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10/28/2018 9:44 PM  #1


How hot does fuel need to be to vapor lock? Installing new fuel line.

So today I made up some clamps to secure the new line I made up (the clamps are 1"x1").  Now I have 3/8" line from the pump to the carburetor instead of 5/16".  The clamps are aluminum and are bolted to the drivers side head.  Is the heat transfer a worry?  Anyone know how hot gasoline needs to get to cause vaperlock?  I'm thinking of cutting out some small squares of 1/8" thick fiberglass insulating panel and putting them behind the clamp… But that may be a complete waste of time if not needed.

Thanks,
Peter





 

10/29/2018 7:31 AM  #2


Re: How hot does fuel need to be to vapor lock? Installing new fuel line.

Pure gasoline vaporizes at 140 degrees, BUT ethanol is more like 174 degrees, so the gas we all use being 10% ethanol is going to in theory have a slightly higher point of vaporization, assuming a homogeneous mixture.

My concern would be exhaust heat.  My fuel line from the pump (engine mounted) to the carb runs right past the #2 header tube, but I've never had an issue with vapor lock, even when it was past 95 degrees outside.  The headers are ceramic coated, which means they radiate less heat that uncoated headers, and my fuel line is aluminum, which rejects heat much better than steel and steel alloys.  In  general though. try to keep it away from the exhaust and I think you'll be fine.  I would not for example run the fuel line along the vale cover above the header, as that exposes a considerable surface area to heat. 

As far as heat transferring through the clamps to the fuel line, I don't think I'd worry.  The clamps are aluminum, so they will tend to reject heat. 

 

10/29/2018 7:41 AM  #3


Re: How hot does fuel need to be to vapor lock? Installing new fuel line.

LOL, aluminum rejects heat! - - - stick your thumb on a frying pan thats on a burner and make that statement again.
 Anything that is aluminum, bolted to an engine will very shortly become the same temperature as the area to which it is attached.


Good work ain't cheap, Cheap work ain't good!   Simple Man
 

10/29/2018 3:23 PM  #4


Re: How hot does fuel need to be to vapor lock? Installing new fuel line.

Take a cast iron skillet and an aluminum frying pan and put them on the same heat.  Once at temperature remove them from the heat and check the temperature after 5 minutes, then 10.  You'll be able to handle the aluminum pan long before the cast iron skillet.

Heat rejection isn't about a metal's ability to be brought up to or hold temperature in the constant presence of heat.  If I put anything in an oven its going to become the temperature of the oven, and likewise, if I bolt anything to an engine its going to become the temperature of the engine.  But, when the heat isn't constant, or when there's air circulation, aluminum is going to reject heat better than any other common metal.  Note this isn't a questions of insulation, which would be preventing heat transfer.  I think this is where the confusion might lie.  

If you want insulation from heat you need something to reflect heat like foil faced wrap, or some form of insulation to prevent heat transfer like a phenolic.

 

10/29/2018 4:28 PM  #5


Re: How hot does fuel need to be to vapor lock? Installing new fuel line.

Like I said " Anything that is aluminum, bolted to an engine will very shortly become the same temperature as the area to which it is attached"
It's called heat soak, so if the fuel is susceptable to vaporisation  the heat from the bracket will be transferred to the fuel line and possibly contribute to vapor lock.


Good work ain't cheap, Cheap work ain't good!   Simple Man
 

10/29/2018 5:59 PM  #6


Re: How hot does fuel need to be to vapor lock? Installing new fuel line.

If not to late...why not slip a piece of shrink tube over fuel line (inside clamp) to act as insulation/heat break or just a piece of rubber?
6s6


Get busy Liv'in or get busy Die'n....Host of the 2020 Bash at the Beach/The only Bash that got cancelled  )8
 

10/29/2018 7:20 PM  #7


Re: How hot does fuel need to be to vapor lock? Installing new fuel line.

I'll craft up some sort of insulator next week… First priority is to get this thing running and moving again.  Going to try to get it mobile tomorrow, but it will take complete hackery with some very temporary wiring.

 

     Thread Starter
 

10/30/2018 9:38 AM  #8


Re: How hot does fuel need to be to vapor lock? Installing new fuel line.

Aluminum is also the best metal for combating heat soak, which is why its used in heat sinks in electronics.  Often heat sinks have a means of air circulation used in conjunction (CPU fan, etc.), but not always.  When in motion I think you've got enough air circulation.  The potential problem is once you stop and the car sits, but at that point what the fuel line clamps are made from doesn't matter, because the engine bay has become an oven.  Its radiating and holding heat as much as its transmitting heat at that point.  So if the fuel line's going to get hot enough to vaporize the fuel its going to get hot enough from the radiant heat.  The clams could be phenolic at that point and the fuel's still going to vaporize.  In the end the way the line is routed is going to make a much larger difference than what the clamps are made from. 

In general, thinking about how every OEM setup was done that I can think of, fuel lines run through the engine bay for the shortest amount of distance possible.  As far as heat transmissions goes though, at some point the fuel line is connected to the engine.  The engine is hot, and is going to conduct heat into the fuel line.  Its also by no means uncommon for fuel lines to be clamped to the engine in one of more spots to aid routing.  This is typically done with steel or plastic clamps.  Depending on the plastic, in order of best possible choices I would rank them: plastic, aluminum, and steel in terms of preventing any heat related issues.  But plastic has its own problems, mostly that it gets brittle and fails. 

 

10/30/2018 8:04 PM  #9


Re: How hot does fuel need to be to vapor lock? Installing new fuel line.

I would not use those blocks to mount the fuel line. They will heat soak that portion of the tubing, plus they just are not necessary.

I just made a new steel line for my truck’s 5.0 and it is very rigid with only one support behind the edelbrock carb. For front entry carbs, no mounts are needed to have a very solid fuel line.

For the one mont I did use, I salvaged a spring steel clamp from a 5.0 EFI system and welded it to my throttle return spring bracket. It has very little cross-sectional area to transfer heat.


Money you enjoy wasting is NOT wasted money... unless your wife finds out.
 

10/31/2018 8:54 AM  #10


Re: How hot does fuel need to be to vapor lock? Installing new fuel line.

With a timing cover mounted fuel pump and front fed carb I've never had need to add clamps to the fuel line.  My setup has no rubber line in it.  Hard line from the carb to the filter, hard line from the filter to the pump.  Adapters used as needed.  Works great, even with aluminum line that is less rigid than steel. 

Last edited by TKOPerformance (10/31/2018 11:51 AM)

 

10/31/2018 11:47 AM  #11


Re: How hot does fuel need to be to vapor lock? Installing new fuel line.

I used AN stainless braid hose and fittings.
 By the way, don't you think the fuel pump is going get just as hot as a fuel line bolted the engine?

Last edited by Rudi (10/31/2018 11:51 AM)


Good work ain't cheap, Cheap work ain't good!   Simple Man
 

10/31/2018 12:02 PM  #12


Re: How hot does fuel need to be to vapor lock? Installing new fuel line.

 I think that today's fuels are different than back in the day when my DD was  a  62 Mercury Meteor with a 221 Windsor, that's the last time I  had vapor lock.
Please raise your hands if you have  had vapor lock with modern gas.


Good work ain't cheap, Cheap work ain't good!   Simple Man
 

10/31/2018 8:49 PM  #13


Re: How hot does fuel need to be to vapor lock? Installing new fuel line.

Rudi wrote:

 I think that today's fuels are different than back in the day when my DD was  a  62 Mercury Meteor with a 221 Windsor, that's the last time I  had vapor lock.
Please raise your hands if you have  had vapor lock with modern gas.

Pick me Pick me, Mid nineties we were headed to Mount Rushmore in a Dogde caravan, vapor locked north of Alliance Ne. 3 hot kids and a hot wife. No fun. 100 degrees outside. 
Same trip had to run the heater to get back home, went through Ogallala, bank thermometer said 103.

(Hot wife, not the good kind of hot)
 


67 Coupe, 5.0 EEC IV Fuel injected. T5, 3:70 rear
 

10/31/2018 9:02 PM  #14


Re: How hot does fuel need to be to vapor lock? Installing new fuel line.

The only thing I have experienced vaporlock in was my buddies Grumman van.  The fuel line was right next to the exhaust along the frame rail and would get cooked going over a mountain grade. Fixed it with a goofy insulation sock for the hard line.

For now I am going to leave the line the way it is, but put the clamps on a diet in the mill to make them a little less chunky, and set them off on some high temp rated fiberglass insulating board.  Future land might have a 100% hard line solution...

     Thread Starter
 

11/01/2018 7:54 AM  #15


Re: How hot does fuel need to be to vapor lock? Installing new fuel line.

The ethanol in the fuel raises the temperature of vaporization somewhat.

Vapor lock can occur on almost any vehicle, especially if something isn't working right.  I troubleshot a condition that turned out to be vapor lock on my '02 WRX.  Car ran fine, but once it heated up if you shut it off for more than a few minutes you could not restart it for about 20-30 minutes.  Extensive testing revealed that after shutdown the rail pressure continued to climb, until it basically pegged my gauge (200psi).  If I vented the pressure I could restart the car.  I then took a can of Dust Off and blasted the fuel pressure regulator with it to cool it down.  I watched the pressure drop as the FPR started bypassing again, and voila the car started again.  A new FPR and problem solved.  EFI with vapor lock, which a lot of guys will tell you doesn't happen.  I've got to wonder how long it would have taken the clowns at the dealership to figure that one out. 

 

Board footera


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