Vapor lock in spring?

[Matt Innocenzi]

I have a '58 Cadillac SDV.  When using it in the summer, it would start fine and run beautiful.  However, after I parked it and let it sit for 20-30 minutes, it would fire right up, go 500 feet, and then run out of gas.  If I let it sit for about an hour, it will fire right up again as if nothing happened.  I figured for the summer time, it had to be vapor lock and was able to live with it.

Yesterday, I took the car out for a ride.  It was 65 degrees F.  I drove the car 10 miles, parked it, came out 20 minutes later, it went 500 feet and died.  The carburetor was bone dry and little fuel in the filter bowl.  I disconnected the lines on the fuel pump, sucked on it and got a mouthful of gas so I know the lines are free, and put them back on the pump.  Cranked the engine, nothing.  I let it sit an hour, came back to it, and it fired up as if nothing happened again.

Besides being haunted, what is going on here?  I know I can fix it with an electric in line pump, but I am more interested in the academic science of what is physically going on that the original mechanical fuel pump works intermittently.  Could it be the push rod for the fuel pump is getting hung up?  I have had three mechanical fuel pumps on there and each one had this problem, so I know it is not the fuel pump. 

I am interested in knowing if anyone else shares this problem.  It is a brain teaser.

Thanks!
Matt

[joeceretti]

All the hallmarks of vapor lock... 3 ways to fix it. 1) Get a time machine and buy some old real gas. 2) Put an additive in the gas to reduce the tendency to vaporize. 3) Add an electric pump near the tank to keep the pressure in the lines high enough to stop the vaporization.

I don't have all the parts of my time machine, yet, so I went with option 3. I figured option 3 has less of an ongoing cost/annoyance. Although a bit of diesel fuel in the gas should solve it.

[Matt Innocenzi]

Joe,

So it is not uncommon to have vapor lock in spring or winter?  I suppose it is more the heat from the engine that is causing it to boil rather than the ambient air temp.

I put marine stabilizer in all my old cars to counter the ethanol and preserve the gas.  Is there another additive that will reduce the tendency for vapor lock?  I never heard of the diesel fuel approach.  Any negative impacts that could present?

Thanks!
Matt

[Matt Innocenzi]

Thank you Jon.  Sorry I missed your previous posts.

[David Greenburg]

Matt:

You've got the classic symptoms of vapor lock, and while its most common with high ambient temps, it can occur any time the fuel gets too hot.  In addition to the advice above, I'd check to be sure the engine isn't running hot for any other reason  (low on water, loose belts, clogged radiator,  stuck thermostat).  Also, is the flexible fuel line running from the frame to the pump too close to the exhaust?  Finally, while ethanol certainly increases the potential for vapor lock, the fuel stabiliEr should help that.  Is it possible you've got a particularly lousy tank of gas?

[Scot Minesinger]

This is an a/c car right?, so it has a fuel line return.  Vapor lock should not be as much of a problem as a non a/c car.

This happens to my 1970, but it does not die, it is just hard to start if hot (over 75'F) outside due to fuel boil off.  If it sits for ten minutes or less no problem.  If it sits for 15 minutes to two hours, it starts hard.  On a hard start I have to give it gas for 20 seconds or so, or it will die.  When the engine shuts off, it so hot all the fuel boils out of carb.  On this forum a man with a 73 had the same problem and he used an electric fan with a wind up timer.  If he used the fan the car started nice when hot outside.

Again usually the a/c cars with return fuel line do not suffer from vapor lock. 

[n2caddies]

On my 60 I had the same experience and finally figured out that the screws that hold the two halves of the fuel pump together had become loose enough that air was getting in preventing the pump from pulling the gas through the lines. I simply went around it with a screw driver and tightened them up. That was 2 years ago with no more issues. Also some of the Airtex fuel pumps made in Mexico were garbage and caused lots of similar problems.
Randy

[m-mman]

May I make a suggestion? Check/replace your fuel pump.

Vapor lock happens ONLY when the fuel that is in the line BOILS in the line, and only from ambient heat. You are correct to be suspicious of 'vapor lock' in 65 degree weather.  You got a lot of feedback & confirmation to your vapor lock diagnosis. I wonder what would have been suggested if you had only described the symptoms you were having without offering a diagnosis. 

1. You stated that you could easily draw fuel from the tank. (by mouth even!)  This means that there are no obstructions or problems on that side of the pump.
2. You stated that the filter/carb was empty when it stalled. (so the problem is not ignition related)
3. What is the ONLY thing between the fuel line and the carb . . . . ?

People seem quick to condemn the fuel mixes we are using today compared to what was pumped years ago. Ok . . . but isnt one of the big differences between now and then the inclusion of alcohol??  And what effect do we all know alcohol has on rubber parts? Especially fuel system rubber that was engineered for non-alcohol ingredients. . . . .

I mention this because I just worked on a friend's 1960 Edsel that had the exact same symptoms. I fixed and rebullt stuff all over the car so he could take a cross country trip. I did not replace the fuel pump - because it seemed to be working fine - He reported 'vapor locking' the entire time. <yuck!> Actually his symptoms were stalling from lack of fuel and not running again for an hour or so.

He limped home and my checks showed good fuel pump pressure and flow. I rechecked the fuel system from the tank to the carb . . . Finally I gave up and got a fuel pump.  It worked perfectly and has had no problems for the last several months.

To further cloud the issue someone (badly) installed an electric pump on the trip, it didnt change anything. It buzzed and thumped and I thought it MUST be working. After a complete check it was only buzzing and thumping but is wasnt pumping. BUT EVERYONE THOUGHT IT WAS (including me) so we all assumed vapor locked or plugged lines. Did alcohol ruin it too? I donno I just removed it.

The thoughts about fuel pump push rods and loose screws are also good things to check. But vapor lock? Naw, I dont think so.

[Roger Zimmermann]

Maybe one valve into the pump was disloged, or you have dirt in one of the valve preventing the valve to close.

[Matt Innocenzi]

Hello all,

This is great discussion and I appreciate all of the advice.  Yes, my Cadillac is an A/C car and it does have the return line to the tank. 

The fuel lines are metal and clipped to the frame until they get to the front of the engine where they (meaning the supply and return) convert to rubber.  The rubber line runs right up the right side in front of the head, clipped to the water pump just like the original and into the fuel pump.

I know for certain it is not ignition or the carb.  That carb was bone dry!  While I was suspicious of the fuel pump, I am suspicious this is the problem, especially considering this is the third one in 10 years, with 6,000 miles TOTAL since then.  That averages less than 2,000 miles per fuel pump!  Plus, if the fuel pump was the problem, why would it auto-correct after sitting for so long? 

I am going to try Jon's suggestion of the marvel mystery oil and tetra ethyl lead.  If it does it again, I know something is funny with the fuel pump.

Again, I know the permanent fix is the electric fuel pump, but I am more on a detective hunt to find out what the heck is going on!

Matt

[Scot Minesinger]

Matt,

Not seen too many cars with return fuel line back to tank vapor lock.  However there are numerous posts about a/c cars starting hard as described in my first post on this.  After it sits for 20 minutes in over 70'F weather try running it at 1,500 rpm with foot on gas for 20 seconds and see if that does not make it go away.  Then of course try the Marvel Mystery oil - nothing to loose. 

Not a big fan of the electric fuel pump because it has to be manually turned on and off (of course interlock with ignition so it cannot operate when car is off).  If you add the pump now it is a car that can only be operated effectively by owner.  I could see the electric fuel pump if you had a non-a/c car.

Either way good luck.  I may try the Marvel Mystery oil myself in the gas tank.   

[m-mman]

When considering fuel pump problems remember the enemy is time, not necessarily mileage.

They have 'rubber' diaphragms that are exposed to caustic fluids. (The check valves are also 'rubber' based) Likely you have not used your car daily so the rubber can harden over time where it might not fail if it were being flexed periodically.

Compare them to another rubber automotive part - tires - I am sure you are aware of the pressure to replace tires solely on time and no longer on tread depth. . . Also think about parked tires that develop flat spots from just sitting. It ain't always mileage that causes the destruction.

[Jeff Rosansky CLC #28373]

You can use auto fuel in some airplanes.  If you get vapor lock, you need to switch tanks to allow the lines to purge. 
I wonder if you have a blockage in your return line.  Not much goes thru there so it is possible that dirt/debris over the years have plugged that line.  Maybe check it t see if it is clear and the front/rear rubber hoses are not blocked.
Jeff

[n2caddies]

Not to beat a dead horse. I replaced 2 airtex fuel pumps on my 60 sedan within a few months. One of my Cadillac  vender buddies that deals with them said they had problems with the ones made in Mexico. Rubber quality issues. I went to Oreillys auto parts and bought one made by Bosch and the problem was solved. For as cheap as they are and relatively easy to install I would give the fuel pump one more try with a good new one before I messed around with a electric fuel pump. Incidentally both of my 60s where AC cars.
Randy

[Glen]

To verify if it is vapor lock try cooling the fuel pump with water while the “vapor lock” is occurring.  If it fixes the problem then it is vapor lock.  Otherwise you need to look elsewhere. 

[Dave Burke]

Hi Matt,

What Glen said - basically I keep bottled water in my trunk in the summertime.  I have also sheathed my fuel lines in that heat reflective tape you can get at an auto store.  One of the tricks that I have been using is to let the car idle for a few seconds when I have let it sit for a while on a hot day (say for instance, I am at the grocery store).  If I am not careful, I have the same trouble with my '57 as you describe.  But I have also figured out that if I rev the engine a bit at idle, I suck the vapor into the carb and that draws fuel as well.  Furthermore, in a week or two , I am going to drop my fuel tank, double-check and seal the metal fuel line connections, and change the fuel strainer sock (it has probably never been done).  If it is as clogged as the oil pick-up on the oil pump was, then that would restrict fuel flow a little and that is not helpful.  I have tried the additive route too - it works.  Generally though, I rev the motor until the cooler fuel from the tank makes it past the pump, and then at my first opportunity I mash the gas pedal a little to make sure that she has drawn the cooler stuff in.  Finally, in the summer, I use distilled water as a coolant (and Alabama gets hot)!

Good luck and happy motoring!

Dave Burke
CLC# 27968 

[Joe V]

Excellent advise from all so I will only say that, from my experience, you are not even close to solving a fuel problem until you get a mouthful of gas.  So the good news is you are on the down side of the problem curve and a solution will follow shortly.

[Jon S]

Excellent advise from all so I will only say that, from my experience, you are not even close to solving a fuel problem until you get a mouthful of gas.  So the good news is you are on the down side of the problem curve and a solution will follow shortly.

Obviously, you missed a lot of the information provided. . .

[47bigcadillac]

A gas tank full of winter gasoline will cause these issues when it gets warm in spring

http://oilprice.com/Energy/Gas-Prices/The-Reason-for-the-Fall-in-Gas-Prices.html

[35-709]

You can use auto fuel in some airplanes.  If you get vapor lock, you need to switch tanks to allow the lines to purge. 
I wonder if you have a blockage in your return line.  Not much goes thru there so it is possible that dirt/debris over the years have plugged that line.  Maybe check it t see if it is clear and the front/rear rubber hoses are not blocked.
Jeff

To clarify, while you can use auto fuel in some aircraft engines that are properly STC'd,  it MUST be the non-ethanol variety such as found at many marinas and some gas stations.  It is absolutely against FAA regulations to introduce ethanol/ethanol laced gasoline into any gasoline powered aircraft fuel system.

You can also buy auto fuel at some airports for those aircraft allowed to use it, but you may be certain that does not have ethanol added.  Some cautious pilots carry an ethanol checker to be sure the airport auto gas hasn't been tainted with ethanol gasoline by mistake.