Packard Forum Index » Post-War (1946-54)

To add one more recent anecdote about vapor lock:

Last month I had occasion to drive my 55 Pat from Pahrump to Las Vegas, NV in 100F+ ambient heat. I went in the morning and returned in the late afternoon and drove around Las Vegas traffic off/on during the day on a series of errands.

My 55 Pat has stock fuel system except for the addition of an inexpensive NAPA pulse-type fuel pump mounted in the inlet line below the driver door.

100F+ ambient in Las Vegas stop/go traffic means 120F+ air temp at grille inlet. When caught in this type traffic, my Pat was right on the verge of vapor lock as evidenced by stumble and minor/quick cutout of power. Once moving, even in this traffic, the vapor lock did not manifest itself.

On the way back to Pahrump in the late afternoon with ambient temp still over 100F, my Pat was able to pull the long grade from I-15 (2200ft elevation) to Spring Mountain pass (5400ft) without a whimper. Of course this was at 55-65mph with attendant airflow.

I knew from previous experience that without the electric pusher pump (~3-4psi) my Pat would have vapor locked.

Craig

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You're spot-on and maybe I'll just try the steps in stages, starting with the re-introduction of the electric pump. Although the latest extreme conditions will soon give way to those of a more normal nature. Of course, It's like going to the Dentist and your tooth stops hurting when you go in to the office

bhappy -

I respectfully disagree with your proposed rerouting of fuel through a rubber hose from the electric pump, back by the tank, all the way up to the carb.

Standard fuel hose doesn't last very long with these new fuels. Fuel injection hose or SAE 30R9 will, but would be rather costly over such a long run. Hose is really only needed at those points where flexing is known to occur.

If your thought is that rubber would insulate the fuel against heat, then why not get the cheapest fuel hose you can find that would fit over the steel tubing, slit it along its full length and slip it over the fuel line.

Of course, be sure the existing steel fuel line is free of leaks and properly routed, along the outside of the frame rail - replace as required.

These cases of verifiable vapor lock are really interesting.

Obviously the Packard company was able produce problems at the proving grounds because they started putting heat shields around the fuel pump and carburetor.

That one about the filter bowl has me scratching my head because if the motor is starving for fuel then there should be no pressure in the line unless the float is stuck closed. Perhaps the water splashing on the fuel pump released a stuck valve.

Packard cited vapor lock as a cause of poor performance but said nothing further about how to service the problem except for updraft carburetors where they said vapor locking occurs in an idling motor.

One of my suspicions is that there is simply a problem with these old fuel pumps. Maybe the valves don't work right because the castings are getting old and creating problems. They are after all just cheap zinc pot metal. Years ago people were putting electric fuel pumps on cars because they couldn't get parts for the mechanical pump. I remember one Caddy 12 that had the fuel pump gutted and was running on one of those fantastic Stewart-Warner electric pumps. It never broke down so maybe these cars should just be running all electric with a dummy mechanical pump.

Suppose for example that the pump is creating suction internally because of the valves. This reduced pressure will cause gas to boil.

Another possibility is that a restriction in the supply line is causing a low side vacuum. Once I dealt with a Clipper that acted like vapor lock. You could turn the electric pump on and the thing would still be starving for gas at full throttle. The location was terrible so I redid the whole thing and put a Hirsch Airtex unit midway in the line at the lowest point. That fixed it.

The postwar cars are designed to create a syphon action that keeps the fuel pump full when parked. If a filter or fuel pump is higher than the lowest point in the fuel line then that could create a low pressure point where gas boils.

Craig, BH and Tim, I am still mulling around all of the advice and experiences before I act.

While both of my Packards experienced vapor lock that day of the parade, it seemed to happen after running for more than 30 mins and stopping for awhile. On the way home my wife was driving the '50 and I was in the '56. The '50 stalled after sitting at a light and entering the freeway. I stopped with her and shuut down the '56. I left to go home to get tools and the '56 stalled within a mile. Try calling a tow company saying you've got TWO PACKARDS (both green) STUCK ON THE FREEWAY A MILE APART DURING A FIRE STORM! That was for naught because both cars soon cooled and we made it home.

Yesterday we drove the '50 about 30 miles and stopped the car for about 10 mins. and it stalled right away. About 3 hrs. later we went home, stopping half way for lunch. It stalled again right after the start. Let it cool down and we were off like a prom dress at 2 AM!.

bhappy -

Glad to hear that you haven't jumped to any conclusions. Otherwise, you run the risk of throwing the baby out with the bathwater.

WRT your '50, have you verified that your carb has an insulator sandwiched between two base gaskets and that the fuel pump has the insulating bushings and heat shield (and insulating washers)?

To illustrate the importance of insulators, the V8 Packards never came with a fuel pump shield, but I once solved an owner's chronic fuel/heat problem by having him make his own carb insulator from a thin piece of phenolic board. It took some convincing to get him to try that, but it worked.

I should also mention that, instead of placing rubber hose over the steel fuel line, there is tape, wrap, and even sleeve material available for insulating fuel lines. Most commonly found in performance catalogs. The dual quad set-up on '56 Caribbean used a sleeve type on the feed lines from the filter to carbs.

I, too, wonder if the mechanical fuel pump is in need of rebuilding (a fairly easy job for the DIYer) or replacement.

A good scientist manipulates only one varible at a time in his experiments; as inconvenient as that sounds, I hope you take the same approach. Insulating the entire fuel line is the last thing that I'd try.

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BH - Growing up watching my father fix cars, that is one thing that I learned and how quickly I had forgotten in my haste to get my cars fixed. Now that I'm retired (not just tired anymore) I can take my sweet time and methodically complete each fix. Thanks for the shot in the arm.

I hadn't thought about carb / fuel pump insulation. just focused on the metal fuel lines. Like you stated, one thing at a time.

Bob - I'm having the same vapor locking issues with my 51 in this heat. I've added some NOS asbestos spacers under the carb in lieu of the phenolic spacer. The car has the stock issue shield over the fuel pump, with the correct phenolic tubes around the pump bolts. I installed a longer lenght steel tube from the fuel pump so that I could bend it over a few inches in order to keep the fuel line from being directly over the manifolds.

I think my next modification will be to install a larger fan - the 51 tech sessions recommended a larger 19 7/8" diameter fan rather than the stock 18" for 327 engines. My 288 has the 18" fan, but the engine has been modified with 327 rods, crank etc and bored out .080 so the displacement is closer to about 340 ci. These modifications have caused the engine to run hotter even with the new core in the radiator. I'll let you know how the new fan works. Probably will rebuild the fuel pump as well.

TRy driving with hood removed. If it solves the problem then think about obtaining a second hood and modified with louvers or hood scoops.

Keith, are buying bad moon again?