Vapor lock-Comments ?

[Herman Desser]

Does anyone know how one can find out the "flashpoint" or boiling temperature of gasoline.  I have heard many stories that since lead-free gasoline now has quite a bit of ethanol in it and the lower the octabe the higher the "flashpoint".  Higher octanes, to avoid "pinging", ignite at a lower temperature thus one way to buy time on vapor lock is to use lower octane fuels as long as you can still avoid pinging. Of course one can install an electric fuel pump but this should not be necessary if we find the right gas mixture.  I have also heard you can put in a quart of diesel fuel per tank of gas to lessen the problem of vapor lock..

Commnets are appreciated

[Brad Ipsen CLC#737]

Chevron has a great web site that explains the fundamentals of vapor pressure, distillation curves and vapor/liquid ratio.  

http://www.chevron.com/products/prodserv/fuels/bulletin/motorgas/1_driving-performance/ TARGET=_blank>http://www.chevron.com/products/prodserv/fuels/bulletin/motorgas/1_driving-performance/

[Fred Garfield 22310]

If vapor lock during hot weather city driving is the only concern, why not just insulate the fuel line?

[Bill Sullivan]

Insulating a fuel line is not effective -- because the heat in the engine compartment will eventually get through the insulation.  Insulation may help delay the onset of vapor lock, but once it happens to an insulated line, you will have a difficult time cooling the line.

Cooling a fuel line can be helpful, if you can route through a place where outside air can blow over it.  Sometimes I have used wet rags over a line to cool it, and that can help get a vapor locked car going -- until the line heats up again.  

Vaporization of fuel does not just occur in the fuel lines, it also happens in carburetor bowls and fuel pumps.  When that happens, the mixture leans out and the car runs poorly or not at all. If the fuel you have is too volatile, it can be impossible to get anywhere on a hot day.  The only cure is is to just sit until everything cools off enough to stop boiling the fuel.  Then you can start and be on your way for a while until the car heats up again.  Vapor lock comes and goes: depending on the time of day, the load your car is under, how fast you are driving, what kind of gas is in it, etc.  Because of this, it is easy to think you have solved the problem when you havent  -- it merely went into hiding.  

There are many legends about how to deal with this, such as putting tin foil or clothes pins on the fuel lines.  I think most are myths, though if gimicks can cool the lines or fuel system components, they may help a bit. Electric fuel pumps help, but not always.  I had one Buick straight eight that handled vapor lock far better without an electric fuel pump in the line.  My LaSalle prefers an electric pump.  Go figure!

10percent Ethanol (gasohol) is much worse than regular gasoline in its propensity to vapor lock, that has been my experience, what is yours?

Best advice I have:  If your car likes to vapor lock, drive on a cool day if you can...

Bill.  

[Fred Garfield 22310]

Thanks for the detailed post, Bill. Ive only owned one car that had a vapor lock problem. Thats my 71 Dodge V8. It only locked up on hot days in stop/go city traffic. I applied insulation only to the segment of fuel line running under the car, bypassing the part in the engine compartment. In roughly 8 years, Ive had no further problem with vapor lock.

[Bruce Reynolds # 18992]

Gday Bill,

The biggest cause of "vapour-lock" I have found is where the engines mechanical fuel pump cannot draw fuel from the tank because the heat coming up from the road surface heats the fuel line as it passes from the tank, under the car, to the front.

A Fuel Pump cannot draw vapour, and if the road surface is hot enough the fuel travelling slowly in the line can vapourise.  I know from experience.   Travelling at any speed above slow traffic, and there is enough air passing under the car to cool the fuel will line.

If you are getting Vapour Lock at the Carby or line from the pump to the carby, you can bet that the problem is in the line from the tank to the pump.   A pump will always pump fuel to fill the carmy, but it cant if it cant get fuel from the tank.   A pump cannot pump air.  It can only pump fluid, and a fluid will fill an empty carby.

You have to remember that the air temperature is taken in the shade, and the sun beating down on a road surface will heat it up a lot hotter.

Bruce,
The Tassie Devil(le),
60 CDV

[Rhino 21150]

I have heard of adding diesel fuel also, have never tried it. I doubt it would hurt your engine adding so little.
Clothes pins work, depending on the car. My dads 40 La S has them. They work (in this case) by disrupting the (HOT!) air flow from the fan blowing across the tubing that runs across the top of the engine. I have suggested insulation but he doesnt like the idea, no reason given. I have the insulation on my 38 La S, never locked. I suspect the foil would work in a similar fashion.
If the problem is persistant, try adding an air intake hose to an air source in front of the radiator. The cooler air will keep the carb from boiling. When the hose on my 67 Fairlane rotted away I had vapor lock irregularly until I replaced it. All modern cars use a hose of some sort.
Electric fuel pumps do their best work when they are located at the rear of the car, away from the exhaust. This puts the fuel under pressure all the way from the rear to the carburetor. Gas under pressure has a higher boiling point than gas being sucked. This eliminates the hot road surface problem. My 61 Econoline had this plus a heat shield near the fuel line and the brake lines. They got hot from the oversized engine and exhaust.
Make sure that if the car came with an insulating gasket under the carb that this piece is still there. GM NEVER USED PARTS THAT WERENT NEEDED.
BTW, what ya drivin?

[herman clc #19416]

Seems that most of the comments are about the same..

Did find out from an Oil Company webb site that the lower grade gasolnes, like 87 octane has a higher boiling point than 92 octane.  And was also told to try to buy gas a few days or week earlier before an anticipated trip when hot as the gasoline tends to evaporate some of the enthanol thus making it less volatile, not sure of this statement,.  We also found some silicone tubing that can withstand 550 degrees of heat and have wrapped around the fuel line from the pump to the carb and will see what happens. Have filled tank with 87 octane and wrapped fuel line, Next is electric fuel pump if still having problems.
 
By the way this is a 1948 6267X, fresh motor and restoration and hope to see you all at the GN in Orange.

Herman

[Bryson Talamini CLC 21505]

As others have stated, the pump cant pump air so you get vapour lock. Technically the pump is cavitating and there are two solutions in our cars: lower the temperature of the liquid or reduce the losses in the suction piping. If you do both you can insulate the piping from the tank to the pump inlet and replace this line with piping of a larger internal diameter, which greatly reduces the suction losses. I replaced the 1/4" ID on my 37 LaSalle with 3/8" ID, which doubles the cross sectional area, and this eliminated the problem. The pump body and its inlet piping in the engine compartment get quite hot and this it where the fuel absorbs most of its heat, especially when idling and climbing long hills on a hot day.
Bryson in Oz

[Bryson Talamini CLC 21505]

Herman
I forgot the obvious: Modern fuels are more volatile and therefore more prone to cavitation. The 1/4" piping was fine for the lower volatility fuels of the thirties.  Adding diesel will reduce the volatility, but this is messy and its hard to ensure good mixing. To me it doesnt seem worth doing.
Bryson in Oz

[Larry]

One problem I had with my Hudson was trying to keep it original for judging purposes. This makes alterations to the fuel pump/fuel line difficult. I have some fuel line insulation that I purchased in an oversize diameter and cut it open to attach velcro. Im able to put it on and take it off easily. I also installed a 6-volt electric fuel pump near the gas tank on a hidden switch under the dash. If vapor lock does occur (usually after being stopped at traffic light, etc.), I start the electric pump and this cures the problem. I then turn off the pump. This also is good for a back-up pump in case my mechanical pump fails.

[Jeff Maltby #4194]

I can assist you Herman :<)