Vapor lock Really!

Virtually all gasolines contain butanes and pentanes for front end volatility (easy vaporization for startup). Butane boils at 31*F - maybe that's what we see bubbling in fuel lines and filters when underhood temps reach >200*F? And maybe that's what we see coming out of gas tanks when we remove the cap on a hot day? Gasolines begin boilng at ~70-80*F and finish no higher than 437*F. Ethanol boils at 172*F. One might think a lot of "gasoline" would have to boil off before the ethanol boiled (even considering the mixing). Check the attached distillation curve courtesy SAE Fuels Handbook. It shows the effect of ethanol and other "crappy" stuff on the boiling characteristics of a "normal" gasoline compared to "crap gas" (thanks, Tom). The depression caused by 10% ethanol generally causes hard starts on cold days, but doesn't do much (if any) harm to performance once warmed up. However, the low Reid vapor pressure of ethanol (2.3 psi) can contribute somewhat to vapor locking and the boiling point of ethanol lowers the temperature at which the vapor to liquid ratio is 20:1 (known as T20 V/L). That temperature has been found to be the best predictor of vapor lock. As several have already pointed out, you might get boiling, bubbling, hissing, percolation or whatever in your iron carburetor or fuel line, but it's doubtful vapor lock - even with the crap gas we're all dealing with. Besides, in a few years it'll be in all gasoline sold in the U.S., big city or not; better get used to it.
 

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This is my heat shield. Have not had a problem with vapor lock since I installed it.
Carb bowl stays 30-40 degrees cooler.
I made it from a piece of aluminum.

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I found some split white plastic tubing at a swap meet. It's the perfect thing to slip over the fuel line to insulate it from heat and the white reflects the heat away. It did help when I was using the crap gas, but since I've gone to good gas only I have removed it and store it under my seat.
 

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Timothy Kelly said:
Steve:

Thanks for the input.

To be clear, it was not my supposition that pure gasoline boils at a lower temperature than that laced with ethanol. Rather, it was an assertion made by a petroleum engineer.

In my post I stated: "For me, the perplexing aspect of this problem is that....per people in the know.....gasoline WITHOUT ethanol will supposedly boil at a LOWER temperature than gasoline WITH ethanol. If this is true, then why does gasoline with ethanol causes such problems (boiling in the carburetor, for example) in hot conditions when real gasoline does not?"

If in fact gasoline laced with ethanol boils at a lower temperature than pure gasoline, then the source of the issue is, at least for me, quite clear.

Timothy
Click to expand...

I'm no petroleum engineer, so I only know what I read. For example, here's an exerpt from an American Petroleum Institute document available online:

http://www.api.org/aboutoilgas/otherfuels/upload/e10_blending_study_final_report.pdf


A substantial body of knowledge has developed on the relationship between fuel volatility properties (notably, distillation, vapor pressure, and vapor-liquid ratio), vehicle performance and emissions characteristics. With the addition of ethanol to gasoline, many properties of the resulting blend (e.g., hydrocarbon type and sulfur) can be expected to more or less follow simple dilution behavior. However, the volatility parameters of mixtures of gasoline and ethanol are known to exhibit non-linear trends with increasing additions of ethanol due largely to the molecular polarity characteristics of this compound. (1)1 Lower boiling point alcohols such as methanol (65oC) and ethanol (78oC) form azeotropes with lower boiling point hydrocarbons and tend to behave more like the latter. The azeotropes of alcohols with hydrocarbons have a boiling point close to that of the pure hydrocarbon. Because of this phenomenon, the addition of an alcohol to gasoline results in a mixture that exhibits a vapor pressure that is higher than that of the gasoline portion of the blend. While the effects of ethanol on fuel volatility parameters at concentrations below 10% by volume have been relatively well characterized in the literature, the effects at concentrations above 10% are not well understood – particularly with respect to currently available commercial fuels. (1, 2, 3, 4, 5)

Higher vapor pressure means lower boiling point. Perhaps there was some confusion there.

Steve
 
Just from reading all the post I would guess it's all about how hot your eng. runs, I have been driving my 31 [stock eng] around for over 6 years now and never had the eng. stop for lack of fuel, and have never heard gas boil in my carb, and it does get hot here in Ga. in the summer.

I know Tom knows far more then I do [and I always follow his advice] about model "A" but I noticed in the pic. he put up with the white cover on his fuel line that he also was missing his eng. pans:eek:, and from what I have read they also help with the cooling of the eng. by drawing the hot air away, is that not right? Im not saying that missing eng. pans by it self would cause the over heat, but it could help.

In my simple thinking, I would say that those who have this problem, also has a eng. cooling problem.
I also burn the cheapest fuel I can buy, and no plastic fuel filter on my "A"

unless some one can tell me why some A's have this problem and some don't, all useing a stock eng. Im sticking with my eng. cooling theory.
JMHO ;).
 
In Dec 2011 we had a couple of weeks of unusually hot weather. Temperatures were in the 80s. After a 20 mile drive at freeway speeds (55-60 mph) and just after going up a long grade. I exited off the freeway. When I came to a stop the engine acted like it was fuel starved. I had to pull of the road and wait for the engine to cool down before the engine would start.

The factors here are:
Unusually hot day
Stopping after hard run
Winter fuel formulation (a more volatile mix)

Since that time it has happened again under similar conditions. I found that I can keep the engine going if I open up the GAV 1-3 turns. Once I am moving again it only take a few minutes with the GAV opened up for the problem to go away.

Bob
 
Some do, some don't, mine does not in florida heat during a parade.

Good luck to those that have the problem I hope you find the answer and can enjoy your car always.
 
I've noticed over the years in these threads that Model A drivers down south are frequently mystified why the rest of us have more vapor lock problems than they do. My theory is that the gas sold in the south is more vapor lock resistant. There are about 20 different blend grades sold around the country, depending on the season.

Here is some Reid Vapor Pressure specs for seasonal grades:

Normal RVP values look like this:
January-March RVP is 13.5+ in many areas
April-September RVP is 7.0-9.0 in many areas
September-December RVP is 11+ in many areas

The RVP is the vapor pressure above the liquid at 100 deg F. The vapor pressure increases with liquid temp until it reaches atmospheric, 14.7 psi, at which point the liquid boils.

Those RVP differences look substantial to me. Although the EPA's motivation is pollution control by minimizing evaporation of gasoline, I think the data explain a lot of vapor lock problems. I doubt that they ever get the winter blend down south. I've noticed that the frequency of vapor lock problems and FordBarn posts tends to taper off later on in the summer, after everyone's using the summer blend.

The summer blend is more expensive to produce because butane and its ilk are relatively cheap. It also give sligthly better mileage.

Steve
 
Guys,
I asked if you personally have ever had a vapor lock in your Model A. I believe everyone know about the causes and cures of vapor locks.

Please just yes I have or no I haven't on my stock Model A Ford. I gathering data not hear say.

Thank you
 
59mgaguy said:
Guys,
I asked if you personally have ever had a vapor lock in your Model A. I believe everyone know about the causes and cures of vapor locks.

Please just yes I have or no I haven't on my stock Model A Ford. I gathering data not hear say.

Thank you
Click to expand...

no I haven't on my stock model A ford
 
Last edited:
A suggestion: Use the website's utility for creating a poll.

Another suggestion: Expand the question to include high compression heads, and maybe other common modifications, so I can participate.

Another 'nother suggestion: Expand to include car year. The 28-29's have a more cramped engine compartment. I've often wondered if that makes a difference.




59mgaguy said:
Guys,
I asked if you personally have ever had a vapor lock in your Model A. I believe everyone know about the causes and cures of vapor locks.

Please just yes I have or no I haven't on my stock Model A Ford. I gathering data not hear say.

Thank you
Click to expand...
 
59mgaguy, when you initially started the thread, and you clicked "Start a new thread", at the very bottom of the page is an option for a poll where you can set up the parameters of the question with up to 4 options for answers. I believe the results are then given in graph form as the poll progresses. Just FYI
 
"Yes" I've had vapor lock about 3 time back 47 years ago in a Model A. Put 4 cloths pins on the line and never had it to happen after that and the pins soon lost off. This was before crap gas.
 
To those who politely point me out to using the Poll I apologize. After multiple eye surgeries and radiation I find it a little hard to read at times. So I apologize.
 
I live in Houston, TX and it does get hot sometimes and I have driven Model A's for 27 years and never had a vapor lock. Plus for the first time in 27 years of driving them a lot, I had my first break down. Horn wire shorted out and blew a fuse. John
 
59mgaguy said:
Guys,
I asked if you personally have ever had a vapor lock in your Model A. I believe everyone know about the causes and cures of vapor locks.

Please just yes I have or no I haven't on my stock Model A Ford. I gathering data not hear say.

Thank you
Click to expand...

Yes. Two days last year. Over 95 degrees outside temp. both times.
 
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