Vapor Lock Fuel Choices

[Florian W.]

I know this topic has been beaten to death, but I haven't found any other post that answers my specific question.

My '60 Fuelie is stock other than 1/2 point lower compression ratio and a fuel shutoff solenoid under the plenum next to the fuel distribution spider. The new radiator easily controls coolant temp and the various component temps seem to be in line with what others reported with their IR gun readings. Running the only fuel available around here in central California (pump gas with 10% ethanol), the vapor lock is terrible.

I've read that others have had some luck with av gas or "race" fuel and I've decided to try something along those lines. I haven't had much luck with the tech guys at VP Fuel as they don't seem to get many requests to fix this type of issue. In a perfect world, they would list the Vapor Lock Index, Vapor-Liquid Ratio and Fuel Distillation Profiles in the spec sheets of their 26 fuel choices such that we could make an informed choice. What they give us is the Reid Vapor Pressure number and the the temperatures of 3 points on the distillation curve (10, 50 and 90%), which is better than nothing, I suppose.

With what little I know, I would think we want significantly higher temps along the Front end of the distillation curve - the 10 and 50% points. These are the temps at which a certain percentage of the fuel will evaporate at specific conditions. Typical temps are 145 for 10% evaporation and 210 for 50%. Many of their fuels are little different than pump gas in this respect. For example, their very popular VP101 and VP110 have 10 and 50% temperatures that are very similar to the summer blend pump gas in California (their temps are much better than the winter blend, however). And, in trying the VP101, the vapor lock was reduced over winter blend pump gas, but was still there.

In my third attempt at talking to someone at VP's tech line, I was given a different option. He said that one of their fuels, C10, was now used primarily by the military for drones as they were having vapor lock issues due to altitude and temperature. At 212, the 10% temperature is much higher than most anything else they offer.

If you're still with me, I'm finally getting to my question: The VP guy recommends mixing this C10 50/50 with pump gas in order to shift the temp of the distillation curve up such that the fuel no longer turns to vapor in the fuel system. That assumes that first the fuels would mix in a homogeneous mixture, and that the overall properties would change roughly based on the proportion of the individual fuel's volumes. He claims this is how fuel blending works, but I'm having trouble believing that it is this simple. I would think that the lighter factions of the pump gas that were evaporating at about 10% at 145 in the straight pump gas would still evaporate in the blended fuel at the same temp, there would just be less of it in a given volume.

Any chemists or petroleum engineers out there that want to weigh in on this? Or how about just regular guys that have already figured this out - that would be even better.

Thanks,

[Domenic T.]

Re: Vapor Lock Fuel Choices

Lee,
I think you will only get the chemist & petrolium guys to weigh in on this. Some of the regular guys are very content with their method of handling this problem & will only get a post bashing.

DOM

[Michael W.]

Re: Vapor Lock Fuel Choices

Perhaps a more complete description of what's going wrong with your car might help. The term 'vapour lock' is quite often misapplied.

[Dan H.]

Re: Vapor Lock Fuel Choices

My friend's 57 FI would boil the fuel in the float bowl, neat gurgling sound, due to the absense of the fuel gasket under the plenum. Put one on, problem solved! He just runs good ole Ca. gas, no snake oil. Try to keep it simple, then you can fill up anywhere. Try the full gasket to see if you can get away with a quick fix.
Dan

[Michael W.]

Re: Vapor Lock Fuel Choices

My friend's 57 FI would boil the fuel in the float bowl, neat gurgling sound, due to the absense of the fuel gasket under the plenum. Put one on, problem solved! He just runs good ole Ca. gas, no snake oil. Try to keep it simple, then you can fill up anywhere. Try the full gasket to see if you can get away with a quick fix.
Dan

That's percolation, not vapour lock.

[Florian W.]

Re: Vapor Lock Fuel Choices

Perhaps a more complete description of what's going wrong with your car might help. The term 'vapour lock' is quite often misapplied.

The symptoms are very typical of most hot fuel handling problems: Vapor forming in the lines preventing liquid fuel flow. It's apparent after trying to restart after a hot shutdown or idling for any length of time once the engine is hot. The fix is either to wait until it cools enough that the gas is liquid again for a restart, or in the case of running problems, to increase engine speed. With higher fuel flows, the fuel doesn't spend enough time in the hot lines to vaporize, so it runs fine at moderate to high speeds, regardless of the fuel or outside temp.

[Jim L.]

Re: Vapor Lock Fuel Choices

The symptoms are very typical of most hot fuel handling problems: Vapor forming in the lines preventing liquid fuel flow. It's apparent after trying to restart after a hot shutdown or idling for any length of time once the engine is hot. The fix is either to wait until it cools enough that the gas is liquid again for a restart, or in the case of running problems, to increase engine speed. With higher fuel flows, the fuel doesn't spend enough time in the hot lines to vaporize, so it runs fine at moderate to high speeds, regardless of the fuel or outside temp.

There are some things you can do to mitigate the unpleasant effects of fuel percolation:

1. When you stop your car, open the hood. Let the hot air escape

2. To start a hot FI engine, hold the throttle wide open while you crank. Engine will start immediately. It might run like crap, but it will start. And that brings me to:

3. Once the engine is started, don't try to play with the throttle to get it to smooth out. That takes too long. Instead, start driving. That raises the system fuel pressure above the vapor pressure of the fuel and percolation stops..... instantly, like flipping a switch.

4. Practice situational avoidance: Don't do parades. Don't get caught in stop and go traffic. Don't try to drive in warm weather with left over winter fuel.

None of my suggestions, either separately or taken together, solve the percolation problem. But they do make it easier to tolerate.

Good luck,

Jim

[Timothy B.]

Re: Vapor Lock Fuel Choices

Florian,

I also wanted to add if the engine does not have a vacuum advance you could try to re-curve the distributor to allow more initial timing. Get it up to around 18* and may cool the engine some.

[Florian W.]

Re: Vapor Lock Fuel Choices

Thanks for the suggestions, Jim and Timothy. Since I've been researching other posts on this, I've already tried many items you've listed. I always pop the hood when stopped, and I've even tried driving with it unlatched. I've advanced the timing as well, without much affect. Although the coolant temp is well controlled at 170 to 180, I've even thought that I might gain some additional heat rejection from the intake area by replacing the thermostatically controlled clutch fan with a clutchless unit. And while I do try to avoid vapor lock situations, there have been occasions where I'm stuck in traffic or have to restart it after a short heat soak. The unusually warm winter we've had combined with the winter blend fuel has made the situation so bad that there have been times lately when it won't even begin to start until it sits for 20 minutes with the hood up.

[Jim L.]

Re: Vapor Lock Fuel Choices

The unusually warm winter we've had combined with the winter blend fuel has made the situation so bad that there have been times lately when it won't even begin to start until it sits for 20 minutes with the hood up.

I don't know what to make of the no-start issue. I've never, ever had an issue getting a fuelie to start when hot. Mine always start, even with winter fuel on a decidedly non-winter-ish day.

But speaking of winter fuel, with it in the tank I've experienced fuel perc at ambient temps as low as 65 - 70 degrees. Preliminary investigation revealed that the spider line temps were around 100 - 105 degrees at the onset of perc. Thankfully, we seem to be getting summer blend now in the Sierra and percolation won't be an issue again until the days warm considerably.

I'm going to back pedal slightly regarding that no-start problem.... now that I think about it, I did see that once a long time ago. The problem was that the anti-siphon mechanism had failed and fuel was dribbling into the engine causing it to be horribly flooded. When cold it started at the first turn of the key, though..... NOT a good thing!

Jim

[John D.]

Re: Vapor Lock Fuel Choices

Florian, If your '60 has a repro fuel line that runs from the engine fuel pump to the fuel filter then you have a problem. It seems that no one (that I know of )reproduces a '59 to '61 and or '62 FI fuel line that has the correct bends and configuration as original.
I have mentioned this before here.
One of the members of the Pittsburgh Tri-State chapter has owned his '60 FI car since '63 or '64. Last year he brought his car to a judging seminar. Parked next to his '60 was another '59 or '60 FI car. I called everyone over to the two cars to point the difference between the original line and the repro line. Light night and day.
The repro is hugging the valve cover and at one point close to the firewall it is almost touching the valve cover.
I have seen repro lines on '59 to 62's that are touching the front of the cylinder head/valve cover.
Solution is to massage your original line or have another one made. Then insulate this fuel line also. The gas may be boiling before it even hits the FI unit.
John

[Florian W.]

Re: Vapor Lock Fuel Choices

John,

It has the original line that really isn't close to touching anywhere. But you are right about it picking up heat. I was surprised by its temperature enough to wrap it in an easily removable insulation sleeve. Unfortunately, there was little improvement. Too many other places to pick up heat, I suppose.

Thanks

[Duke W.]

Re: Vapor Lock Fuel Choices

Your problem is most likely percolation due to the reduction in the midrange boiling points from the addition of ethanol, which boils at 170F. The problem is the 20-40 percent range, which is fairly flat, and the 40 percent point is only 150 degrees F. Then it starts to climb.

The problem can usually be eliminated by using racegas or avgas, but that's an expensive and often inconvenient solution. All vintage cars with non-pressurized fuel supply systems are suffering fuel perolation problems to some degree.

In the last year there was an extensive thread with temperature measurements at various points in the fuel system both before and after the installation of insulation. The fuel temperature is already very hot before entering the fuel pump due to the pipe's proximity to the exhaust manifold and the low flow rate at idle and low load.

Search for this thread and also the link to the Chevron Motor Gasoline Technical Review pdf.

I think most owners have mitigated the problem sufficiently with insulation and changes in driving habits to live with current commercial mogas.

Duke

[Joe R.]

Re: Vapor Lock Fuel Choices

In the last year there was an extensive thread with temperature measurements at various points in the fuel system both before and after the installation of insulation. The fuel temperature is already very hot before entering the fuel pump due to the pipe's proximity to the exhaust manifold and the low flow rate at idle and low load.
Duke

Duke,

Is this the thread you're thinking of?

https://www.forums.ncrs.org/showthread.php?100292-L84-fuel-system

Joe

[Florian W.]

Re: Vapor Lock Fuel Choices

Thanks, Duke. I did read the earlier thread and the Chevron pdf. In fact, I sent the Chevron tech folks an email asking about the outcome of blending fuels with very different distillation curves (I'll be surprised if they answer). So many of the components (pump. lines, filter, spider, solenoid, nozzles, etc.) are so close to the 150 degree temp where a significant portion of the pump gas will turn to vapor that I wonder if I could ever insulate enough to make a big difference. Wrapping the fuel line from the pump to the filter didn't seem to do anything by itself in my case.