Fuel vaporization experiences on Ramblers

My first experience with fuel vaporization goes back to 1973 when I was 11 years old and our family was traveling back from a holiday at Lakes Entrance in our 1964 Classic V8 Sedan.  The issue started when the car would not climb a hill so Dad pulled over but it idled OK, revved OK but once we took off it would just die.  Eventually we got home (very stressed though) and the mechanic checked out the fuel system and found nothing unusual so put it down to a fuel blockage.  It wasn't until later that I realized this was probably fuel vapour lock!

This happened a couple of other times over the next few years and always on holidays it seemed.  We had a theory that it coincided with filling up with BP fuel and warm weather.  The other times it did not stop our progress just an occasional drop off and pick up again - not a good feeling.

When I got my licence the Rambler was mine and I used this 64 Rambler Classic for 7 years and never had any such trouble.  I have heard of other members experiencing this problem but I never had the problem until we drove a 64 Ambassador from Chicago to LA on route 66 in 2009.  It was a constant problem in the warmer sections of the trip especially at higher altitudes however amazingly enough it never totally stopped the car running just slowed us down.

My most recent experience was driving my 66 Classic V8 from Newcastle to Sydney on a warm day.  Part way into the trip found myself in a line at road works and the engine was already showing a little above half way on the temp gauge.  Waiting in the road works put the temperature up a little more and I was just able to roll to the side before stopping totally.  After 20 minutes of cooling the engine I was able to start again and continue.  There was one large hill that I knew would be a problem.  I was trying to keep the motor cool by traveling at 50mph and with the heater on full.  However I got stuck behind a truck and had to slow to 35mph and then needed to over take and that was it, fuel vapour lock again!  This was the worst I have experienced and I finally got home.  But how to stop fuel vapour lock occurring?

Fuel vapour lock occurs when the fuel boils (turns to a gas) on the way to the carburetor.  Since the fuel pump in older vehicles is sucking fuel from the tank it vaporizes more easily at a lower pressure.  Once it is a vapour the pump can not pump a gas.  Now sometimes there is enough fuel in the carburetor to keep the motor running until the vapour lock clears so it is possible for it to occur without you being aware.  It is only when the fuel in the float bowl is getting low that it affects the running of the vehicle. 

So what are the factors in vapour lock occurring:-

  • Weak fuel pump (an old time US mechanic said this was a factor in our 64 Rambler vapour lock).   This may explain some cases.
  • Different grade fuels with lower vaporization point (e.g. Ethanol blended fuels)
  • High temperature of exhaust manifold directing heat on to the fuel line and fuel pump area (this is the reason for vapour lock occurring up hills as the exhaust temperature rises greatly with increasing load on the engine)
  • Old style fuel pump pulling fuel under suction means this happens at a lower temperature than if it was under pressure.

What to do when it happens on the highway?

  • Stop and open the bonnet and let things cool
  • Don't use all the fuel from the carburetor bowl by pumping pedal to keep going (makes it harder to start when it does cool down)
  • Pour water near fuel line/exhaust manifold area
  • Old time mechanic says add 1 litre transmission fluid to the tank to prevent fuel vaporization (we tried this and it seemed to work)
  • Once you get moving again try to travel at an optimum speed to keep the engine cool and take it gently up hills, use a lower gear to keep engine from lugging.  This lowers exhaust temperatures and helps prevent overheating.

What can be done to reduce the occurrence of vapour lock:-

  • Check fuel pump condition.
  • Make sure an aftermarket inline fuel filter has not been installed between the fuel line and the fuel pump (adds extra resistance)
  • Shield fuel line from exhaust heat (not easy on Ramblers)
  • Use fuel without ethanol
  • Keep engine temperature down with an efficient cooling system
  • Install an electric fuel pump at the fuel tank end of the line.  I found an electric in line pump that fits very neatly in the middle of the flexible hose between the tank and rigid fuel line.  Wiring then needs to be run to the fuse panel.

Contributed by Technical Officer Rohan Borrell