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Vapor Lock/Fuel Boil
#1493631
08/31/13 07:57 PM
08/31/13 07:57 PM
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Joined: Jul 2012
Posts: 102
pensacola, fl
53fopar
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Posts: 102
pensacola, fl
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I've got a vapor lock issue that I can't seem to fix. The engine is a 1977 360, stock heads, Summit intake, Edelbrock 1405, and Headman headers. Running Vintage Air. Three core AL radiator with full shroud and electric fan and 160* thermostat. Engine runs cool, normal 170. Gets to 180-185 if sitting in traffic with AC on. It does get very hot under the hood with the puller electric fan. This all in a 1953 Ford F100 panel truck For the past few weeks when it's hot (90-95*) the engine will vapor lock if I drive it for an extended period. When engine is cool it starts and runs fine. Even hot re-starts are no problem. However, if I run it for a long run with the AC and the engine temp gets up to 180* it will die. When I look under the hood the small in-line Mr. Gasket fuel filter up by the carb is empty. No amount of cranking will re-start. Tried to vent the gas cap and removing fuel line, no help. The only way to get the engine to re-start is to allow it to cool some and then dump some gas in the carb to prime it. If I just let it sit for 2 to 3 hours the fuel filter refills and the engine will start with one or two pumps. I can repeat the problem by letting it idle with the AC running for about an hour and then it will die and fuel filter will be empty. I have tried the following: new electric fuel pump (Holley 12-125) mounted next to fuel tank. One inch plastic spacer under the carb. Re-ran all the fuel line away from headers. Came along the floor and up the fire wall with all new 3/8 fuel line. Tried to keep fuel line out of engine bay as much as possible. Line comes from behind distributer to back of carb. The only original fuel line is about 18" coming out of the tank. So, where do I go from here? The only things I can think of don't seem likely to help. Rebuild carb? Insulate the fuel line? Is there a way to ventilate the engine bay? 
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Re: Vapor Lock/Fuel Boil
[Re: 53fopar]
#1493633
08/31/13 08:16 PM
08/31/13 08:16 PM
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Joined: Jan 2007
Posts: 7,664
IN
ahy
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Boy... it sounds like you have done everything. Fuel lines, carb spacer, electric pump. If the electric pump won't push fuel up there I don't know what will.
A couple of suggestions. Have you bypassed the OE fuel pump completely? Also how about the tank and pickup? If there is debris in the tank that is clogging the pickup screen that could shut her down when things get hot. Also, most important with an electric pump is low restriction on the suction side. Clean tank, clean screen, preferably 3/8"+ suction line and fuel pump as low as possible help.
Last edited by ahy; 08/31/13 08:30 PM.
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Re: Vapor Lock/Fuel Boil
[Re: 53fopar]
#1493637
08/31/13 11:36 PM
08/31/13 11:36 PM
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Joined: Feb 2005
Posts: 28,312
Cincinnati, Ohio
Challenger 1
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Cincinnati, Ohio
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Quote:
The OE pump is gone and hole blocked. There is some small trash in the filter before the fuel pump. I never had the tank out. It runs fine if it's not hot so I am thinking it's not a trash issue. Is there some way the heat would increase the trash problem?
There's about 18" of steel 1/4" fuel line coming from the tank pickup then changes over to 3/8" hose. When it vapor locks the fuel filter between the tank and the electric pump stays full so I don't think it's a suction issue. Really seems like vapor lock or fuel boil since it's directly related to hot operation.
First I would suggest to get a better fan that moves more air.
Second you can't have 1/4"ID on the suction side and expect the pump not to struggle when it get's hot. Also I suspect the filter you have in front of the pump is a 10 micron filter which is too fine for hot weather/hi volume use.
I suggest to only use a new strainer before the fuel pump, not a filter.
Gas is really hard to suck, especially during hot weather. You can restrict the flow with too small of line size and filters before the pump.
Normally you would return the fuel through the sending unit, maybe you should put one back in your tank?
Good luck.
And this should be in the general section since it's not a Mopar.
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Re: Vapor Lock/Fuel Boil
[Re: 53fopar]
#1493639
09/01/13 12:49 PM
09/01/13 12:49 PM
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Joined: Feb 2005
Posts: 28,312
Cincinnati, Ohio
Challenger 1
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Don't remove the filter after the pump, it needs to be there and is not the cause of your problem.
The filter before your pump part of the problem, I can promise you that much.
I don't feel that under hood temps is causing your problem, it's fuel supply issues, I'm sure.
Can you remove your hood for a day and go drive the truck and see if I'm right?
A good strong pump is because it has a large unrestricted supply of gas to it. That's why pumps work good.
A good working pump will easily push fuel into a hot engine compartment.
The hotter it get's the harder it is to suck gas, it vaporizes real easy under vacuum conditions and no fuel pumps can suck or pump vapor. It might work alright during cool days but when it get's hot out, it the gas turns to vapor real easy on the suction side of your pump.
If that's the case then the fuel pump will have a shorter life too.
Last edited by Challenger 1; 09/01/13 01:04 PM.
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Re: Vapor Lock/Fuel Boil
[Re: TJP]
#1493641
09/01/13 03:13 PM
09/01/13 03:13 PM
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Joined: Jul 2012
Posts: 102
pensacola, fl
53fopar
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Joined: Jul 2012
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pensacola, fl
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No, not ethanol problem. I run ethanol free marine fuel. I went out and removed the Mr Gasket in-line filter next to the carb and put plastic wire loom over the fuel line in the engine bay. No other changes. Ran the truck with cardboard in front of radiator to get engine temp up to 195-200. Then went for a ride. No vapor lock. As I drove the temp came back down to 180. Repeated with the cardboard and still no issues. Did several hot re-starts without problem. I am going to drive the truck some more this afternoon and see what happens. Could the glass/metal in-line filter be acting like a heat sink and suck up the heat from the engine bay? 
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Re: Vapor Lock/Fuel Boil
[Re: Mr.Yuck]
#1493643
09/01/13 04:19 PM
09/01/13 04:19 PM
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Joined: Jul 2012
Posts: 102
pensacola, fl
53fopar
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Yeah, it might be 5/16". The only section of it is on top of the tank coming from the pick-up. It's up tight to the floor board and I can barely see it, let alone remove it.
Last edited by 53fopar; 09/01/13 04:29 PM.
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Re: Vapor Lock/Fuel Boil
[Re: 53fopar]
#1493645
09/01/13 04:35 PM
09/01/13 04:35 PM
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Joined: Feb 2005
Posts: 28,312
Cincinnati, Ohio
Challenger 1
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Cincinnati, Ohio
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Quote:
Well, back to the drawing board. Took it out this afternoon and drove it hard. After about an hour and half it died. Fuel pressure gauge reads 0 with the pump running. No fuel in the carb. Fuel filter between tank and fuel pump is full. Temp when it died 185*.
Don't be confused, by the time you look at the filter that shouldn't be there is has turned back to liquid and you can't see vapor lock at the inlet of the pump. That's where it occurs, not up by the engine with a electric pump.
Just trying to help you, been there and have done it more than once.
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Re: Vapor Lock/Fuel Boil
[Re: moparcanuk]
#1493649
09/01/13 06:32 PM
09/01/13 06:32 PM
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Joined: Sep 2007
Posts: 14,889
up yours
Supercuda
About to go away
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About to go away
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Posts: 14,889
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It may be possible your fuel line before the pump is leaking air into the fuel. As it warms up, the crack opens up, heck it could very well be your pump overheating and flaking out.
They say there are no such thing as a stupid question.
They say there is always the exception that proves the rule.
Don't be the exception.
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Re: Vapor Lock/Fuel Boil
[Re: ahy]
#1493652
09/02/13 01:48 AM
09/02/13 01:48 AM
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Joined: Feb 2005
Posts: 28,312
Cincinnati, Ohio
Challenger 1
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Cincinnati, Ohio
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Quote:
If you have a clean sound "sock" on the fuel pickup that should protect the pump. It serves the same purpose as the 100 micron filter before the pump. Personally I'd pull the pickup next and have a look see. If the sock is intact and is clean or can be cleaned, simply remove the filter before the pump for a test.
Summit does have the 100 micron filters if you really want or need one. A local speed shop, if there is one near you, should have them also.
Exactly...
But this is a ford panel truck... I bet your sock/strainer in the tank is old/dirty and could be causing the restriction.
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Re: Vapor Lock/Fuel Boil
[Re: Challenger 1]
#1493653
09/02/13 12:06 PM
09/02/13 12:06 PM
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Joined: Jul 2012
Posts: 102
pensacola, fl
53fopar
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Posts: 102
pensacola, fl
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I am going to try the 100 micron filter before the pump to see if it was a flow restriction there.
The only way to check the sock/pickup is to drop the tank. But, I still don't understand how that could be the problem. The engine runs fine in cool weather (anything under about 80*). This ONLY happens when it's hot outside. I still think it's a vapor lock/fuel boil issue.
Last edited by 53fopar; 09/02/13 12:15 PM.
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Re: Vapor Lock/Fuel Boil
[Re: 53fopar]
#1493656
09/03/13 11:57 PM
09/03/13 11:57 PM
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Joined: Jan 2007
Posts: 7,664
IN
ahy
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master
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Posts: 7,664
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Re: Vapor Lock/Fuel Boil
[Re: 53fopar]
#1493657
09/04/13 10:31 AM
09/04/13 10:31 AM
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Joined: Jan 2003
Posts: 75,047
U.S.S.A.
JohnRR
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Quote:
Before I go through dropping the tank, I think I'll try a test. I am going to pull the fuel line off the tank and put it in a gas can. I'll also remove the filter ahead of the pump. If it still shuts down running from a gas can, I'll have to re-think. If it runs, I'll drop the tank, clean, seal and new sock. Sound like a reasonable plan?
This is a good test , use a boat fuel tank for max safety and lose the pre pump filter.
One thing you did that made zero sense was removing the filter AFTER the pump , you should have removed the filter before the pump it's too fine for the pump to suck thru.
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Re: Vapor Lock/Fuel Boil
[Re: JohnRR]
#1493659
09/04/13 10:12 PM
09/04/13 10:12 PM
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Joined: Jul 2012
Posts: 102
pensacola, fl
53fopar
OP
member
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OP
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Joined: Jul 2012
Posts: 102
pensacola, fl
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Quote:
This is a good test , use a boat fuel tank for max safety and lose the pre pump filter.
One thing you did that made zero sense was removing the filter AFTER the pump , you should have removed the filter before the pump it's too fine for the pump to suck thru.
I was thinking the in-line Mr Gasket was drawing heat since it was up front by the alt. I've ordered the Holley 100 micron pre pump and 40 micron post pump filters and will mount them by the pump.
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Re: Vapor Lock/Fuel Boil
[Re: TJP]
#1493660
09/04/13 10:16 PM
09/04/13 10:16 PM
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Joined: Jul 2012
Posts: 102
pensacola, fl
53fopar
OP
member
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OP
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Joined: Jul 2012
Posts: 102
pensacola, fl
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Quote:
I wouldn't seal the tank. I have seen all too many sealed tanks fail and create a mess. If your tank is contaminated just put a new one in they are relatively inexpensive 
New tank for this truck is $500 plus oversized shipping. I am going to try the KBS clean/seal system. I seen several good reviews. Anyone here used it?
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