66 Galaxie Gas Cap causing excess tank pressure - Ford Muscle Forums : Ford Muscle Cars Tech Forum
 3Likes
Reply
 
LinkBack Thread Tools
post #1 of 16 (permalink) Old 06-27-2019, 11:55 AM Thread Starter
Registered User
 
Join Date: Nov 2018
Location: Illinois
Posts: 80
66 Galaxie Gas Cap causing excess tank pressure

I seen this discussed before but I've never seen a proper answer to this. My 66 Gal (428 engine) has a new gas tank with about 4 gallons of fuel in it. I just purchased a new NAPA Balkamp (Motorad) gas cap. The product description says this:

OE-style gas caps meet or exceed all original equipment performance and safety standards. Caps are made of sturdy and long-life materials, are the only aftermarket caps to include all safety features and valving of the original equipment caps. Vented anti-surge, with shallow cam

The car is currently not running yet but I go out to work on it every day in the garage. I have to unscrew the gas cap daily or I believe the fuel tank might explode from all the pressure built up inside the tank. The past few days I've just laid the cap on the fuel filler tube and don't tighten it so the pressure will release on it's own.

I'm about ready to take a drill to the cap and put a small hole in it cause this cap isn't vented for outward pressure at all. So how is everyone else solving this issue? Thanks for any advise that can be offered.
7 Litre is offline  
Sponsored Links
Advertisement
 
post #2 of 16 (permalink) Old 06-27-2019, 12:48 PM
Registered User
 
Join Date: Jul 2009
Location: Houston
Posts: 418
Garage
Re: 66 Galaxie Gas Cap causing excess tank pressure

Quote:
Originally Posted by 7 Litre View Post
I seen this discussed before but I've never seen a proper answer to this. My 66 Gal (428 engine) has a new gas tank with about 4 gallons of fuel in it. I just purchased a new NAPA Balkamp (Motorad) gas cap. The product description says this:

OE-style gas caps meet or exceed all original equipment performance and safety standards. Caps are made of sturdy and long-life materials, are the only aftermarket caps to include all safety features and valving of the original equipment caps. Vented anti-surge, with shallow cam

The car is currently not running yet but I go out to work on it every day in the garage. I have to unscrew the gas cap daily or I believe the fuel tank might explode from all the pressure built up inside the tank. The past few days I've just laid the cap on the fuel filler tube and don't tighten it so the pressure will release on it's own.

I'm about ready to take a drill to the cap and put a small hole in it cause this cap isn't vented for outward pressure at all. So how is everyone else solving this issue? Thanks for any advise that can be offered.
How are you determining the pressure is not being released? Just by hearing the pressure release when opening?

Sounds like you may just have a faulty cap. If it's listed as "vented" and it's not releasing pressure, take it back and try another.

'66 Galaxie 2 Dr. Fastback 352 C6

99% of what you worry about won't even happen. Get that car done!
mvannote is offline  
post #3 of 16 (permalink) Old 06-27-2019, 02:18 PM Thread Starter
Registered User
 
Join Date: Nov 2018
Location: Illinois
Posts: 80
Re: 66 Galaxie Gas Cap causing excess tank pressure

If I didn't hold the cap as I unscrewed it, the cap would probably fly across the garage.
7 Litre is offline  
 
post #4 of 16 (permalink) Old 06-27-2019, 07:41 PM
Registered User
 
Join Date: Mar 2014
Location: Indianapolis, IN
Posts: 231
Re: 66 Galaxie Gas Cap causing excess tank pressure

I wonder why the tank has pressure in the first place? I thought the vent was to allow air IN, to keep the tank from being crumpled as the gas is pumped out.


Pat

1964 Galaxie 500 2 dr Fastback, 390, 4 speed, Indianapolis Indiana
1964Fastback is offline  
post #5 of 16 (permalink) Old 06-27-2019, 07:51 PM Thread Starter
Registered User
 
Join Date: Nov 2018
Location: Illinois
Posts: 80
Re: 66 Galaxie Gas Cap causing excess tank pressure

I also thought that Pat. Seems like with that much pressure building up the carb would be flooded. Just rebuilt my carb so I hope the floats are working!
7 Litre is offline  
post #6 of 16 (permalink) Old 06-27-2019, 09:22 PM
Registered User
 
Join Date: Mar 2019
Posts: 33
Re: 66 Galaxie Gas Cap causing excess tank pressure

I've been meaning to ask the same or similar question myself. I have a 68 Galaxie I recently purchased. Whenever I go to get gas there's a huge pressure release when I open the cap. It doesn't seem right to me either.
TonyC2639 is offline  
post #7 of 16 (permalink) Old 06-28-2019, 03:54 AM
Registered User
 
Join Date: Oct 2015
Posts: 84
Re: 66 Galaxie Gas Cap causing excess tank pressure

Same problem with my 64 Galaxie. I modified a motorad gas cap by reducing the spring tension to the valve so it only keeps a couple lbs. pressure in the tank.
JWSpeed is offline  
post #8 of 16 (permalink) Old 06-28-2019, 05:22 AM
Registered User
 
Join Date: Mar 2017
Location: Portland OR
Posts: 184
Re: 66 Galaxie Gas Cap causing excess tank pressure

I had the same problem on my Ranchero; the pressure got so great that it split the rubber fill hose. I read up on solutions, and many suggested creating a vent line from the top of the tank to the top of the filler hose. But I still didn't see why that would reduce the tank pressure; it just seemed to address the classic 'gas drip' down the fender. I decided to experiment with the cap (O'Reilly #6024) to see if there was a way to make it vented both ways. My understanding is the same as 1964fastback's, that the vent is one way 'in'. I completely removed the plastic vent mechanism and had a good look at what was behind it. I noticed two small rectangular holes to the outside of the sealing edge, and wondered if these could be vents. I set the cap upside down on my bench and poured a little water in the center of the cap. Water flowed out of the two vent holes, indicating vents to the outside.

It now works just as I'd hoped, vented in both directions, without holding pressure. Be aware that there is the chance of a small amount of fuel escaping if driven hard on twisty roads, but it's been 2 years of daily driving, with no gas down the side either.

And I suppose I need to include a disclaimer this day & age: I did this modification at my own risk, and you do it at yours as well.
Attached Thumbnails
Click image for larger version

Name:	blown filler hose.JPG
Views:	33
Size:	88.2 KB
ID:	158231   Click image for larger version

Name:	vent holes.JPG
Views:	34
Size:	62.2 KB
ID:	158233   Click image for larger version

Name:	IMG_6231.JPG
Views:	33
Size:	109.4 KB
ID:	158235  

puttster likes this.

1965 Ranchero Deluxe 66B
Factory 289 4-speed
BrewBoy is offline  
post #9 of 16 (permalink) Old 06-28-2019, 08:22 AM Thread Starter
Registered User
 
Join Date: Nov 2018
Location: Illinois
Posts: 80
Re: 66 Galaxie Gas Cap causing excess tank pressure

To JW: can you explain how I to get at the spring & what you did to change the spring pressure?

To Drew: so all you did was bent the two tabs & remove the center plastic assembly then reinstall the cap?

Sounds like everyone with new caps has an issue with this, wonder why the new replacement caps are designed this way?
7 Litre is offline  
post #10 of 16 (permalink) Old 06-28-2019, 08:59 AM
Registered User
 
Join Date: Mar 2017
Location: Portland OR
Posts: 184
Re: 66 Galaxie Gas Cap causing excess tank pressure

"so all you did was bent the two tabs & remove the center plastic assembly then reinstall the cap?"

Yes.
7 Litre likes this.

1965 Ranchero Deluxe 66B
Factory 289 4-speed
BrewBoy is offline  
post #11 of 16 (permalink) Old 06-28-2019, 01:54 PM
Registered User
 
Join Date: Oct 2015
Posts: 84
Re: 66 Galaxie Gas Cap causing excess tank pressure

Quote:
Originally Posted by 7 Litre View Post
To JW: can you explain how I to get at the spring & what you did to change the spring pressure?

To Drew: so all you did was bent the two tabs & remove the center plastic assembly then reinstall the cap?

Sounds like everyone with new caps has an issue with this, wonder why the new replacement caps are designed this way?
In the Plastic part of the cap there is a two way valve. Springs hold the valves closed. I removed part of the spring so there was very little pressure holding the valves closed. This way no gas will leak out just a small amount of fumes when pressure builds in the tank.
7 Litre likes this.
JWSpeed is offline  
post #12 of 16 (permalink) Old 06-28-2019, 02:44 PM Thread Starter
Registered User
 
Join Date: Nov 2018
Location: Illinois
Posts: 80
Re: 66 Galaxie Gas Cap causing excess tank pressure

Thanks guys for the clarifications! I'll need to take my new cap apart and look into fixing it. Still strange that they make them this way, we shouldn't have to "fix" them to make them function.
7 Litre is offline  
post #13 of 16 (permalink) Old 06-29-2019, 08:59 PM
Registered User
 
Join Date: Oct 2018
Posts: 34
Re: 66 Galaxie Gas Cap causing excess tank pressure

Wouldn't gas just drip out if you had the cap vented both ways and beaned it with a full tank? My Galaxie doesn't seem to build any pressure in the tank but my Volvo 240 does (Converted to gas, still has a diesel tank with no evap or anything) release a lotta pressure when I take the cap off sometimes. I just ignore it. Doesn't seem to hurt anything.

1963 Galaxie 500
1982 Volvo 240 turbo swap
cwazywazy is offline  
post #14 of 16 (permalink) Old 06-30-2019, 05:32 AM
Registered User
 
Join Date: Oct 2015
Posts: 84
Re: 66 Galaxie Gas Cap causing excess tank pressure

Quote:
Originally Posted by cwazywazy View Post
Wouldn't gas just drip out if you had the cap vented both ways and beaned it with a full tank? My Galaxie doesn't seem to build any pressure in the tank but my Volvo 240 does (Converted to gas, still has a diesel tank with no evap or anything) release a lotta pressure when I take the cap off sometimes. I just ignore it. Doesn't seem to hurt anything.
Well in my case the pressure was distorting the tank so much the filler neck of the tank was pushing the fuel door open. IMO, that's way to much pressure in the tank and could cause all kinds of problems. I modified my cap so the valves are still closed, no gas leakage. It just requires very little pressure to open and release the excess pressure. Mine works great, when I remove the cap there isn't any noticeable pressure or vacuum.
JWSpeed is offline  
post #15 of 16 (permalink) Old 07-02-2019, 08:26 AM Thread Starter
Registered User
 
Join Date: Nov 2018
Location: Illinois
Posts: 80
Re: 66 Galaxie Gas Cap causing excess tank pressure

JW, finally got around to prying open my gas cap. Did you shorten just the large spring? If so do you recall how much (removed just one coil)?
7 Litre is offline  
Sponsored Links
Advertisement
 
Reply

Quick Reply
Message:
Options

Register Now



In order to be able to post messages on the Ford Muscle Forums : Ford Muscle Cars Tech Forum forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.

Password:


Confirm Password:
Email Address
Please enter a valid email address for yourself.

Email Address:
OR

Log-in











Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page



Posting Rules  
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On

 
For the best viewing experience please update your browser to Google Chrome