Is having a small amount of back pressure when removing the fuel cap normal or indicative of a problem?
Fuel Tank Pressure
- Thread starter Gun Runner 5
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I would say a small amount would be ok, but possibly indicative of a vent plugging up.
I definitely get some negative pressure removing the fuel cap on my '90 hzj75.
Is it gas or diesel?
Gas systems sometimes have canisters for the fumes which are vented actively when getting signal to do so to the solenoids....
If regular vent (like diesel) can be starting to clog.
If negative pressure, also might be slightly clogged, but some (on emission controlled vehicles) is usually natural.
Also depends on ambient temp's obviously....
So, some food for thought
Good luck
- Thread starter
- #5
Diesel
Yup - mine's diesel too. Now I'm kind of curious if I get it in both tanks or just one, but I don't recall. Which vent is the one that's likely to clog? I'm doing a pretty big refresh on my troopy. Maybe I should add fuel hoses / vents to my list.
There’s what looks like a small engine fuel filter as part of the vent system that is at the top of the filler. If that gets plugged then it would most likely cause a pressurized condition
You got me curious too......
Mine is a 1hz.
I am not that proud for it, but I own the vehicle for almost a year and still on my first tank......
So do not think I have encountered this phenomenon.
I am interested in this though
You have either incredible fuel economy, or you do not use it.... I am lucky if I can get a tank to last 2 weeks.... 😒You got me curious too......
Mine is a 1hz.
I am not that proud for it, but I own the vehicle for almost a year and still on my first tank......
So do not think I have encountered this phenomenon.
I am interested in this though
Haha, you are correct, I am not using it too much as it is recreational only, it is not quite baselined yet, and I am afraid of the number on the pump when I do go to fill it up.....
I though a bit of negative pressure proves you have no leaks in the fuel line and tank? Kind of thought it was healthy, like a bit of vacuum= no water/moisture ingress?
Well, vacuum in the tank proves (sort of) it to be sealed, thus getting fuel out to the engine through the hoses and not getting anything in, to take its place.
However
A. This means that the pump would need to overcome ever-growing negative pressure until it would starve the engine.
B. The existing vacuum will happily suck anything it can "get its hands on" from any crack or untighten hose. That means dust and water getting more easily into the tank.
So, negative pressure in not good and is supposed to be handled by the regular vent (at least in the diesels).
Positive pressure is allowed to some extent and is being release every once in a while, while the vehicle is operated by the controlled vents into the canister, on the gasoline (emissions controlled) vehicles
And by small orifice filtered vents on the diesels.
This is my understanding of the subject.
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Well I should qualify my previous statement - I do often get some pressure change (a hiss) when removing the cap. Most apparent when I stop to fill up after a longish drive. It seems like it is negative pressure (i.e. vacuum in the tank) but I haven't tried to confirm that. Maybe it's positive pressure.
I will start putting my nose next to the filler when I remove the cap and see if it feels like fumes coming out or air rushing in
I will start putting my nose next to the filler when I remove the cap and see if it feels like fumes coming out or air rushing in
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Well there ya go!
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What Is a Diesel Tank Breather and Why Is It Important? - Banlaw
There are several steps a business can take to ensure the safety and cleanliness of fuel stores; these range from fuel sampling, scrubbing, and stock rotation to the regular maintenance of fuel storage tanks. Regardless whether you are trying to maintain a bulk fuel storage tank or tank farm, or...
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