Vapor lock - The 1947 - Present Chevrolet & GMC Truck Message Board Network

s95930 · 11-27-2003, 02:05 PM

I have a 70 3/4 ton GMC. I am having a problem with Vapor lock. I have replaced the filter and fuel pump. I finally figured out that the fuel line from the tank to the pump is getting hot. The exhust pipe runs right between the starter and the frame. And it all gets very hot there. I figured out this was the problem by running it till it was hot and was starting to vapor lock then spraying water on the frame. It started pumping fuel great again after it was cooled.

I have I believe a stock 350 in it. No headers etc.

I am considering rerouting the fuel line. But, I have never seen anyone else discuss this problem.

Have you had the same problem?

What did you do about it?

If you have not had the problem am I missing something?

It seems to me that if everyones truck is set up like mine they should all have the same problem.

Cat Fuzz · 11-27-2003, 02:15 PM

You could reroute the fuel line. Or you could construct some kind of heat shield using pipe clamps and sheet metal.

Also, maybe the fuel line got mesed with and is just a bit too close to the pipe and bending it away just a few inches might do the trick.

I'd have to go look at mine to remember how its routed.

s95930 · 11-27-2003, 02:19 PM

The fuel line runs inside the frame rail. It is fastened to it with clips. I am also thinking of usins a heat shield.

**old Rusty C10** · 11-27-2003, 03:48 PM

your setup creates too much heat fabricate some kind of heat shield and make sure the line is kept as far away fromt he headers as possible

s95930 · 11-28-2003, 08:29 PM

ttt

*67Fleetsidedream* · 11-28-2003, 08:44 PM

Get some aluminum foil and wrap it around the fuel line. Don't wrap it around tight. This should dissapate heat well enough to keep it from vapor locking.

Longhorn Man · 11-28-2003, 11:33 PM

By chance, do you have a fuel filter between the pump and the tank?
This can make vapor lock issues worse, and the more crap in the filter the worse the vapor lock can get.

Ackattack · 11-29-2003, 03:58 PM

Many of us have headers along with the same fuel line setup without issues. I'm going with filter is in the wrong place or clogged.

s95930 · 11-29-2003, 04:56 PM

That is what has me stumped. I figure that everyone should be having thhe same problem. I don't have headers and the only fuel filter is a see through one just before the carb. And I have replaced that filter a couple of times.

Longhorn Man · 11-30-2003, 03:27 AM

A common place for a filter to be installed (I thought they were stock there but I was mistaken) is directly under the cab where the fuel line comes through the floor. I would double check that location for a filter.
If there is a filter between the pump and the tank, then as that filter gets clogged up and imposes a restriction, the fuel pressure drops in that section of line. The drop in pressure will lower the boiling point. (anyone remember the old pressure cookers that worked off this principle...actually the oposite principle)

Another thing to look at is heat can be transfered pretty easily too. If you have a header pipe that is touching the frame, and the fule line is close by, the heat could be passed off to the fuel.

It is odd that you are having this problem at this time of year. It is commonplace in the heat of the summer...but pretty much unheard of in november.

11-27-2003, 02:05 PM	#1
s95930 A-Adam A-Adam Join Date: Apr 2003 Location: Sarpy Co. Ne. South of Omaha Posts: 263	Vapor lock I have a 70 3/4 ton GMC. I am having a problem with Vapor lock. I have replaced the filter and fuel pump. I finally figured out that the fuel line from the tank to the pump is getting hot. The exhust pipe runs right between the starter and the frame. And it all gets very hot there. I figured out this was the problem by running it till it was hot and was starting to vapor lock then spraying water on the frame. It started pumping fuel great again after it was cooled. I have I believe a stock 350 in it. No headers etc. I am considering rerouting the fuel line. But, I have never seen anyone else discuss this problem. Have you had the same problem? What did you do about it? If you have not had the problem am I missing something? It seems to me that if everyones truck is set up like mine they should all have the same problem. __________________ 70 3/4 ton GMC Camper Special

11-27-2003, 02:19 PM	#3
s95930 A-Adam A-Adam Join Date: Apr 2003 Location: Sarpy Co. Ne. South of Omaha Posts: 263	The fuel line runs inside the frame rail. It is fastened to it with clips. I am also thinking of usins a heat shield. __________________ 70 3/4 ton GMC Camper Special

11-27-2003, 03:48 PM	#4
old Rusty C10 Robert Olson Transport Join Date: Oct 2002 Location: recent transplant to NC USA Posts: 20,277	your setup creates too much heat fabricate some kind of heat shield and make sure the line is kept as far away fromt he headers as possible __________________ Bob 1951 International running on a squarebody chassis "If a man's worth is judged by the people he associates himself with, then i am the richest man in the world knowing some of the fine people of this board" http://67-72chevytrucks.com/vboard/a...t.php?f=25&a=9 (you can review the site rules here!) PM Me for your vehicle/parts hauling needs in the North East US or see my Facebook page Robert Olson Transport Live each day to the fullest.. you never know when fate is going to pull the rug out from under you... I hate cancer!!

11-28-2003, 08:29 PM	#5
s95930 A-Adam A-Adam Join Date: Apr 2003 Location: Sarpy Co. Ne. South of Omaha Posts: 263	ttt __________________ 70 3/4 ton GMC Camper Special

11-29-2003, 03:58 PM	#8
Ackattack Senior Member Join Date: Aug 2002 Location: Valley Center KS Posts: 3,525	Many of us have headers along with the same fuel line setup without issues. I'm going with filter is in the wrong place or clogged. __________________ Project Bruiser: 68 Pro-Touring C-10 5.3L / 4L60E Project Ironhide: 97 GMC Crew Cab 4x4 Cummins SOLD: '69 GMC 1/2T SWB TBI'd: Project No Buck Assembly Manual Index Sign up Thread!!! Factory Service Manual Index

11-27-2003, 02:15 PM	#2
Cat Fuzz My son, my joy. Join Date: Sep 2003 Location: Spokane WA Posts: 463	You could reroute the fuel line. Or you could construct some kind of heat shield using pipe clamps and sheet metal. Also, maybe the fuel line got mesed with and is just a bit too close to the pipe and bending it away just a few inches might do the trick. I'd have to go look at mine to remember how its routed.

11-28-2003, 08:44 PM	#6
67Fleetsidedream Wiseass secured himself a BAN Join Date: Nov 2000 Location: MOON!!! Posts: 2,282	Get some aluminum foil and wrap it around the fuel line. Don't wrap it around tight. This should dissapate heat well enough to keep it from vapor locking.

11-28-2003, 11:33 PM	#7
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,693	By chance, do you have a fuel filter between the pump and the tank? This can make vapor lock issues worse, and the more crap in the filter the worse the vapor lock can get.

11-29-2003, 04:56 PM	#9
s95930 A-Adam A-Adam Join Date: Apr 2003 Location: Sarpy Co. Ne. South of Omaha Posts: 263	That is what has me stumped. I figure that everyone should be having thhe same problem. I don't have headers and the only fuel filter is a see through one just before the carb. And I have replaced that filter a couple of times. __________________ 70 3/4 ton GMC Camper Special

11-30-2003, 03:27 AM	#10
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,693	A common place for a filter to be installed (I thought they were stock there but I was mistaken) is directly under the cab where the fuel line comes through the floor. I would double check that location for a filter. If there is a filter between the pump and the tank, then as that filter gets clogged up and imposes a restriction, the fuel pressure drops in that section of line. The drop in pressure will lower the boiling point. (anyone remember the old pressure cookers that worked off this principle...actually the oposite principle) Another thing to look at is heat can be transfered pretty easily too. If you have a header pipe that is touching the frame, and the fule line is close by, the heat could be passed off to the fuel. It is odd that you are having this problem at this time of year. It is commonplace in the heat of the summer...but pretty much unheard of in november.



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