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Holset
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Joined: April 21, 2008
Posts: 193
Location: Memphis, TN
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 Posted: Fri Jun 18, 2010 8:36 am Post subject: Fuel tank pressure build up |
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I have a 1969 bus, that when I open the gas cap I get a rush of air. I have replaced the usual fuel lines, but just havent seen this before with my other bus(s). Ideas???
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aeromech
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Location: San Diego, California
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| Posted: Fri Jun 18, 2010 8:43 am Post subject: |
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Do you mean positive pressure or negative pressure?
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Holset
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Joined: April 21, 2008
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Location: Memphis, TN
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| Posted: Fri Jun 18, 2010 9:05 am Post subject: pressure |
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Positive pressure. As if the tank is not venting.
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'72 Sunroof Deluxe "Hippie" the bus
'75 FI 1600 Std Bug "Bob" the bug (sold)
'69 Campmobile "Otter bus"
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aeromech
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Joined: January 24, 2006
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Location: San Diego, California
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| Posted: Fri Jun 18, 2010 9:13 am Post subject: |
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So, just like the fuel tank for my outboard motor, your tank builds pressure because of being exposed to warm temperatures. I'd say your vent system isn't working. Didn't you say you worked on that? You must have got it wrong somehow. I'm not being much help here, I know.
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Lead Mechanic: San Diego Air and Space Museum
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Boeing 727,737-200-300-400,757,767
Airbus A319,320,321
DC9/MD80
BAe146
Fokker F28/F100
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VW Type 2 1971 (3 ea.) 1978, 1969
VW Jetta
VW Passat
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Holset
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Joined: April 21, 2008
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Location: Memphis, TN
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| Posted: Fri Jun 18, 2010 9:41 am Post subject: pressure |
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Ran all the lines, and did not encounter any blockages.
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'72 Sunroof Deluxe "Hippie" the bus
'75 FI 1600 Std Bug "Bob" the bug (sold)
'69 Campmobile "Otter bus"
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aeromech
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Joined: January 24, 2006
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Location: San Diego, California
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| Posted: Fri Jun 18, 2010 10:25 am Post subject: |
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This tank is out of a 1968 bus
you can see the vent towards the top front of the tank. If that's clear there is no way for the tank to build up pressure. If I remember right the line runs up to the filler door.
you can see it in this pic
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Licensed Pilot (Single engine Land)
Boeing 727,737-200-300-400,757,767
Airbus A319,320,321
DC9/MD80
BAe146
Fokker F28/F100
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VW Type 2 1971 (3 ea.) 1978, 1969
VW Jetta
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70Crew
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Joined: June 12, 2006
Posts: 776
Location: Grand Rapids, MI
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| Posted: Mon Sep 03, 2018 2:58 pm Post subject: Re: Fuel tank pressure build up |
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Anyone else getting this? Stock 1970 crew cab. I filled the tank and drove about 75 miles. The outside temperature was about 75 degrees F. I did not park it anywhere and it was overcast. When I got home I heard a strange noise and figured out that pressure (a lot) had built up in the tank. I replaced all the fuel, vent and charcoal canister hoses when I restored the bus. I believe the gas cap is original; I assume that the stock 1970 cap isn’t vented in any way, correct?
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70Crew
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Location: Grand Rapids, MI
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| Posted: Mon Sep 03, 2018 3:01 pm Post subject: Re: Fuel tank pressure build up |
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As I think through this without access to the bus, does the tank vent through the charcoal canister? If so, I wonder if that could be plugged up?
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SGKent 
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Location: Citrus Heights CA (Near Sacramento)
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| Posted: Mon Sep 03, 2018 4:48 pm Post subject: Re: Fuel tank pressure build up |
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I think this is an early bay. Maybe a bug plugged the vent with mud. do you have a vented cap?
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70Crew
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Joined: June 12, 2006
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Location: Grand Rapids, MI
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| Posted: Mon Sep 03, 2018 4:52 pm Post subject: Re: Fuel tank pressure build up |
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Definitely not a vented cap.
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busdaddy
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| Posted: Mon Sep 03, 2018 5:01 pm Post subject: Re: Fuel tank pressure build up |
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If you have a charcoal canister the tank vents though that (or should), try blowing into the little nipple on it as well as the hose that connects to it.
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Amskeptic
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Joined: October 18, 2002
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| Posted: Mon Sep 03, 2018 5:18 pm Post subject: Re: Fuel tank pressure build up |
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| 70Crew wrote: |
| As I think through this without access to the bus, does the tank vent through the charcoal canister? If so, I wonder if that could be plugged up? |
Yes, 1970 does not have a vented cap. You can blow through all of the lines in question to test.
a) remove 12mm hose from fan housing nipple and blow through it and the charcoal tank, you should feel air at the hose from the tank that goes into the air cleaner.
b) remove small hose from charcoal tank and blow firmly into tank. See if there is a difference with cap on vs off.
Colin
(NaranjaWesty has a restrictor in the fuel vapor line to charcoal tank, a little white plastic restrictor that I can imagine plugging up rather easily)
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70Crew
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Joined: June 12, 2006
Posts: 776
Location: Grand Rapids, MI
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| Posted: Tue Sep 04, 2018 5:51 am Post subject: Re: Fuel tank pressure build up |
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It may take a day or two but I am on it.... thanks gentlemen! I will report back with my findings.
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Spike0180
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Joined: June 06, 2015
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Location: Detroit, Michigan
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| Posted: Tue Sep 04, 2018 6:06 am Post subject: Re: Fuel tank pressure build up |
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Check to make sure none of those vent hoses are pinched or kinked too. I'd think that would be a likely culprit. My 1970 does not do this.
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