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

I noticed this morning when I started my car at about 78F, that the glass filter bowl was completely full of gasoline with no bubbling evident, even after the engine ran for several minutes. After driving about 10 miles with the temperature outside in the low 80s F, I stopped and looked at the filter bowl. It was about half full of gasoline. The car was running fine. I drove another 10 miles home and parked in the barn and opened the hood to see that the bowl was half full and the gasoline was bubbling.

After about five minutes, the carburetor begain to leak gas at the throttle shaft.

I expect that when I start the car again this evening, it will fire up and die, then act like it is out of gas.

I think what is happening is that the filter and gas line from the pump to the carburetor are heating up from the radiated exhaust manifold heat and pressuring up enough to push gas past the float needle flooding the motor.

When it's hot, the fuel pump seems to be pumping bubbles instead gasoline, which makes for hard starting. Once it starts, it runs just fine, but the fuel pump does not deliver gasoline as it should when its hot and I am cranking the engine with the starter.

Moving the filter bowl down to the fuel pump outlet might improve things by keeping it cooler. It's connected to the carburetor float bowl, and fully exposed to exhaust manifold heat.

I believe that adding a fuel pump heat shield and replacing the inoperative vacuum advance will improve the situation, but I think it will always be an issue with todays "gasoline" in hot weather.

Make sure the insulator is in place between the carb and the manifold.

Yes, there supposed to be a fuel pump heat shield.

This is what it looks like, and I have this one available if you are interested.

Also, check the routing of the hard fuel line. It should come straight out and then bend towards the pump. So it stays away from the manifold as much as possible and in the airflow path from the fan. Here is an example of the line routing on my '54 motor. I would imagine the '37 routing would be similar.

I ran my '54 in So. Calif in 100F heat without an issue.

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The car is a '37 120 C. I think the fuel pump shield is suppoed to be the slanted type like in the lower picture. I'm going to try making a heat shield for the glass bowl filter out of a bean can. I think I can fit the can over the filter and secure it with a wire tie. I'll glue aluminum foil to it for maximum heat rejection. The fuel line from pump to carb looks like the one in the picture except it is coverd with the woven material. I may try wrapping it in foil also. The line from the pump back to the tank appears to be totally stock and in good shape. It may be possible to make a shield for the carburetor out of a can or a piece of sheet metal. It could be secured to the air horn screws.

John Ulrich has photos of various fuel pump shields he has had reproduced for some prewar models. Overall shapes may be similar but one major difference is the mounting methods and locations.

Amazon has some 1/2 ID tubing shield made just for protecting tubing and wiring from heat sources. It is the sheath type that can be placed over the tubing without removing or disconnecting it.a.co/d/h1IkAms

That heat sheilding for the line from Amazon looks very similar to what I have put on my 37 fuel line and it has stopped my vapour locking. Mine is actually the shielding that is put on cars with headers for the spark plug wires.I do not have the fuel bowl but put an inline filter along the frame.

What's with this "vapor lock" jazz? Inline engines, sixes or eights, do not "vapor lock." Valve-en-bloc V-8 Cadillac/Lasalle, 288-ci Cord Lycoming, and of course Ford/Mercury engines vapor locked because the carb sat in the midst of a heat sink. Carburetors on inline engines do not so suffer.

I've known owners of all the above V-8s who've suffered vapor lock. A Cord friend, bizarre as it sounds, ended his with wooden clothespins. I kid you not.

I've driven straight eight Packards on both coasts for 47 years in all kinds of weather and never, ever experienced vapor lock. Neither has the owner of any inline Packard, Buick or for that matter, Delage D8S we've known ever suffered vapor lock, and it can get stifling here in the greater Bay Area.

Perhaps other issues are being termed "vapor lock?"

Inline engines most certainly do suffer from "vapor lock", flooding, carburetor boilover, etc. It's very common among inline engines with downdraft carburetors and fuel pumps located on the manifold side of the engine, which is most or all of them. The problem is aggravated by many modern "fuel blends" which are not designed for carbureted engines with vented fuel tanks. Flathead Mopars used a fuel pump heat shield, as did many other makes, including Packard. Pontiac 8s used a metal shield under the carburetor base to deflect manifold heat, along with a heat insulator under the carburetor. Packard used special non-metallic bushings on some fuel pump mountings to reduce heat transfer from the engine block to the fuel pump. It's true that V8 engines, especially large 1950s V8s with air conditioning, suffered form heat-related fuel issues, but it was not and is not exclusive to them. Flathead Ford V8s were handicapped by a high-mounted fuel pump, but that was offsedt by the fact theat the exhaust manifolds were located under the block awqay from the pump. Some Lincolns had the fuel pump mounted high on the front of the engine directly behind the fan. They'd vapor lock in hot weather after being parked. "Winter blend" fuels would aggravate heat related fuel system issues in warmer weather, and fuels today can be very problematic in some areas in warm to hot weather.

Quote:Like these?

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I bought a '52 Cadillac convertible years ago. It had a slew of wooden clothes pins on the fuel line to the carburetor. I took 'em off and it still ran. Has anyone ever heard an explanation of how the clothes pin cure is supposed to work?

An old geezer around here used to drive a '48 Plymouth around town. He had "vapor lock" problems in hot weather, which he dealt with by wrapping a tow sack around the fuel pump. He'd pull in a gas station and buy 50 cents worth of gas and tell the attendant to "wet down my tow sack".

It has already been noted how the Ford V8's suffered from this and my Father-in-law was a huge fan of the motor. He ran a garage and he an his customers carried a bottle of Coke in the car and dumped it on the fuel pump to cool it. Guess Coke was cheap and with the bottle capped it was secure until needed! Bet that the sugary mess was a bit much, but hey, they drove the cars and let the rain wash them.
Bob J.