Packard Forum Index » Pre-War (1899-1942)

Owen D-excellent analysis, as usual. I worked with an outstanding mechanic who insisted that "vapor lock" is an old wives tale, a country bumpkin excuse for what can be explained by those with proper theoretical knowledge. I'm inclined to agree. I can not fathom that the auto manufacturers of the 1930s, with their vast engineering staffs and state of the art engineering labs would not be able to detect or fix "vapor lock". you always heard about early Ford V8s suffering from it, If you look at their engineering (if that's what you want to call it) the fuel system was made to heat warp due to the placement of the pump. GM, Chrysler and Packard had large engineering labs and lots of smart guys on staff, they would have discovered the cure for the dreaded "Vapor lock".
It all starts and ends with the mechanical fuel pump, the two halves must be flat to each other, and after 70 years and generations of gas station monkeys reefing on the screws to tighten them, this usually isn't the case. The diaphragm has to be able to handle the stuff they are calling gasoline these days. Then all of the other items you list have to be correct.

John, excellent point about the distortion of the mating faces on a fuel pump; it's a step quality rebuilders take and we often overlook in home-rebuilds.

One other thing I think worth mentioning is some fuel pumps were fitted with an expansion chamber on the outlet side of the pump. I do not know what problem the chamber was trying to cure, but these chambers were a common item. I don't know if they were on Carter and AC pumps or just one of them. Neither of my Packards ('37 Six and '47 Custom Clipper) have one; although, the pump on the 47 has a place that can be drilled and tapped to fit one. I will probably add it when I have the pump off for inspection.

Same purpose as the big round dome on the piston pump of the Ahrens-Fox fire engines, to reduce the pulsations to a more uniform flow. Used on all the prewar seniors up thru 1939.

Nothing to do with mitigating vapor lock, que no?

No such thing. Old wives tale.

Interestingly, there is a companion thread on Vapor Lock on the SDC forum. Saw mentioned there and have seen it elsewhere numerous times that 1 gallon of diesel fuel to 20 gallons of gas will work well. Since until just recently I have not encountered the problem for several years, I used to add 8 oz. of Marvel Mystery Oil to a tank of gas as that is also seen recommended many times. After several years with no problem, now it's occurred on three of my cars and one is a V-8. The last occurence was on an inline six and when I lifted the hood, the inlet bowl filter gas was bubbling.

The only experiences I've had so far with vapor lock were all on inline-6 engines with small carbs. Ford 200's, 250's, 232's, and Dodge 225. Mostly 60's through 80's cars. I did notice once on a 1980 Volare that the factory contrived some sort of heat shield system surrounding the carb. Looked like it made things tough to work on though.

I recall seeing small electric fans directed towards the carburetor on early 1970s Datsuns. I believe this method was used by other makes too.

Then why on the 32 900s, Packard reversed the front most right side louver vent to open in the opposite direction of the other vents to direct air to the fuel pump. I thought it was a change done by a previous owner(s), but the current owner claimed that that was factory correct.