[OldsDoug]

Yes and yes - just last night, in fact, a friend's '36 Ford.

[jaxops]

Yes. I had gasoline boiling regularly even when going around the block!
[I wrapped my fuel pump and fuel lines to insulate them from the high temperatures on the engine, ad try to avoid additives other than real-lead, and gas that has ethanol]

Not yet, although I am running at higher engine temperatures due to the heat of the summer and probably also the gasoline quality.
Also- my 1990 Mercury went well over the 1/2 way mark on the temp guage twice last week. It has never done that before.

[Dave@Moon]

Originally Posted by joe_padavano

In which case, wouldn't the plugged return line or non-functioning regulator be the actual cause of the problem?

In this incredibly unlikely vapor lock scenario, yes.

[Reatta Man]

More info about the 'impossiblity' of vapor lock in an FI engine:

From Paul Brand's column in the Minneapolis Star-Tribune in 2005:

Hemming and hawing mark return of vapor lock
By Paul Brand

Last update: July 20, 2005

How quickly we forget. Motorists older than about 40 years of age recall the "good ol' days" of summer driving -- driving along in traffic when suddenly the engine starts to buck and sputter. It may stay running with the throttle, but it staggers, runs rough, lacks power and feels like it's right on the edge of stalling. Or, you've parked the fully warmed-up vehicle for five or 10 minutes, then find it won't restart easily. It cranks and cranks and cranks, and finally begins to pop and cough. You get it started, but it continues to sputter and shake for 30 seconds to a minute before it clears up and smooths out and you drive away.

Younger motorists with newer cars aren't used to experiencing these summer driving characteristics, so when it occurs, they immediately think something major has gone wrong. They write this column or call my radio show, asking for advice and hoping the problem isn't expensive to fix.

OK, have you zeroed in on what I've described? Vapor lock, that under-hood demon from decades ago, is back, often with a vengeance. Vapor lock is nothing more than premature fuel vaporization. Under-hood heat actually is boiling the fuel in the fuel rail near the injectors, aerating the fuel with gaseous bubbles, dropping fuel pressure, and making the injectors spit and sputter raw fuel into the combustion chambers. No wonder the engine runs so badly or even stalls.

Vapor lock is a function of high outside ambient temperatures, extreme under-hood temperatures and the volatility of today's gasoline. This recipe is compounded by the higher volatility of our ethanol-enriched gasoline.

So, if your vehicle begins to exhibit the run-rough, lose-power, I'm-about-to-stall-and-leave-you-stranded symptoms, what can you do? Try different brands of fuel, perhaps even a tank of non-oxygenated, to see whether the change in fuel makes a difference. Service the cooling system and clean the engine to reduce operating and underhood temperatures. And if you know you're going to be stopped only for a few minutes before needing to restart the engine, open the hood and let the engine idle for a minute or so before shutting it down to carry as much combustion heat out of the engine and into the radiator, and then allow it to dissipate into the air from the open engine compartment. If this helps the restart scenario, you know vapor lock is the culprit.

Paul Brand: Hemming and hawing mark return of vapor lock

From the Car Talk Web site, operated by PBS:

Q:Hi, I have a 1995 Nissan Quest. My question is when I am idling in heat/(90+)/humid/weather my car cuts off. After about 15-20 minutes my car will start back up. Is this a vapor lock problem in the gas tank as the last time it happened I could hear the fuel pump. Is there a solution for this problem as I moved to Texas last year and will be living in HOT weather this summer. I love my van and don't want to have to buy a new vehicle if this problem is fixable. Thanks!

A #1 by 'Tester':Contrary to what most people believe, vapor lock can and does occur on fuel injected engines.

A fuel injection system is a closed loop system. This means whatever fuel isn't used at the fuel injectors is returned back into the gas tank. This returned fuel has been subjected to the heat the fuel rails absorb from sitting above the engine. So the fuel begins to act as a coolant and returns this heated fuel back into the gas tank. If conditions are right, this returned fuel can begin to heat up the fuel in the gas tank. The more heated gasoline becomes, the more volotile it becomes. So eventually the fuel becomes volotile enough where underhood temperatures cause the fuel to boil. Or vapor lock. This is more of a problem if the fuel contains any ethanol.

If vapor lock is occuring, it usually means underhood temperatures are too high. And one of the first things to check is the cooling system. If the cooling system is no longer able to efficiantly remove heat from the engine, the underhood temperatures go up.

A#2 by 'Greasy Jack'
The effect Tester describes is especially true when exacerbated by an ethanol blend in the fuel, which most states have these days during at least part of the year. Ethanol turns to vapor at a lower temperature than regular gasoline and so is more suceptable to vapor locking. That said, the reason why a fuel injected car shouldn't vapor lock is because the fuel should be under enough pressure that the pressure itself stops it from vaporizing in the lines, sort of like how your pressurized coolant system prevents the coolant from boiling. If your fuel pressure is low due to a clogged fuel filter or a weak fuel pump, this will also make your van much more suceptable to vapor locking. This might be the first indication of a fuel pump on its way out.
Car Talk - Vapor lock problem?

From the E85 Web site:
Q: Does ethanol cause vapor lock on hot days?
A: Today, fuel vapor pressure is regulated by the EPA with a lower vapor pressure for summer grades of fuel. In the Midwest, ethanol fuel may carry a one pound higher vapor pressure than conventional gasoline. Occasionally, a vehicle may vapor lock on a hot day, but this problem has mostly been eliminated.

E85 | Ethanol FAQ

So, to all, stop saying it is impossible.

[The Green Dragon]

Vapor-lock. I have never had trouble with that until last year. We still have some stations in Wisconsin that sell regular gas and that's what I use, but we went on a tour in Illinois and all their gas has ethynol in it and I filled the tank. The weather wasn't real hot, low 80's, but every time I came to a stop the engine started missing and sometimes stall. I let the engine cool down a little and then it would be OK for a while. My car is a Peerless with V-8 engine, vacuum tank and carburetor in the valley and it does get hot in there. I insullated the gas lines but it still perc.s with ethynol. When I use regular gas I have no problem however in August I am going on the Heritage Tour in Illinois and will have to use ethynol again.
Does anyone know of any additives that will counter act the ethynol?

[Tom400CFI]

Originally Posted by Reatta Man

Vapor lock, that under-hood demon from decades ago, is back, often with a vengeance. Vapor lock is nothing more than premature fuel vaporization. Under-hood heat actually is boiling the fuel in the fuel rail near the injectors, aerating the fuel with gaseous bubbles, dropping fuel pressure, and making the injectors spit and sputter raw fuel into the combustion chambers.

Nothing in the above paragraph is what I would call "accurate". It is a sensationalism of SOME scientific fact, but as written, is not right.

Originally Posted by Reatta Man

A fuel injection system is a closed loop system. This means whatever fuel isn't used at the fuel injectors is returned back into the gas tank. This returned fuel has been subjected to the heat the fuel rails absorb from sitting above the engine. So the fuel begins to act as a coolant and returns this heated fuel back into the gas tank. If conditions are right, this returned fuel can begin to heat up the fuel in the gas tank. The more heated gasoline becomes, the more volotile it becomes. So eventually the fuel becomes volotile enough where underhood temperatures cause the fuel to boil. Or vapor lock. This is more of a problem if the fuel contains any ethanol.

The above supports MY position that in an EFI vehicle, the fuel is constantly COOLED by it's trips back to the tank...which itself is cooled by airflow over and around it.

Originally Posted by Reatta Man

So, to all, stop saying it is impossible.

You post on a pubic forum, looking for opinions...now you're dictating to us, what we can and can not say?? :crazy:

Someone posted earlier that in a modern EFI system the term "Vapor lock" is frequently mis-applied to other, more basic and reasonably expalinable problems. I agree, completely. Also, your quotes from car talk/new paper "mechanics" are FAR from the first time I've seen or listened to them dole out erroneous information.

[joe_padavano]

Originally Posted by Tom400CFI

Nothing in the above paragraph is what I would call "accurate". It is a sensationalism of SOME scientific fact, but as written, is not right.

Thank you.

I'll ask one more time. Someone PLEASE post the exact physical mechanism that "vapor lock" in a modern EFI system causes. The supposed "boiling" of the ethanol cannot cause the tank-mounted fuel pump to lose prime. Any vapor supposedly generated by this "red-hot" fuel return line will simply be vented to the vapor part of the tank as soon as the returned fuel gets there. Any vapor in the 45psi pressure side of the line will be returned to the tank through the pressure regulator and return line. The vapor cannot increase the pressure in the line above the set point of the regulator unless the regulator or return line is faulty (which would then be the primary cause of the problem).

As for quotes from nameless people who post on the Car Talk website, what qualifications do they have? We don't even know who they are. As I said before, there is a lot of bad information out there that is passed off as "conventional wisdom". Batteries on concrete, deer whistles, hydroplaning causing the cruise control to uncontrollably accelerate the car (yes, EXCEPT for the mid-60s Oldsmobiles with the speedo cable driven from the LH front wheel). Gather all the factual (as opposed to anecdotal) information you can and make your own decision. I frankly don't care what anyone else believes.

I will say the thermally-caused electrical faults in EFI sensors are MUCH more likely to be the source of a suspected "vapor lock" problem. It's just much easier for a mechanic to blame the gasoline than to actually trace down an intermittent and difficult to duplicate electrical problem.

[d2_willys]

Vapor lock: Hmmm, did anyone mention the OCTANE RATING? I have a 53 Merc with original flathead, that purrs like a kitten and runs great, but is prone to vapor lock due to the fuel pump being on top of engine (stupid ford idea). I drove the car back from Boise, Idaho back in 2006 and experienced vapor lock like never before. The car ran great from Boise to Jackson, WY. Then after getting down to I-80, had nothing but problems. Seems the octane there was 85 and the car vapor locked 5 times going east on the interstate. I finally got to Colorado and the outside temperature finally went down into the 80's. The next day it vapor locked again, then I put in some 87 Octane gas (probably without ethanol) and the vapor lock quit all together. Seems the octane rating, the higher it is, the better the vehicle runs and vapor lock is less to happen.

Funny thing, my 57 F-100 did almost the same thing on a hot day in Colorado Springs. I believe the octane rating has alot to due with the vapor lock issues. Ethanol does too.

[Dynaflash8]

My three 1939 Buick's will simply not run on the new Florida gas using the mechanical fuel pump. I am having to take the mechanical fuel pump out of the line and depend strictly on the electric fuel pump. This happens about the time the car gets to operating temperature of 180 and gets worse if the temperature goes any higher. In 46 years of driving this one car, it has never ever had that problem even once. Upon shutting the car down, the gas boils in the fuel pump sedament bowl. It is a sad situation.

[Tom400CFI]

Originally Posted by joe_padavano

Thank you.

I'll ask one more time. Someone PLEASE post the exact physical mechanism that "vapor lock" in a modern EFI system causes. The supposed "boiling" of the ethanol cannot cause the tank-mounted fuel pump to lose prime. Any vapor supposedly generated by this "red-hot" fuel return line will simply be vented to the vapor part of the tank as soon as the returned fuel gets there. Any vapor in the 45psi pressure side of the line will be returned to the tank through the pressure regulator and return line. The vapor cannot increase the pressure in the line above the set point of the regulator unless the regulator or return line is faulty (which would then be the primary cause of the problem).


I will say the thermally-caused electrical faults in EFI sensors are MUCH more likely to be the source of a suspected "vapor lock" problem. It's just much easier for a mechanic to blame the gasoline than to actually trace down an intermittent and difficult to duplicate electrical problem.

Clearly, you "Get it". You won't get an explaination for: "the exact physical mechanism that "vapor lock" in a modern EFI system causes."

Because you are right; any boiling in the fuel rail CAN'T physically cause in increase in pressure; the regulator guarantees that!

And the pump in the tank, pushing WAY more fuel than the engine could possibly need, guarantees that any bubbles created by boiling, gets pushed out fo the fuel rail and back to tank.

A clogged fuel filter causing a "drop in pressure causing boiling" (?) THAT would be...a "clogged fuel filter". Chagne the filter. (BTW, The drivability issue would be due to the low FP, not boiling)

And so on.

Yep...you "get it". Nice to see.

Gasoline boils at 100*F to 400*F, depending on the blend. Using a graph I found online that illustrates boiling point vs. pressure, I took the WORST case scenario for gasoline; gas that boils at 100*F. I used the chart to see what the boiling point would be at 45PSIG. The chart showed 266*F. 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.

-Tom