can see the bubble starting to grow in the center, inlet. Because the bowl was not perfectly level, the growing bubble lolled over to the high side, which was the exit side and sort of makes it look like it might actually be forming there.

Here is another picture that might help you see the bubble coming from the center, with the screen. Unfortunately, it's not well focused and there's a glass reflection right in front of the center hole bubble. But, I think if you look closely you can see what I'm talking about.

Steve

[MikeK]

Nice photos, Steve S. With modern gasoline there will likely always be vapor bubbles in a non-pressurized single tube feed system, filter or not.

As you have stated, addition of ethanol will increase the vaporization potential of a non Raoult gasoline solution, but I place much more of the blame on modern refinery practice. In Henry's day oil was fractionally distilled, but the residuals were not cat cracked as they are today. Modern practice gives us a mix with a much higher vaporization potential. Nobody complains when their car starts at -10F. Try that with 1929 gas! The big culprit is fractions that have less commercial market than the volume produced. Dump as much in the gas mix as is tolerable to the general market (not us!). Butane, a gas at atmospheric pressure and room temperature, is not as saleable as methane or propane, and you get a lot of it from a cat cracker. It gets stored and blended into the gasoline, as much as is area tolerable. That's where I would point the big finger. Yes, ethanol is a lousy add to the blend, but not the major vapor pressure culprit.

As your pictures illustrate, vaporization will occur at any point of slightest pressure variance. The only real fix for a gravity feed system that I can see would be an ugly one. There needs to be a larger fuel line and a small vapor return line to the tank. Reminds me of the new bathroom my neighbor put in. The sink would fill to the top, then burp and drain. The tub drained like a turtle. He ran the new drain line with no vent stack connection! The fix was to tear into the wall again and run an additional stack.

[Bob A.]

Well written Steve, but you’re going to have to do better. All I see is an air bubble which will be displaced by the fuel tank vent or carburetor vent. You did state that the car did not stall out. I'm still a believer that vapor lock can't happen in a gravity feed fuel system. I run two Harley Davidson motor cycles with gravity feed fuel system (48 years) and two model A Fords and never had a problem. These vehicles were all caught in well above 95* weather in bumper to bumper traffic for miles at a time.The bikes get so hot that the family jewels get roasted.
I use regular gas with 10% Pooh Pooh. If I could run something cheaper per gallon I would. When this "Vapor Lock" syndrome occurs in my vehicles then I would be a believer but I know it ain't going to happen because it's Bull Dung.

[James Rogers]

Originally Posted by Bob A.

Well written Steve, but you’re going to have to do better. All I see is an air bubble which will be displaced by the fuel tank vent or carburetor vent. You did state that the car did not stall out. I'm still a believer that vapor lock can't happen in a gravity feed fuel system. I run two Harley Davidson motor cycles with gravity feed fuel system (48 years) and two model A Fords and never had a problem. These vehicles were all caught in well above 95* weather in bumper to bumper traffic for miles at a time.The bikes get so hot that the family jewels get roasted.
I use regular gas with 10% Pooh Pooh. If I could run something cheaper per gallon I would. When this "Vapor Lock" syndrome occurs in my vehicles then I would be a believer but I know it ain't going to happen because it's Bull Dung.

My sentiments exactly!!

[Tom Wesenberg]

Originally Posted by James Rogers

My sentiments exactly!!

Oh ye of little faith! May the bird of paradise curse you with vapor lock and make a believer out of you.

With a gravity feed system I didn't think it could happen either until I was riding in my friend's 29 Tudor and it died as we rounded the corner. Open the hood and let it cool for a few minutes, then we're off again. I had the same thing happen when I have to stop at red lights, but only when using the 10% crap gas. So far I haven't had a problem with straight gas. When I put the white plastic cover over the fuel line when using the 10% crap gas I also didn't have the problem.

[MAG]

Hang in there Steve. The "unbelievers" are such because it, as some admit, it has never happened to their car. It is my hope that it never does. Howver, that does not mean it does not happen. I just came back from a tour to west Texas with eight Model A's. Seven of them had the problem. Mine was one of them and I always run premium gas in it. Ask those drivers if it is real!
I have witnessed the condition as shown in your pictures. A fellow pulled ino my shop last summer with the problem. With the hood up I could see a small vortex of vapor starting at the bottom of the bowl. As it worked its way up the bubles got larger. When the surface of the fuel at the top of the bowl does not supply enough fuel to the engine it will stumble and run erractically.
All of the vapor lock problems I have witnessed will allow the engine to idle very well. But when trying to reach driving speed the voids in the fuel supply will cause the engine to run very poorly until enough air passes through the engine compartment to cool the fuel delivery system sufficiently. Then the engine will run OK.
I have had the problem with a unvented gas cap and am very familiar with its symtoms. However, if one did have a unvented gas cap and the vapor problem showed up it certainly would compound the situation.
We are presently experimenting with ways to prevent or "slow it to a walk". At one time or another, we have tried all the attempts that have been posted and some that were not. None produced good results. Except for one car, we have come up empty handed. It would be premature to state what we did. If we come up with anything I will be happy to post it.

[Bob A.]

Originally Posted by Tom Wesenberg

Oh ye of little faith! May the bird of paradise curse you with vapor lock and make a believer out of you.

With a gravity feed system I didn't think it could happen either until I was riding in my friend's 29 Tudor and it died as we rounded the corner. Open the hood and let it cool for a few minutes, then we're off again. I had the same thing happen when I have to stop at red lights, but only when using the 10% crap gas. So far I haven't had a problem with straight gas. When I put the white plastic cover over the fuel line when using the 10% crap gas I also didn't have the problem.

Tom, keep on decorating your fuel line with Baubles and trinkets and you'll be a happy camper on the side of the road

[MikeK]

Originally Posted by Tom Wesenberg

Oh ye of little faith! May the bird of paradise curse you with vapor lock and make a believer out of you.

With a gravity feed system I didn't think it could happen either until I was riding in my friend's 29 Tudor and it died as we rounded the corner. Open the hood and let it cool for a few minutes, then we're off again. I had the same thing happen when I have to stop at red lights, but only when using the 10% crap gas. So far I haven't had a problem with straight gas. When I put the white plastic cover over the fuel line when using the 10% crap gas I also didn't have the problem.

Yep the "10% crap gas" will likely boil easier than the other stuff available to you, but probably because of the "crap" factor, not the 10% ethanol. More of the unwanted refinery butane gets dumped in the low octane mix, as it does not help the R+M numbers. In Chicago, by Illinois law affecting certain counties, all grades, premium and regular, are mixed with 10% E. I prefer my corn on the cob, but in Chicago that's not the only way you get it. Shucks.

The premium grade Mobil with 10E near me appears to generate less vapor pressure than the regular E10. My lawnmower doesn't care, (damn thing jumps up and wags its tail when I walk in the garage, starts on half a pull) but when I buy the local Mobil reg. in the summer, the unvented plastic 2 gallon gas can I have swells up to a rolly-polly bottom. When I splurge and get premium (50 cents more for two gallons! ) the can behaves in the hot garage. No science, just observation of unknown relevance.

[Ron/IA]

Very interesting conversations; and I can't prove or dis-prove any of it!

But I do have another question. If the non-believers don't believe because it has never happened to them; then why doesn't it happen to them? What keeps their fuel systems from the dreaded "vapor lock"?

I wish I had the answer to that question; I think I could make myself rich! Ooooh, the Model A's I could have! - Ron/IA

[David Cockey]

"In this situation, there was vapor, but no actual “lock”. Gasoline seemed to flow sufficiently around the growing bubble, and, amazingly, the idling motor barely hiccupped when the bubble passed."

Thanks for the photos and your observations. Data is helpful.

You established that vapor bubbles can form in the fuel line. And you've also established that they can pass on through the system. No vapor lock in this situation.

Did the engine "hiccup" at all? I'd be surprised if it did. Once the bubble flowed out of the fuel line into the carburetor bowl it was vented to air through the vent from the bowl to the atmosphere. Remember, fuel does not flow directly from the fuel line into the manifold. The fuel drawn into the manifold is drawn from the fuel in the bowl. The bowl is vented to the atmosphere. As the fuel level in the bowl drops due to fuel being drawn from it the float valve opens and more fuel and and any vapor or air bubbles in the line flow into the bowl. The vapor or air then goes out the vent to the atmosphere. And fuel continues to be drawn from the bowl into the manifold and the engine keeps running..

[Bob A.]

Originally Posted by Ron/IA

Very interesting conversations; and I can't prove or dis-prove any of it!

But I do have another question. If the non-believers don't believe because it has never happened to them; then why doesn't it happen to them? What keeps their fuel systems from the dreaded "vapor lock"?

I wish I had the answer to that question; I think I could make myself rich! Ooooh, the Model A's I could have! - Ron/IA

Because we have the secret PILL !
"Beano" Buy it at your local drug store and drop two pills in your tank at fill up.

[Stan/MO.]

Now dang it, haven't you guys seen your dad put a cloths pin on the gas line for a heat sink?

[Michael P.]

I wonder if anyone with the late Zenith carburetor set up, the one with the side bowl screen filter, has had this problem?

[Bob A.]

Originally Posted by Stan/MO.

Now dang it, haven't you guys seen your dad put a cloths pin on the gas line for a heat sink?

If my dad saw me put a clothes pin on a gas line and I told him it was for vapor lock control, I would have a size 9 shoe up my a**. Dad was a mechanic with his own shop in the late '20's to some time in the '30's.