Vapor Lock Poll

[Guest RenegadeV8]

THis is a 2wo question poll.

Are u experienceing vapor lock symptoms THIS year ???

Did u experience vapor lock symptoms during 2007 ??? (2wo years ago)

Of course this assumes that u have been driving your vintage car for at least the last 3hree years.

Also, if u answered this similar poll at PackardInfo.com then your experience has ALREADY been counted.

Sent via DingleBerry® Technology

[Guest RenegadeV8]

no.

no.

Sent via DingleBerry® Technology

[Dave@Moon]

1. I came very close once this year, with an overpowering gas odor at start-up with one tank of gas, but no stalling or failure to start. (This in a Triumph TR6 that never gave me any trouble and has an aftermarket carb heat shield installed just in case.)

2. (As above), no.

[Reatta Man]

Dave,

I had vapor lock with my 2000 Lincoln the other day when the temp here in San Antonio hit 106. Never had that happen on a fuel-injected car before, but a mechanic told me it can even happen to them if it is hot enough. Opened the hood, let it cool off (ha!) and it started in a few minutes. Filled the car with Shell premium (no ethanol stickers on their pumps) and the car has run fine on all of our 100+ degree days since then.

Joe

[ted sweet]

no and no, but i only use gas with no ethanol.

[joe_padavano]

Dave,

I had vapor lock with my 2000 Lincoln the other day when the temp here in San Antonio hit 106. Never had that happen on a fuel-injected car before, but a mechanic told me it can even happen to them if it is hot enough. Opened the hood, let it cool off (ha!) and it started in a few minutes. Filled the car with Shell premium (no ethanol stickers on their pumps) and the car has run fine on all of our 100+ degree days since then.

Joe

Sorry, but until your mechanic or someone else can explain to me how "vapor lock" can overcome the 45 psi pressure from your fuel injection pump (which is mounted inside the gas tank, not under the hood), I think the mechanic was full of it. The pump is immersed in fuel, (unless the tank was empty) so there's no "vapor" on the inlet side. The outlet side of the pump is under 45 psi unless the pump is going bad. Either you car has pressure at the under hood test port or it doesn't. If it does, there's no "vapor lock" and if it doesn't then you have a bad pump.

Edited July 2, 2009 by joe_padavano
Spelling (see edit history)

[Guest Skyking]

No

No

No,

that's with two Metropolitans and a Buick, of course we haven't hit high temps yet, and the way it's been going, we won't.

[Guest simplyconnected]

Sorry, but until your mechanic or someone else can explain to me how "vapor lock" can overcome the 45 psi pressure from your fuel injection pump (which is mounted inside the gas tank, not under the hood), I think the mechanic was full of it...

Joe nailed it. Vapor lock is gasoline that BOILS. Either the barometric pressure must be real low (like in the Rocky Mountains), or extreme heat, or both. EFI engines have positive pressure which raises the boiling point, much the same as a pressure cooker. Most EFI's recirculate, passing any gasses back to the fuel tank.

Old-mechanical fuel pump setups were much more prone to vapor lock because they sucked gasoline fifteen feet, from the tank to the engine. In reality, many cases of so-called 'vapor lock' is nothing more than a loose fuel line connection, a clogged fuel filter, or rust - clogging the gas tank screen.

[Reatta Man]

First. the comment about my mechanic being "full of it" is out of line. He has had a major shop here in SA for more than 20 years, a radio show, is a certified mechanic, is a certified expert witness in state AND federal court on automotive issues and has documented several cases here in South Texas with vapor lock in our record-setting heat this year. You can claim it can't happen, but here in the heat, it is happening. Is the gas 'boiling?' Maybe not, but vapor pressure is possible and present without gas 'boiling.'

Second, you forgot to consider the effects of ethanol. While the boiling point of gas can be as high as 400 degrees, the boiling point of ethanol is 172 degrees. I can assure you, the temp most days around here under the hood of that Lincoln with that V8 under the hood is well over 172 degrees. I've not had any trouble since then while using gas without ethanol, even though it has reached 104-108 in many areas. Some people believe the ethanol content may be way above the 10% that everyone claims they are using.

This rush to call names, jump to conclusions and race to show how much smarter you are than the other guy is getting out of hand, and really spoiling what has until recently been a very enjoyable hobby. It's one thing when several people in here wish to call me names in the forum and in private messages, but to do so to someone you have never met just about reaches the height of arrogance.

One other thing--other car forums agree that it CAN happen, and manage to talk about it without calling anyone names.

Car Talk - Vapor lock problem?

Acura Repair: Vapor Lock code appearing, fuel delivery system, internal combustion engines

Car Talk - "vapor lock" -like symptoms

[keiser31]

Don't really know if it's vapor lock, but my truck will run o.k. for a while and if I stop somewhere, it will be hard to start .

[jrbartlett]

You better check that gasoline again. If San Antonio is an ozone non-attainment area, as Houston is, the stations are required to sell oxygenated gasoline -- which means it does have ethanol in it, whether or not it is premium. Maybe San Antonio is in compliance with ozone standards, in which case you might have a choice.

[Tom400CFI]

I'm sorry, but I agree w/the folks who "called names". No WAY you're going to boil gas in a modern, PFI engine. Even if you had a situation where your fuel rail temp was high enough to boil gas (like during a MAJOR over heating event), as one poster said, the gas is recycled back to the tank at a high rate; the pump pumps WAY more than the engine can use. So at the rate that the pump pumps the fuel through the fuel rails, and back to tank, you'd have to see tank temps nearly as high as the boiling point of gasoline...at 45+ PSI. Anyone see or touched a gas tank near empty after the car has been running on a HOT day? It's MAYBE 110*F. THAT is what is being pumped to and through your fuel rails, and back to tank. I don't see how it could possibly boil.

To answer the poll, No and no. I've never had boiling gasoline in any car, boat, snowmobile, bike or anything, 1910 to now. I don't know who the mechanic in question is, but I am a mechanic and manage maintenance on a fleet of over 100 pieces of equipment. I could be wrong...but so could he. Science, as I know it, says that he is the one who is wrong.

[Guest simplyconnected]

Reatta Man, nobody called you names. We are all car guys with extensive background experience and education, not showmen or braggers.

You mentioned the boiling point of ethanol. Ok, at what pressure? Here's a quote from YOUR resource:

"... 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."

Do you have thousands of cars in Texas, disabled by the side of the road from vapor lock? They all suffer the same heat and use the same fuel. How come all the Flex cars using E-85 still run ok? No, you have isolated instances.

By the way, vapor lock IS boiling; the temperature AND pressure at which a liquid turns into a gas. The physical science of vapor lock is easily proved regardless of what anyone feels about it. There's no mystery and nobody is in denial here, so don't take it so personal.

Carbureted cars with fuel under suction are prone to vapor lock, not EFI systems.

- Dave

[joe_padavano]

One other thing--other car forums agree that it CAN happen, and manage to talk about it without calling anyone names.

Well, since everything on the internet must be true, here's another quote from Wikipedia:

Vapor lock (also known as vapour lock) is a problem that mostly affects gasoline-fueled nternal combustion engines. It occurs when the liquid fuel changes state from liquid to gas while still in the fuel delivery system. This disrupts the operation of the fuel pump...

So I'll say it again. Since the electric fuel pump is in the tank, vapor lock is NOT the problem. Engine-mounted mechanical fuel pumps are subject to vapor lock. The vapor causes the mechanical pump to lose prime. Electric pumps in the tank are covered by fuel and do not heat up and vapor lock. Remote electric fuel pumps on carbuerated cars do not vapor lock either.

Also, since the EFI system has a recirculation system with a pressure regulator in the return side, any pressure above the set point of the regulator causes fuel to be returned to the tank, even if the system is not running. Also, the EFI system turns the pump on for two seconds when the key is first turned to the START position to prime the fuel system and purge any vapor in the system.

Once again, until someone can explain to me the exact mechanism that this supposed "vapor lock" causes in a modern EFI system, I remain unconvinced. Vapor lock specifically refers to fuel vapor prevening the pump from drawing fuel. I fail to see how vapor on the pressure side of the system can prevent the pump from drawing fuel. The links you provided did not explain the physics, only symptoms. Many mechanics also claim that putting a plastic-case car battery on a concrete floor will cause it to discharge (but the same battery apparenly won't discharge when on the metal racks in the store or the metal battery tray in your car). They are also wrong.

Many other temperature-related failure modes exist, and I'm willing to bet that the real problem is a sensor going bad with a thermally-related intermittent problem.

Edited July 5, 2009 by joe_padavano
Spelling (see edit history)

[Dave@Moon]

I fail to see how vapor on the pressure side of the system can prevent the pump from drawing fuel.

I can think of one way. If for some reason the fuel return line was plugged, and the fuel pressure valve was unable to do it's job, then the ultimate pressure inside the line might be overcome with enough heat.

At 45 psi ethanol boils at 208.4 degrees F. However that's typically the pressure with the return line working. Assuming the fuel pump is ultimately able to generate 60 psi into a blocked system (a fairly reasonable limit I would think), that b.p. goes to 224.6 degrees F.

For that to occur, it would have to be hot enough in the engine compartment to make coffee (boil water) in a device strapped to the firewall, not to mention the great clouds of steam generated by driving in the rain. Joe_P is absolutely correct. In practical terms it is simply impossible.

Boiling Point Calculator

Methanol Properties

[Dave@Moon]

One thing I didn't think of when posting the strong fuel smell in my TR6. The tank of gas that was in the car when this occurred was purchased in VERY rural Kentucky about 1/2 way between Louisville and Cincinnati. The last I knew, outside of 3 counties actually abutting Cincinnati northern Kentucky had no oxygenation requirement for it's gasoline. Here in Cincinnati, where all our gas is E10 (10% ethanol), I've haven't noticed a problem in 3 tanks so far this year.

Edited July 4, 2009 by Dave@Moon (see edit history)

[joe_padavano]

I can think of one way. If for some reason the fuel return line was plugged, and the fuel pressure valve was unable to do it's job...

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

[old car fan]

I agree with Ted.He hit it spot on.

[Reatta Man]

James,

San Antonio is an attainment city, but just barely. They have been trying to remain in this EPA category for more than 10 years. If we change categories, we get manditory emmissions testing as part of our state inspection, which drastically raises the price from its' current $14.50 price, and causes several other changes as well.

Several retailers, such as Valero (may still be Diamond Shamrock in some areas) already use ethanol, along with Exxon.

Thanks for the post.

joe

[Jay Wolf]

On the way to The Lebanon TN show was the first time ever my 55 Thunderbird vapor locked in the 5 years I have owned it.

[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]

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.

[Richard Lichtfel]

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]

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.

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.

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]

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]

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

Edited July 7, 2009 by Tom400CFI (see edit history)

[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:

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.

[Guest 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.

[Guest 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

Edited September 14, 2009 by DeSoto Frank (see edit history)

[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.

Edited September 14, 2009 by carbking (see edit history)

[Guest 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!

Edited September 15, 2009 by Fr Mike (see edit history)

[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.