Vapor Lock Fuel Line

[Finnd]

Hi All,

Just wondering if anyone has had any experiance with a vapor lock in the fuel?

Our mechanic is thinking the Motorhome (Allegro) may be experincing the fuel pump shutting off when the gas level is lower than 1/3 due to the excessive heat build up in the tank and fuel line.

Has anyone experianced a similar condition?

Thanks

 

[Tom]

A search on "vapor lock" (use the Search button in the toolbar above) will find a number of prior discussions.

 

[max49]

Has anyone experianced a similar condition?

Thanks

Yes, but a new fuel pump seemed to cure it.  I assume you have fuel injection which means your fuel pump is in the gas tank and is cooled by gas.  I only had problems if I had less than half a tank.  Adding cool fuel always cured it temporarily, I guess because it cooled the fuel pump.  I don't understand why but general consensus seems to say you can't get 'vapor lock' with fuel injected engines, altho I still think it is possible. 

 

[Finnd]

Thx Max...is cool fuel a type of fuel?...

although im looking for a permenent fix and yes its fuel injected....

I alittle wary of replaceing the fuel pump as how do i know its not going to happen again?

Thanks

 

[Lou Schneider]

What kind of chassis do you have?  The early to mid 1990 Ford F53s were notorious for fuel pump failures right around 50,000 miles.  As was explained to me, as the pump seals wore out friction between the impeller and the side of the pump increased, raising the intake temperature enough to boil the fuel and create vapor lock at the pump's intake, before it's pressurized.

New pumps use roller bearings instead of wiper seals, which eliminates the problem.

 

[Icemaker]

What kind of chassis do you have?  The early to mid 1990 Ford F53s were notorious for fuel pump failures right around 50,000 miles.  As was explained to me, as the pump seals wore out friction between the impeller and the side of the pump increased, raising the intake temperature enough to boil the fuel and create vapor lock at the pump's intake, before it's pressurized.

New pumps use roller bearings instead of wiper seals, which eliminates the problem.

Thanks Lou, I was mind blocked trying to understand how a pressurized fuel system got "vapor-locked".

 

[Lou Schneider]

So was I, until it was explained to me here.  The failure is gradual, I lived with mine for the better part of a year with gradually worsening symptoms before finally getting a vapor lock at a critical point that forced me to get it diagnosed.

 

[zukIzzy]

So was I, until it was explained to me here.  The failure is gradual, I lived with mine for the better part of a year with gradually worsening symptoms before finally getting a vapor lock at a critical point that forced me to get it diagnosed.

There are 2 types of high pressure fuel pump one is a roller vane and the other is a gear rottor. Both of them use a volume differential principal. Both use very high tolerance parts to seal while operating. As these parts wear the tolerances get looser and this causes some "slip" if you will eventually this "slip" causes the fuel to reach the vapor separation temp/velocity "cavitation". (ever ridden in a boat and seen the white trail coming right off the prop? this is the same type of "slip" and resulting cavitation). Cavitation will cause stainless steel parts to rub against each other causing more heat until right at the pump impeller it is hot enough to boil a small pocket of vapor and the pump stops pumping. You pull to the side of the road and grab the cell phone make a call check what you can hold your head in your hands and out of pure frustration you try it again and varroooom you are off again for a few more minutes until it all happens again.

More fuel provides a bit of head pressure to help the pump intake easier and some cooling for the pump to prolong the chain of events.

That is Vapor lock in a pressure system. I do fuel systems for desert race cars everyday. Depending on the additives in the fuel, you can get vapor separation at about 130* at the intake and it takes about 300* in the pressure side at 60psi. you will have bigger problems if the pressure side reaches *300. like getting out of the thing.

thanks
Wayne

 

[Icemaker]

Thanks Wayne, I understand the concept of "starving" a pump, restricting flow, either by line lose or a valve throttling flow or even a "kink", or creating low pressure areas by over speed. It is just that on a pump w/o a restriction, as I imagine a pump immersed in a fluid, I missed the worn and increased tolerances causing the slippage..I gather they work mostly on centrifugal pumping as opposed to positive displacement pumps.
Since I have similar issues w/fuel oil pumps I should have transferred that knowledge to the fuel pump in a tank..as my Grandchildren often say.."My Bad"..
Had a fuel oil tank that had a small kids toy in it that had settled to the bottom, more nuisance calls than can be believed, that didn't get found till the tank was emptied and there it was. But I digress.
Again Thanks for the refresher and I'll use variations of this in my pump classes..

 

[zukIzzy]

No positive displacement very similar to an oil pump. But think of the lower pressure at the intake like all pumps have and think of the adatives in gasoline. Alcohol boils at 174* at sea level now go up to 4000' and apply a bit of suction no matter how the pump is mounted there will be a stilght drop in pressure at the tank. Now make that be middle of summer pulling the boat to the river and the pump uses a few more of the finite revolutions it was built for. Oil pumps can do the same but due to the lower volatility and inherent lubrication of oil the conditions need to be more extreme to start the chain.

What pump class? I'm a hard knocks kind of guy with barley a high school educumation. would be interested to pick up some knowledge if you have any to share.

 

[zukIzzy]

OH and acetone boils around 130* sea level and is use often as an octane booster.

last edit ethanol is 172* not 174* sorry i missremembered ;D

 

[Icemaker]

I'm a pipefitter/HVAC&R

modified as the posting went weird..
I'm a instructor for a local plumbing/pipefitting union. As one of the instructor i teach a variety of piping courses related to heating, steam & water boilers, some solar and "green awareness" classes and other topics related to construction & mechanical work.

 

[rls7201]

Lots of good theory but brush failure is also a problem. That's what happened to my Ford F53 fuel pump.

Richard

 

[donandmax]

What kind of a fuel pump do I ask for and if I get a replacement how do I know its not the old failure prone kind ?

 

[RLSharp]

What kind of a fuel pump do I ask for and if I get a replacement how do I know its not the old failure prone kind ?

I would be extremely surprised if there are any of the original fuel pumps still for sale, especially from a Ford dealer. The original fuel pump went through two revisions before Ford got the problem solved. That was in the mid- to late-90s and the old stock would be gone by now. This assumes that you purchase the pump through a Ford dealer. Buying one from the Internet and all bets would be off.

BTW, if I remember right, there was thread on the forum that gave an actual Ford part number for the new pump.

Edit: The part number and TSB can be found at: http://www.rvforum.net/SMF_forum/index.php?topic=44035.msg406013#msg406013

R

 

[Tom]

Adding to Richard's comment, use the Search button in the toolbar above (not the one at the top of the page) and search on "fuel pump" (include the quotes).

 

[Wanderingcanuk]

I was having the same problem this last summer (prob due to the extreme heat). I picked up some heavy gage black rubber tubing (automotive tubing), sliced it down one side and slipped it over the gas line from the carb to the back of the engine (zip tied in place). Drove from Winnipeg to Myrtle Beach and back in the July 2012 heat and no difficulties at all. Used to do this on the farm tractors to avoid the vapour lock.

 

[zukIzzy]

I was having the same problem this last summer (prob due to the extreme heat). I picked up some heavy gage black rubber tubing (automotive tubing), sliced it down one side and slipped it over the gas line from the carb to the back of the engine (zip tied in place). Drove from Winnipeg to Myrtle Beach and back in the July 2012 heat and no difficulties at all. Used to do this on the farm tractors to avoid the vapour lock.

Carbs and FI do not suffer the same vapor lock. But yes that is a clasic fix for carb vapor lock.

wayne