Vapor Lock fallacy?

[Tim Donahoe]

I just did a search on this forum for vapor lock. The reason is this:

Today it was 114 degrees in Redding, CA. By the time I got off work, it was 107. Anyway I drove home 6 miles (three miles on the freeway at 60 MPH). I decided to pull over for gas and, naturally, shut off the engine. I filled the tank, screwed the cap back on and had to go inside to get the receipt. The whole thing took 10 minutes.

When I tried to start the bug (a 1974 DP Super Beetle that has been running fine up until this event), it wouldn't start. I turned the key again and floored the pedal and it started--but ran badly and stalled in a few seconds.

I had heard of vapor lock in situations like this, so I went back inside to buy a bottle of cold water. Went back to the engine and slowly poured cold water all over the fuel pump--and just beneath it. This took a good five minutes. I don't like pouring cold water on a hot engine, so I took my time.

I tried starting the car again and it started but ran a bit rough. I kept giving it a lot more gas than usual and the engine kept running--but I kind of gunned it--just being sure it wouldn't die.

Two blocks later, I downshifted to second on a corner--and the engine didn't die. I made it home and the engine seemed okay, idling on its own before I shut it off.

So ... was there really vapor lock? The fuel pump, rod and flange have not been changed recently, so I know I didn't screw it up. The carb was re-done by Tim at Volkzbitz fairly recently, so I know it wasn't the carb. But some on this forum don't believe in vapor lock on our engines. But, still, I seemed to experience it.

When I got home, my dipstick was hotter than usual, but I was able to keep holding the handle part of it; and the oil was not smoking, or anything, when I took off the oil cap to check it.

Any suggestions on how to avoid this in the future? Does sanding the flange tube really help?

Tim

[Portlandhipsterwhip]

My brotha, it sounds like vapor lock, definetly. have you tried checking the temp of the fuel pump? feeling it? checking the dipstick temp? It seems our cars just can't handle the heat ( no pun intended ). I'm having a similar problem, where I cruise down the freeway for 15 mins, then i start getting what seems like fuel starvation symptoms, jerking, hesitation, and the gas pedal / throttle body feels rough when i push on the pedal. I'm going to get a 52$ electric fuel pump from orielly to see if it corrects the vapor lock, in addition to enlarging the main jet with a reamer kit, and running the carb a little richer, to decrease engine temps.

[Tim Donahoe]

Well, I started up the bug about an hour ago and it was 95 degrees out. It started and ran fine. I went around the block a few times and no problems.

Tomorrow I'm going down to Wolfgang's and talk to Steve. I'll get some new fuel pump gaskets and try the "sanding-the-stalk" procedure on the flange stem. I'll also check to see if the metal fuel line is actually anywhere near the hot manifold (I don't think so, but I'll look into it).

Tomorrow it will be 111 degrees here in Redding, so I'm taking my daughter's Honda to work--and to Wolfgang's before he closes for the day.

If this keeps up, Port, I may go your route and try for the electric fuel pump. But those scare me a bit, since they surely pump all the time--even after an accident.

Tim

[Portlandhipsterwhip]

As for the electric fuel pump, mount it in the engine bay, but not on the fanhouse or anything, and splice it to the wire that goes to the coil that's the ignition switch, that way it will only pump fuel when the key is turned to the on position. so when you turn your key off, your fuel pump wont be pumping. The fuel pumps only put out around 3lbs, so if you're really worried, put a cheap mechanical regulator inbetween the pump and the carb.

I'm not even gonna worry about it, i'll be putting the electric pump without a regulator to the carb, and just see how it goes.

sometimes i've gotta take a step back, and just realise, it's a friggin car, and it's mechanical, most of the results, even though they are bad ( like vapor lock, etc. etc.) are consistant, so there's gotta be a problem somewhere.

The starting the bug in 95* is normal, it's hot here too in portland. What the problem seems to be, is that when the motor gets hot, since the fuel pump is sitting right on the motor, the fuel pump gets hot too, and it only takes 140* or so to start simmering the fuel.

If I were you, get electronic ignition from www.svda-distributor.com or www.compufire.com. that way you can rule out any electrical problems. This is what I did, and I still have the hesitation on after running for 20 minutes on the freeway, and hard starts like you're having after shutting the car off.

my gas line was sitting RIGHT on top of my exhaust pipe, which reaches almost 600* while warmed up, and it was causing the same problems ( vapor lock ) while driving. so it seems to be a consistant problem in the summer time in hot weather. It's been 90* in portland, and 81 or so at night time, and i'm having the problem at night and in the day.

I dont know how these cars ever ran with a mechanical fuel pump. I guess germany is just lower temps then in the USA. Although ALOT of bugs run in mexico. I dont know.

All I know is that the problem's gotta be fixed, cause every summer there's posts about vapor lock, including my post.

[mrmarcdude]

I wouldn't mount the fuel pump anywhere near the engine compartment. The best way to mount it would be under the tank so it's pushing the fuel to the rear as well as having gravity help feed it fuel. Mounting it to the positive side of the coil is a bad idea as well. Let's say somebody t-bones you while you're going through an intersection, and it knocks you out cold. Sure, the engine may die, but so will you because you aren't awake to flip the key off in the case that there is an engine fire.

If you can, find the root of the problem. Why is your engine running hot? It could be that it needs to be tuned, or you might be missing tin? Have you checked to ensure that the fuel line isn't resting against the heat risers? Maybe it's as simple as installing some decklid standoffs? Installing an electric fuel pump to "fix" the problem is merely just masking over the real cause of your issue.

Sanding the pump base would work IF it's squeezing the pushrod when the case heats up. Some of the aftermarket bases are a little fat where they enter the case, and sanding them is required. The mechanical fuel pump in my car works perfectly even in 110 degree heat. Sure you might have to depress the accelerator slightly after a little heat soak period, but that's pretty much normal considering the temperatures you're operating in.

If you insist on installing an electric pump check into installing a rabbit fuel pump relay, or this - http://www.revolutionelectronics.com/Fuel_Pump.html
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-65 Beetle -1600dp-

[Q-Dog]

The only time I ever had vapor lock in a beetle was on one with an electric fuel pump mounted in the engine compartment. After 30 minutes of running the pump would get hot and the engine would die, but the pump would continue to run and run without pumping fuel. Dumped water on the pump and it started pumping again. I moved the pump out of the engine compartment and the vapor lock issue went away.
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'69 Dune Buggy
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[DeathTrap]

[Jeff_Birt]

A quick web search turned up: http://en.wikipedia.org/wiki/Vapor_lock

The thing to remember is that vapor lock describes a specific condition, that is engine heat causing the fuel to vaporize. Since you fuel pump does not pump vapors well and your carburetor does not handle vapors well problems insure. When the car is running the fuel moving through the system helps keep things cool, when you stop the fuel is stagnate and can vaporize.

I think the 'sanding' being mentioned refers to reducing the diameter of the fuel pump push rod so it does not stick where it passes through the housing. (This problem is not vapor lock.)

[Max Welton]

The stock fuel pump is a positive displacement pump, meaning that it moves fuel by the action of the moving diaphram. The diaphram changes the volume inside the pump, pushing the liquid fuel out. This works because liquid fuel is essentially incompressible.

Fuel in gaseous form simply compresses a little inside the pump when the diaphram moves. The facet style electric pumps are also a positive displacement design and can also vapor lock if allowed to get hot enough.

Electric fuel pumps get around vapor lock not because they are electric but because they can be located somewhere that does not get as hot as the engine, like under the fuel-tank.

Max
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[johnnypan]

Mechanical fuel pump has a check valve in the diaphram that allows the fuel to travel one way while the diaphragm moves...this is how the pump works.In very hot weather the small check valve spring and shaft bind,holding the check valve open,and the pump quits pumping.Carry a spare pump and you can fix the issue...after 6 pumps on my car I went rotary electronic...problem solved for good.

It is not vapor lock...with vapor lock opening the fuel cap and pulling the outlet line off the fuel pump then cranking fixes vapor lock.. try that the next time you think you have vapor lock...if it doesn't fix the issue, its the pump.

[Kiptere]

Vapor lock is real. An electric fuel pump saved me. Mount it up by the gas tank. An electric fuel pump should push fuel not pull. I mounted mine on that little triangle shelf the floor pan makes under the passenger front wheel. Mount the fuel filter infront of the pump. I haven't had any problems since.
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[volksworld]

and if you use a facet mount it on 2 stock injected bug rubber fuel pump mounts so you don't have to listen to it tick

[Tim Donahoe]

DeathTrap. The Wikpedia piece is very informative.

And you sand the "outside" of the lower portion of an aftermarket fuel-pump flange so that it fits nice and easy when installed. some you have to push hard to seat. Unless you take away some of this material, when the engine gets hot, your pump rod can be squeezed and it doesn't move properly (conjecture maybe).

Johnnypan: do you remember what "rotary electronic" unit you hooked up? I assume you installed it under the gas tank--but what do I know? Did it come with good instructions?

I ask because here in Redding, CA, we have many summer days that reach 110 degrees. I had no problem previously (104 F was the highest temperature until yesterday) like the one I had yesterday--but it was really, really hot. Still, I want to be able to drive the car in any temperature--without having to "wash down" my fuel pump when I go to the store.

I may go ahead and install stand-offs, too--although I thought my four sets of lid louvers would do the trick ....

Thanks, everyone,

Tim

[johnnypan]

it was a carter,rated at 3.5 psi..and use a tennis ball,standoffs are for guys with mullets..

electric fuel pumps push better than pull..so put it under the tank..and wire it like this..

http://www.speedyjim.net/schem/pump.gif

[jbuzzvw]

you know it may sound funny but i had this problem years ago on an old duster i owned. thing vapor locked so bad i had to push it off the highway and sit in burger king for an hour. my dad told me an old race car trick he used when he was younger was put wooden close hangars along the fuel line in the engine compartment. they act like a heat sink and wick the heat away from the line. didnt have any more problems the rest of the hot ass summer and it was great conversation starter at the car show haha.

[Tim Donahoe]

jbuzz--that sounds like some good 'ole "snake-oil" b.s. to me--but you may have something there, regardless.

Sometimes the silliest fixes are the ones people think would never work.

It certainly beats hiring some little orphan kid to stand by my motor with a squirt bottle when I go to the store ....

Tim

[Multi69s]

Tim,

Obviously you have a heat related issue. However, vapor lock after only 6 miles of driving is highly suspect. If you look at the history of VWs they have been driven in stock form in just about every weather condition that may be encountered. From Africa to the ice belts. I live in Fresno, so I feel the heat like you do. However, my daily driver is a 2110 with a mechanical fuel pump and I have never had any problem with vapor lock. If you said that you did a 30 minute freeway run and then had problems, I might lean towards vapor lock, but since it was only 6 miles, I would look at the ignition. Both coils and condensers are notorious for breaking down when the temps get too high and I have experienced this problem. The engine will hardly start and when it does, it feels like you only have half of the HP. If you have a spare coil, swap it out, but if you have to spend $$, the first place I would start is the condenser.
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[Tim Donahoe]

So I ran the car yesterday and it ran like always. Today, I checked around the engine bay and discovered that my metal fuel line is actually touching my manifld--although, I do have it wrapped in a protective sheath--like the kind you use to wrap wiring--plastic and ribbed.

I'm missing the plug-wire/fuel hose holder that pushes into the shroud. I ordered one from Wolfsburg West, and I'll re-route this metal feed line like it's supposed to be.

My condenser is not that old and was purchased here in town at Wolfgang's. They have good condensers, coils, plugs, rotors, etc., so I will look into the electrics if, after re-routing the fuel line, I still have a problem.

Thanks, everyone.

Tim

[Q-Dog]

[johnnypan]