Vapor Lock or Bust

[Merrill Davis]

I agree. What are you running for a fuel pump? Today's ethanol laced fuel has a lower boiling point so anything that can be done to insulate the lines from heat or isolate the carb from heat transfer from the engine is a good thing. Fuel additive to combat the negative effects of the ethanol may help a bit too. I added an electric pump back by the tank on my Imperial in the hopes of helping the mechanical pump still in place recover quicker from evaporation.

 

[Merrill Davis]

DetMATT 1 I thought the very same thing. I wonder if the gas is a problem. I am running nothing but hi-test. I may run the pure gas that I can purchase in several places in town. It is more expensive but it may help. Thanks for your response again. I have a number of ideas to try. I will keep you posted. The Challenger does run great though when it is running. I am rebuilding another 340 engine right now. Love it!

 

[Merrill Davis]

Make sure the metal fuel line along the right front is not near the exhaust. Also, a carb spacer may help. And blocking off the manifold carb passages. Nothing wrong with Holley, in my opinion.

 

[Merrill Davis]

Thanks Adam. Your ideas are spot on. I will check it out. Some vouch for the clothes pin. I may have been a bit unwise and hasty to make the remark. It can ride along with the dust as far as I am concerned!!!!! Have a good day.

 

[Steve340]

Steve, it does sound quite similar. It sounds like it is all choked up and needs to be BLOWN out. There is an electric choke. It is not manual. Thanks for the response. I know there is a fix. I thought about changing the Carb but some say it is not the carburetor.

Your problem may be to much fuel. Don't change the carb. Try this it is pretty quick, easy and reversible.
Do not pump the gas pedal when hot and disconnect the feed to the choke. Be careful when you get back in the car to not bump the gas pedal. Remove the feed wire to the choke and insulate the wire as it will have 12 volts from the ignition probably. Remove the little round black choke spring housing and wire the choke flap off or open. Try in that position for a few days.
Cold starts will require a few pumps on the pedal as what I have told you will render the choke inoperable.
With my car the choke was coming back on and flooding it.

 

[tonysrt]

Could somebody explain how a wooden clothes pin extracts heat from a metal fuel line? If we use wood as an insulator between a carb and manifold what am I missing. I never saw a metal clothes pin, I've seen plastic but no metal. Now a metal clothes pin would probably pull heat away.

 

[Slade Caltrider]

Could somebody explain how a wooden clothes pin extracts heat from a metal fuel line? If we use wood as an insulator between a carb and manifold what am I missing. I never saw a metal clothes pin, I've seen plastic but no metal. Now a metal clothes pin would probably pull heat away.

They do not extract heat. They cause air flow to be disturbed around the cloths pin and the steel line that increases cooling effect in that area of the line. Nothing more. The pin itself does not pull heat from the line.

 

[tonysrt]

That helps explain a little. But in stop and go traffic no real benefit. Unless fan is moving the air. Doesn't the heat become a problem when you shut down and things start to percolate. I've noticed temp gauge rises after shut down which shows that the engine heat is being transferred to water but now there's no more circulation to cool things down. I think B & hemi engines are more resistant to heat soak because no water in intake maniflold.

 

[Slade Caltrider]

That helps explain a little. But in stop and go traffic no real benefit. Unless fan is moving the air. Doesn't the heat become a problem when you shut down and things start to percolate. I've noticed temp gauge rises after shut down which shows that the engine heat is being transferred to water but now there's no more circulation to cool things down. I think B & hemi engines are more resistant to heat soak because no water in intake maniflold.

In stop & go traffic it still helps if you are running a constant belt driven fan on the engine. It is the air coming off the back of the fan that blows across the engine that hits the cloths pin and deflects around causing a low air pressure around the pin and line area, thus cooling. It is an old trick that was used over the years to help cool the gas before it entered the carb. I would not use this as a fix. Just get the steel line so its not touching the hot metal engine block or heads and get the inline gas filter into the fan air flow in front of the carb. As far as engine temp rising after hot shut down, it does get much hotter by 20-30 degress for about 5-20 minutes after turning the engine off due to no coolant flow, totally normal for all engines. It will also boil the gas and cause the gas to expand and push out of the float bowls and into the throttle bores of the carb into the intake manifold runners and into the cylinders. Thus you have a badly flooded engine on hot restart. The grade of gas has nothing to do with it. Yes, R & RB engines have dry intakes and do not have quite the heat generated in the carb area on hot shut down. Also aluminum intakes do transfer heat to surounding metal components like carbs and heads much more then a cast iron intake manifold. Try touching an aluminum shifter knob that has been setting in the sun on a hot day, it will burn your hand to touch, heat transfers to your hand much faster then a plastic or steel knob.

 

[DetMatt1]

1 of many articles about ethanol you should find useful.
A BIT ABOUT ETHANOL

Ethanol gas is typically known as “E10” or 10% ethanol and 90% petroleum gasoline. It is more formally known as “ethyl alcohol” and is derived from a variety of crops including sugar cane, sugar beets, potatoes and most commonly in the U.S., corn. Ethanol contains 34% less energy per unit volume than gasoline although it does have a higher octane rating.

The U.S., while not the largest producer (that would be Brazil), is still a heavyweight in ethanol production with 13.9 billion gallons produced in 2011. Up to a year of so ago, it was possible to get non-ethanol fuel at some gas stations (that usually imported it from Canada) in nearly any state. Those stations are now non-existent in many states and disappearing elsewhere.

If ethanol is new to your area, and you are just starting to use it, the first word of caution is: Watch your fuel filters. Ethanol is an excellent cleaner and solvent. Most of your carburetor cleaning products contain ethanol (or a variant) as their primary ingredient. That layer of sludge in your tank or fuel lines that has been pretty much inert up to this point may be dissolved by the ethanol and plug your filters with a tar-like substance pretty quick. Keep and eye on them and carry spares. Usually, most of the material that will readily be dissolved is out of the system within a season of using ethanol.

What you may not realize is, in most cases, ethanol is blended into the gas at the station pump. While it is not supposed to exceed 10%, the percentage is not monitored that closely. Ethanol rates can vary dramatically. This is your first challenge and one you may not have a lot of control over, although sampling kits are available.

The ethanol they are blending in with your gas is hygroscopic, meaning it will readily absorb water. How readily? It will absorb water at a rate 50 times faster than conventional gas. If you recall the old gas line antifreezes, there were three types – methanol, ethanol, and isopropyl. You don’t see them around much anymore as the 20 gallons of gas you just put in your MV has 2 gallons (10%) of it included!

A very common complaint about E10 gas is that it does not keep (store) well. This is absolutely true. As the ethanol continues to absorb moisture, it begins a phase separation.

During this phase separation, the ethanol rich fuel separates from the remaining fuel (making it ethanol deficient), leaving you with two fairly distinct fuels in the tank.
Over time, this creates two layers of fuel: The top will have fuel that has very low octane (ethanol deficient), and the fuel at the bottom (the ethanol rich water layer) that is extremely corrosive. This creates a real challenge to any vehicle collector. Vehicles will sit for an extended period of time without use, allowing this phase separation to occur.

If you own any gas powered lawn equipment or anything with rubber hoses and gaskets, you likely have experienced the effects of alcohol that has been further enhanced by concentrating it via phase separation. The symptoms can either be poor performance from the ethanol deficient fuel due to low octane, or deteriorated components from the ethanol rich fuel. Many rubber and plastic components are particularly susceptible to ethanol degradation.

 

[DetMatt1]

FIGHTING THE EFFECTS OF ETHANOL

While not ideal, there are a few solutions that do help. First, use fresh gas. Under ideal conditions, E10 gas has a shelf life of 100 days, or roughly three months. Left to its own, it will have significant separation after that point causing poor performance and greater deterioration of susceptible components.

Secondly, absorbed moisture is the enemy. Take steps to control it: Keep gas cans sealed; store your gas in a location where there are not big temperature swings to cause condensation and keep your tanks full. Air contains moisture and allows for condensation. So, the less air, the less moisture.

Many of us in the northern areas of the country do not use our vehicles in the winter, so this leaves a full tank of fuel that will cause issues if left over the 100 days. Fortunately, there are products that will delay (not stop) the effects of phase separation.

Two major brands are Stabil and StarTron, although there are a number of others marketed under a variety of names. I recommend using both religiously when you add gas to your vehicle. I have used both successfully, but I believe StarTron does a better job of negating the effects of the ethanol. Having dealt with many deteriorated fuel lines on vehicles and equipment, I switched to it a couple years ago and have not had a problem since. Keep in mind any stabilizer must be added before phase separation occurs.

One final tip on additives: Fuel stabilizers and upper cylinder lubricants (ex. Marvel Mystery Oil) are the only additives that are recommended with ethanol. Any of the ‘cleaning” type products such as carburetor/injector/engine cleaners contain high levels of alcohol as their primary ingredient. All you are doing is adding more of the same ingredient that is likely causing your issue to begin with!

Contrary to any claims, the effects of phase separation are irreversible. Bad gas will never become good again.

 

[DetMatt1]

BACK TO VAPOR LOCKS

So let’s circle back to the vapor lock issue. Vapor lock is closely related to the volatility of gasoline—that is, the gasoline’s tendency to vaporize under a given set of conditions. The unit of measurement for volatility is known as “Reid Vapor Pressure” or RVP—vapor pressure of gasoline at 100 degrees Fahrenheit. It is actually measured by placing a specific quantity of gas in a sealed ‘bomb,” shaking it and reading the attached pressure gauge.

Normal atmospheric vapor pressure (the pressure of air above our heads) is about 14.7 lbs/sq/in. Any liquid that has a vapor pressure greater than the atmospheric pressure (remember, this is typically 14.7) will boil. The higher the RVP rating, the greater the tendency of fuel to vaporize (and vapor lock).

Fuels sold in the winter are blended to have a higher RVP than those in the summer to aid in starting. By increasing the RVP, they lower the boiling point and increase its volatility so it takes less to turn it into vapor and hence start in the cold. In the summer, the warm temperatures are already assisting in the vaporization process so the gas itself doesn’t need to be as volatile.

Winter: High RVP = Lower Boiling Point = Faster Vaporization
Summer: Low RVP = Higher Boiling Point = Slower Vaporization

Raising the winter RVP is usually done with the addition of butane that is very volatile (high RVP) and inexpensive. The highest RVP gasoline commonly sold will have an RVP of around 15.0psi (measured at 100 degrees F). If that gas were in your tank on a hot summer day when the temperature reaches 100 degrees, it will boil in the tank. On a 70 degree day, the heat in the engine compartment will reach well over 100 degrees, especially in a parade or at rest.

Vapor lock often occurs when you first stop and shut off the engine as the temperature in the engine compartment will dramatically rise with no airflow. If the gas in that truck has an RVP of 15 and the atmospheric pressure is 14.7 you will have the gas boil in the engine compartment (carburetor) and enjoy what you commonly know as “vapor lock.”

The RVP standards do vary throughout the country as the RVP in Duluth, Minnesota, needs to be significantly higher in winter than that in Jacksonville, Florida. If you live in a northern climate you probably experience the full range of RVP rated gas through the course of the year. This is very important to note.

Remember that I had vapor lock at the Memorial Day parade even though I thought I had the problem licked? My inspection on this truck was due in early spring, so while it was out, I filled up the gas tank.

I live in a relatively rural area, so the gas station probably gets filled every couple weeks. Depending on the volume of business a gas station does, I could have easily filled the truck with Class D fuel with a boiling point of just 131 degrees. Do you think the engine compartment could reach 131 degrees on an 87 degree day moving along at parade speed of about 3 mph? You bet! Add to this, ethanol raises the RVP by an additional 1 psi (from 13.5 to 14.5). There is no question boiling can occur. In general, it can be said that ethanol will increase the likelihood of vapor lock by 10% just because it raises the RVP so much.

It was the perfect storm of low boiling points and hot engines. Like taking the cap off of a very hot radiator, and having it violently boil and steam, boiling is most likely going to occur where there is a sudden drop in pressure. This can happen just prior to the fuel pump or as the fuel enters the carburetor bowl.

At one of these points, the slight pressure created by the fuel pump within the fuel line will drop to zero, immediately lowering the boiling point. As the fuel boils, it turns to a frothing combination of boiling gas and vapor. This vaporish, boiling brew will not flow and is highly resistant to pumping, so normal flow will cease until it cools back to just liquid.

These issues are pretty much restricted to carbureted engines. Newer engines with fuel injectors are generally not susceptible to vapor lock.

 

[DetMatt1]

SOLVING VAPOR LOCK

So what is the solution? You have two options: Raise the boiling point or cool the fuel. All remedies will address one of these two issues.

In the case of my own vehicles, I now know it is best to fill them during the summer months when the RVP rating is the lowest, giving me the highest boiling temperature. I rarely use my trucks in the winter, and when I do, it is usually mild enough that starting isn’t an issue.

Cooling the fuel will also work. This can be as simple as opening the hood and letting it cool on its own or putting a wet rag around the carburetor, where the boiling is likely occurring, to get it cooled down.

One of my trucks was much more prone to vapor lock than the others. One of the suggestions made to me was to remove the metal in-line filter that I had added to the gas line toward the front of the valve cover. It hung less than an inch or so above the valve cover and was a great heat exchanger to absorb the engine heat and add even more heat to the little bit of gas flowing through the system during a parade or idling. Removing that filter was a good idea and did stop the vapor lock issues until this spring.

If you don’t have a Bakelite spacer between your carburetor and the manifold, then I suggest you get one. It prevents the manifold heat from being transferred directly to the carburetor.

Insulating the fuel lines near the engine may also help. There are wraps available for this very purpose.

Replacing a mechanical fuel pump on the engine with an electrical pump close to the fuel tank can also reduce the fuel line vapor lock problem. The electric fuel pump eliminates the mechanical fuel pump as a source of heat, provides greater pressure on the line and hence increases the boiling point, as well as being able to overcome lesser degrees of vapor lock. Lastly, hot fuel with vapor can be pushed much easier than pulled as your mechanical fuel pump does giving some advantage to an electric fuel pump.

 

[DetMatt1]

Tips to Avoid Vapor Lock

• Remember there are only two ways to prevent vapor lock – cool the fuel or raise the boiling point
• Avoid using winter formulated fuel in the summer
• Use the lowest octane fuel you can that still avoids “knock’
• Keep fuel lines from direct contact with hot engine parts
• Remove fuel filters that may be directly over the engine and manifold

 

[Merrill Davis]

Your problem may be to much fuel. Don't change the carb. Try this it is pretty quick, easy and reversible.
Do not pump the gas pedal when hot and disconnect the feed to the choke. Be careful when you get back in the car to not bump the gas pedal. Remove the feed wire to the choke and insulate the wire as it will have 12 volts from the ignition probably. Remove the little round black choke spring housing and wire the choke flap off or open. Try in that position for a few days.
Cold starts will require a few pumps on the pedal as what I have told you will render the choke inoperable.
With my car the choke was coming back on and flooding it.

 

[Merrill Davis]

Thanks for the info. I think, without celebrating too quick, the problem has been solved. I put a insulation sleeve on the metal gas line running to the carb. I drove and stopped four times yesterday and cut the motor off. Did not touch the accelerator and it started each time. This may have done it. I kept the clothes pin on for good measure

 

[Merrill Davis]

Tips to Avoid Vapor Lock

• Remember there are only two ways to prevent vapor lock – cool the fuel or raise the boiling point
• Avoid using winter formulated fuel in the summer
• Use the lowest octane fuel you can that still avoids “knock’
• Keep fuel lines from direct contact with hot engine parts
• Remove fuel filters that may be directly over the engine and manifold

 

[Merrill Davis]

Great information. I put an insulation sleeve on the metal gas line running to the carb and so far, it seems to be the trick. The car starts every time. I touch the gas pedal lightly on cold start and do not touch it all on warm starts. I plan not to celebrate too early, but so far, all is well. Thanks

 

[Merrill Davis]

SOLVING VAPOR LOCK

So what is the solution? You have two options: Raise the boiling point or cool the fuel. All remedies will address one of these two issues.

In the case of my own vehicles, I now know it is best to fill them during the summer months when the RVP rating is the lowest, giving me the highest boiling temperature. I rarely use my trucks in the winter, and when I do, it is usually mild enough that starting isn’t an issue.

Cooling the fuel will also work. This can be as simple as opening the hood and letting it cool on its own or putting a wet rag around the carburetor, where the boiling is likely occurring, to get it cooled down.

One of my trucks was much more prone to vapor lock than the others. One of the suggestions made to me was to remove the metal in-line filter that I had added to the gas line toward the front of the valve cover. It hung less than an inch or so above the valve cover and was a great heat exchanger to absorb the engine heat and add even more heat to the little bit of gas flowing through the system during a parade or idling. Removing that filter was a good idea and did stop the vapor lock issues until this spring.

If you don’t have a Bakelite spacer between your carburetor and the manifold, then I suggest you get one. It prevents the manifold heat from being transferred directly to the carburetor.

Insulating the fuel lines near the engine may also help. There are wraps available for this very purpose.

Replacing a mechanical fuel pump on the engine with an electrical pump close to the fuel tank can also reduce the fuel line vapor lock problem. The electric fuel pump eliminates the mechanical fuel pump as a source of heat, provides greater pressure on the line and hence increases the boiling point, as well as being able to overcome lesser degrees of vapor lock. Lastly, hot fuel with vapor can be pushed much easier than pulled as your mechanical fuel pump does giving some advantage to an electric fuel pump.

 

[Merrill Davis]

great stuff. Thank you for your insight and time. I will investigate the Bakelite. Makes sense to me. So far so good on the insulation sleeve on the metal gas line.