[Reatta Man]

Tom,

In hot weather, underhood temps can easily run 300 degrees.

Joe

[Tom400CFI]

I know it. Due to exhaust heat coming off the manifolds/cats, etc. However, the FUEL will never reach that temp in the fuel rail...which is why I said:

Originally Posted by Tom400CFI

This is the WORST case. I would like to see fuel temp measured, leaving the regulator back to tank, that measures 266*F. I don't think you can create that situation with out out-side heat sources added.

And even if you did measure those temps, that is WORST case fuel. So MAYBE on a 104*F day, you also happen to get the crappiest gasoline ever. But I doubt it. Again, in my 20+ years as a mechanic, and maint. fleet manager of over 100 vehicles....I've never seen it happen. It's always something else that is actually, scientifically explainable.

[Pbruneau]

Yes, In 2007 my I experienced what I thought was vapor lock on a very hot day in my 1980 spitfire, stranded at the side of the road, this was the first time, I have owned the car since 2005. I had the car checked out and there was nothing found wrong with the car. I have experienced the same thing three times this summer, the third time was yesterday.

[D Yaros]

Yes. - For the first time ever. Using MI gas, not my usual WI petrol
No.

[DeSoto Frank]

My personal experience, based on 25 years of driving, most of which has been in carbureted vehicles that were pre-1970, ranging from 1941 De Soto through '48 Chrysler NYer, '51 & '54 Chevy trucks, '55 De Soto, '60 Chrysler Windsor, '61 Plymouth Belvedere, '61 Rambler, '62 & '65 Falcons, '64 Valiant, '66 Chevy Impalas, and a few others. All had stock mechanical fuel pumps.

I have never experienced "vapor lock".

Any fuel starvation issues were related to blocked / perforated tank-to-pump lines, clogged strainers in the tank (rust/gum), bad fuel pump, blocked vent in gas cap. Most fuel-pump failures I have experienced were at least 15 years ago, and involved leakage, not fuel starvation.

That said, I HAVE encountered many instances of PERCOLATION, which usually happens when you park the vehicle, and heat from the engine causes fuel in the carb bowl to boil, forcing it into the intake manifold either through the carb jets or through the bowl vent tube.
Some carburetor mfrs began installing "anti-perc valves", which opened when the throttle was in the closed position, allowing the fuel to boil-off without flooding the engine.

So, with percolation occuring, one of two scenarios occurs: intake floods, and / or carb bowl goes dry. In either case the car is difficult to start when you come back to it.

Percolation seems to be much more prevalent with down-draft carbs.

I did have frequent trouble starting the '51 & '54 Chevy trucks when hot, as the starter tended to crank the engine a lot slower when things were hot. (Exacerbating the percolation problem)

I have noticed that carbs tend to go dry when sitting a lot quicker than 20 years ago. If I leave a carbureted vehicle sit for more than two days, I can expect the carb to be totally dry when I come back to it, and require 15-20 seconds of cranking to get it started. I usually give it a shot of starting fluid, to save the battery /starter.

I have never had to do the "tin foil" or "clothes-pins on the fuel line" tricks.

( I have also never had a flatty Ford V-8... )


From what I've read about modern fuels / fuel injection systems / fluid mechanics, it should be unlikely for fuel to flash into vapor in a modern F-I system since the fuel is pushed from the tank, but that assumes everything is working properly.

Most issues from modern "ethanated" gasolines in old cars seem to come from the alcohol attacking rubber parts in the system: hoses, diaphragms, etc.

Not looking to start / magnify any fist-fights; just citing my own experiences over the years.

Regards,

De Soto Frank

[carbking]

Vapor lock can be an issue with carbureted engines; ALTHOUGH TRUE VAPOR LOCK IS QUITE RARE!

Desoto Frank's post about percolation is excellent; and virtually all of the issues we have seen that were diagnosed as vapor lock turned out to be percolation.

As to fuel injected vehicles. I cannot imagine any way that vapor lock can occur (some have mentioned the boiling point of ethanol, but neglected to remember that the boiling point changes significantly under 45 psi).

However, the myriad of electrical sensors, solenoids, switches, printed circuit boards, gizmos, whatchamacallits, etc. which permeate the modern vehicle are ALL subject to misfunction at higher temperatures.

My GUESS would be that "vapor lock" on an EFI vehicle would actually be an electrical failure.

Jon.

[Fr Mike]

Here's some more antique car experience with vapor-lock, for whatever it's worth:

I have a 1931 Model 8-57 Buick and a 1936 Plymouth P2, both cars unmodified original stock.

In Wisconsin, the summers get up into the 80's and 90's, with high humidity.

The Buick has characteristically been vapor-locking frequently (most gas available around here is stated to contain up to 10% ethanol). So, this summer, I installed a gear-driven, push type, electric fuel pump that can pump alcohol . The pump is designed to maintain 2 1/2 lbs. pressure (for my car), and to increase the liquid volume when vaporization takes place. So far, no vapor-lock!

On the other hand, the Plymouth, which is my driver, has never vapor-locked, even when touring in the 90's on black top back roads. It runs reliably with its unmodified stock mechanical fuel pump.

Interesting!

[old car fan]

I do not think vaper lock is a problem,something else is not right.Not buying the vaper lock

[jaxops]

Yes.
Yes.

In 2007 I had to use heat shielding material on the 56 Cadillac to protect my exposed fuel lines and fuel pump from manifold heat. My fuel in the fuel filter boiled regularly. This heat-wrap solved that problem although it looks ridiculous.

In 2009, with Ethanol required by Virginia throughout the year not just in Winter, my engine temperature has been up at least 20 degrees, running at halfway instead of below half (probably about 200 degrees F or so). This is also true for my 90 Mercury, 70 Electra, and my 56 Cadillac, as well as my wife's 2001 MB. The difference is that the newer cars have return lines and the fuel doesn't sit in he line getting hotter. After an hour's drive on the expressway, I could not restart the 56 Cadillac last Saturday. It was a warm day but not really hot.

[carbking]

For those of you having difficulty restarting a hot engine, try the tip from our "troubleshooting" page:

THE CARBURETOR SHOP / Troubleshooting

This particular issue IS certainly related to the fuel, but it IS NOT vapor lock.

Jon.