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Discussion Starter #1
After replacing with a new diesel cap I am still getting a noticeable whoosh when I open the fuel cap. Is there a modification to the cap itself to fix this issue. Or is there something wrong with the venting system?


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The cap is the venting system. I drill a tiny hole in the cap to bypass the valve and never worry about it again. Hole is on the inside and does not exit the exterior part.
I had a stuck cap collapse the fuel tank, on vacation of course.
 

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There is a small rubber valve on the underside in the cap, just remove it.
I did that on all my trucks.
The black top of the cap snaps over the white insert and can be separated by prying the tabs in the cap away to the outside one at the time and lifting up on the insert.
 

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The cap is the venting system. I drill a tiny hole in the cap to bypass the valve and never worry about it again. Hole is on the inside and does not exit the exterior part.
I had a stuck cap collapse the fuel tank, on vacation of course.
That is what I did too. No more worries.:bounce:
 

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Does it matter exactly where to drill hole or anywhere on the inside part?
 

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This works. Hole could be smaller, that bit was already in the drill.

FuelCapMod.jpg
 

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Thanks exactly what I wanted!
 

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Why does everyone care about a little noise enough to risk fuel contamination??? It's not like the fuel is so full when you take the cap off that it could spray out - the tank is nearly empty, and it vents while you're unscrewing the cap.
 

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Why does everyone care about a little noise enough to risk fuel contamination??? It's not like the fuel is so full when you take the cap off that it could spray out - the tank is nearly empty, and it vents while you're unscrewing the cap.
See glagulators post #2. It also allows the fuel pumps to function more efficiently.
 

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Why does everyone care about a little noise enough to risk fuel contamination??? It's not like the fuel is so full when you take the cap off that it could spray out - the tank is nearly empty, and it vents while you're unscrewing the cap.
It's not the fuel contamination, it is excess vacuum you have to worry about.
Excess tank vacuum is hard on the IP and the LP and can cause a tank to collapse.
 

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I thought the issue was a little PRESSURE in the tank. If you have a cap that doesn't vent properly, replace it.
 

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I thought the issue was a little PRESSURE in the tank. If you have a cap that doesn't vent properly, replace it.
A little pressure helps push fuel to the IP which is in principle not bad.

No need to buy a new cap, just take the cap apart and clean it, usually lots of dirt buildup inside prevents venting
 
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Yeah, I meant not venting to let air IN as the fuel goes out, which would cause the vacuum you said was the issue. In that case, I'd just replace the cap - they're not expensive, even for the locking one I had.

I initially though pressure in the tank was the OP's complaint. That's why my first response was "who cares?"
 

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Discussion Starter #14
Thanks for all the replies folks. Brand new diesel cap wasn't venting so I drilled a hole in it and all is well. No more issues.


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Yeah, I meant not venting to let air IN as the fuel goes out, which would cause the vacuum you said was the issue. In that case, I'd just replace the cap - they're not expensive, even for the locking one I had.

I initially though pressure in the tank was the OP's complaint. That's why my first response was "who cares?"
Why buy a new cap, might as well throw your money into the river, same thing.

The biggest issue is, most caps are for gassers and even the diesel ones are the wrong ones, which you have to modify anyway, so now your spending money to mod a cap, :confuzeld
 
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I have to chime in. I just had a sputtering issue a few days ago. I unscrewed my "diesel" fuel cap and didnt hear the vacuum release. This helped me easily diagnose my pre lp filter was plugged (no tank sock) causing too much restriction for the lp to pull the fuel. So this actually helped me diagnose the run issue. I suppose if my return was plugged this could have caused the same result but doubtful. Still I was able to open my t valve and see hardly any flow to tip me off. I say get the correct cap with no extra venting. I have 5 diesel vehicles all with no mods to the caps and no problems. The stress caused to the lp is debatable.
 
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