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Old 06-03-2023, 07:56 PM   #1
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fuel tank has a vacuum

My issue is that my fuel tank (2007 Dutch Star 4320) has a large vacuum on it when opening the fuel cap for refueling. It sucks outside air for 45 seconds or so when unscrewing the cap on 1/2 empty tank from full. also, the AquaHot heater will not operate, relieve the vacuum it works. My actions to date: 1. At the super Tampa RV show I visited the Spartan chassis booth and talked with a factory guy about the issue. His response was plug hose or bad valve on top of tank. OK 2. I took the RV to my local shop in Northern Ohio and ask him to check this out. He said that the pressurized with compressed air and air has coming out of the vent hose. My RV shop asked me to contact Spartan about this issue. Spartan tech service said NO VALVE on top of tank for venting. Man I'm confused? More background info: the coach is new to me, only 1 year. Has only filled the fuel tank 3 times with the vacuum upon release of the fueling cap...I now leave it loose so it doesn't seal. So, my question is does a 2007 K2 Spartan chassis have a valve for venting? if it does how does it work? Anybody else had/have this problem. Sorry for the long post, but wanted to give all the info
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Old 06-03-2023, 08:09 PM   #2
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I'll chime in. I have no experience with your chassis but is your fuel cap supposed to be vented?
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Old 06-03-2023, 08:52 PM   #3
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The tank has to be vented, whether it has an actual vent or vented cap(s). Gas tanks are vented to a carbon filter.
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Old 06-03-2023, 09:34 PM   #4
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Can you contact Spartan and get a part number and supplier for the fuel caps to make sure you have the correct ones on the coach.

My DSDP on Freightliner with Cat engine uses unvented caps and the tank pressurizes as hot fuel is returned to the tank from the engine .
BIG note on the fuel door to remove the cap SLOWLY .

Spartan Motorhome support ; Have your chassis serial number handy .

1-800-543-4277
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Old 06-04-2023, 04:23 AM   #5
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Quote:
Originally Posted by Skip426 View Post
Can you contact Spartan and get a part number and supplier for the fuel caps to make sure you have the correct ones on the coach.



My DSDP on Freightliner with Cat engine uses unvented caps and the tank pressurizes as hot fuel is returned to the tank from the engine .

BIG note on the fuel door to remove the cap SLOWLY .



Spartan Motorhome support ; Have your chassis serial number handy .



1-800-543-4277

Maybe the OP assumes itís vacuum be really is releasing pressure.

That being said. If more fuel is being burned than is returning it seems there would eventually be a vacuum, if no vent, especially as the fuel cools down.
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Old 06-04-2023, 11:18 AM   #6
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Originally Posted by Rob_M View Post
Maybe the OP assumes itís vacuum be really is releasing pressure.

That being said. If more fuel is being burned than is returning it seems there would eventually be a vacuum, if no vent, especially as the fuel cools down.
I've run my fuel down to the warning light and always had pressure ( although I've never opened the fuel cap before starting in the morning ) , even with a short morning run to fuel up , the tank has built up pressure.

OP ; stated ; " Aqua hot won't run until vacuum released " I doubt the Aqua hot would react that way to fuel tank pressure .
Could this be an issue with the hydro hot fuel pump ?
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Old 06-04-2023, 01:49 PM   #7
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I would replace the filler caps. They are cheap.
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Old 06-05-2023, 06:32 AM   #8
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Quote:
Originally Posted by Skip426 View Post
Can you contact Spartan and get a part number and supplier for the fuel caps to make sure you have the correct ones on the coach.

My DSDP on Freightliner with Cat engine uses unvented caps and the tank pressurizes as hot fuel is returned to the tank from the engine .
BIG note on the fuel door to remove the cap SLOWLY .

Spartan Motorhome support ; Have your chassis serial number handy .

1-800-543-4277
I have called Spartan, the parts guy said, I'm parts you need to talk with tech service. Tech service said no valve on top of the tank, but it vented. It is a vacuum, NOT pressurized...the cap gets sucked in towards the tank, not push out towards the fuel door. My 31 years in business diesel shop said there should be a rollover valve on top of the tank.
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Old 06-05-2023, 06:45 AM   #9
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Quote:
Originally Posted by Skip426 View Post
I've run my fuel down to the warning light and always had pressure ( although I've never opened the fuel cap before starting in the morning ) , even with a short morning run to fuel up , the tank has built up pressure.

OP ; stated ; " Aqua hot won't run until vacuum released " I doubt the Aqua hot would react that way to fuel tank pressure .
Could this be an issue with the hydro hot fuel pump ?
the AquaHot GURU in Colorado said the Dutch Star 4320 have issues with sucking fuel from the tank. I have spent hours bench-testing my AH unit. it sucks fuel fine, but this is a strong vacuum. pulled in for the night, turned on AH didn't fire, then timed out, turned off AH, and repeated the same results. In the morning remembered the tank vacuum issue, and opened the cap to relieve the vacuum in the tank...AH fire up and perform fine. just my experience.
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Old 06-05-2023, 07:41 AM   #10
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fuel tank has a vacuum

Quote:
Originally Posted by oldeguy View Post
the AquaHot GURU in Colorado said the Dutch Star 4320 have issues with sucking fuel from the tank. I have spent hours bench-testing my AH unit. it sucks fuel fine, but this is a strong vacuum. pulled in for the night, turned on AH didn't fire, then timed out, turned off AH, and repeated the same results. In the morning remembered the tank vacuum issue, and opened the cap to relieve the vacuum in the tank...AH fire up and perform fine. just my experience.


Sounds like youíre definitely on top of the problem. Hopefully someone will answer your vent questions. As a temporary fix you could drill and tap one filler cap and install a small vent/filter. Or a 1-way check valve.
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Old 06-07-2023, 11:17 AM   #11
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fuel tank vacuum

hello all Dutch Star owners, I've got a 2007 DS 4320 that develops a strong vacuum in the tank as fuel gets used during driving. IE, start with a full tank then at re-fueling time, about 1/2 tank of 70 gallons used. when I start to unscrew the cap it felt funny as I was unscrewing. the tank had a strong vacuum that lasted 30 to 45 seconds. I don't think it should do this. I need suggestions on what potential solutions to fix this issue.

Bit more background. This coach is new to me 72K miles, only 6 fill-ups with fuel caps tight (sealed) I've been leaving the caps loose on other fill-ups. I've talked with Spartan Chassis about this issue of the vacuum in the tank...the tech dept. say it's a plugged vent line, parts guy says no valve on top of tanks. My mechanic said he pressurized the tank and the vent was flowing air. BTW, also posted on the Spartan Chassis page.

I don't know what to think...I'm grasping for straws at this point. (american slang)
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Old 06-07-2023, 12:19 PM   #12
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Quote:
Originally Posted by oldeguy View Post
hello all Dutch Star owners, I've got a 2007 DS 4320 that develops a strong vacuum in the tank as fuel gets used during driving. IE, start with a full tank then at re-fueling time, about 1/2 tank of 70 gallons used. when I start to unscrew the cap it felt funny as I was unscrewing. the tank had a strong vacuum that lasted 30 to 45 seconds. I don't think it should do this. I need suggestions on what potential solutions to fix this issue.

Bit more background. This coach is new to me 72K miles, only 6 fill-ups with fuel caps tight (sealed) I've been leaving the caps loose on other fill-ups. I've talked with Spartan Chassis about this issue of the vacuum in the tank...the tech dept. say it's a plugged vent line, parts guy says no valve on top of tanks. My mechanic said he pressurized the tank and the vent was flowing air. BTW, also posted on the Spartan Chassis page.

I don't know what to think...I'm grasping for straws at this point. (american slang)
You can always purchase a Vented Fuel Cap.
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Old 06-07-2023, 01:03 PM   #13
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Quote:
Originally Posted by oldeguy View Post
hello all Dutch Star owners, I've got a 2007 DS 4320 that develops a strong vacuum in the tank as fuel gets used during driving. IE, start with a full tank then at re-fueling time, about 1/2 tank of 70 gallons used. when I start to unscrew the cap it felt funny as I was unscrewing. the tank had a strong vacuum that lasted 30 to 45 seconds. I don't think it should do this. I need suggestions on what potential solutions to fix this issue.

Bit more background. This coach is new to me 72K miles, only 6 fill-ups with fuel caps tight (sealed) I've been leaving the caps loose on other fill-ups. I've talked with Spartan Chassis about this issue of the vacuum in the tank...the tech dept. say it's a plugged vent line, parts guy says no valve on top of tanks. My mechanic said he pressurized the tank and the vent was flowing air. BTW, also posted on the Spartan Chassis page.

I don't know what to think...I'm grasping for straws at this point. (american slang)
I think the tank vent lets the pressure out of the tank as the fuel heats up but itís not a breather, to let air into the tank. The one way valve should be in the cap to let air in as a vacuum is formed from the fuel cooling or being used.
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Old 06-08-2023, 11:22 AM   #14
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I'd say something isn't working correctly. A fuel tank is vented to allow air into the tank as the pump pulls the fuel out. This is so that the tank doesn't collapse from the vacuum. I suspect your vent is clogged. I would try a vented fuel cap first because trying to troubleshoot the vent can be a PITA.
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