just got a new locking gas cap from napa. double checked and made sure it was the one for the diesel.

well when i remove the cap, there is some hissing from vacuum. not much, but a little. it's not supposed to do that right? or some vacuum is ok? I'm not totally clear on this, even after reading a bunch of posts about it.

it's a mostly full tank, and it's in the 70s here right now.

Thanks.

just got a new locking gas cap from napa. double checked and made sure it was the one for the diesel.

well when i remove the cap, there is some hissing from vacuum. not much, but a little. it's not supposed to do that right? or some vacuum is ok? I'm not totally clear on this, even after reading a bunch of posts about it.

it's a mostly full tank, and it's in the 70s here right now.

Thanks.

Diesel caps are designed to allow a little vacuum, 2hg i believe. Its not air tight like a gasser. If it's for a diesel, you're ok. If it says Diesel Fuel only even better.

I always have some hissing like you described with the factory cap as well as with an aftermarket diesel specific fuel cap, so in my opinion that it is normal, at least it has never caused me any trouble. If the vacuum built up to an unacceptable point you would have performance issues, if you have any issues loosen the cap first thing and if they go away it was too much vacuum and you may want a different cap. But my guess is your okay.

Thanks,

Mine would still have a little hiss with the factory cap. Is started not tightning the cap all the way to eliminate any vacuum.

My factory cap always hissed a little - last year, when Diesel prices
made a full tank worth 140.00, I decided it needed a lock.
Couldn't find a Diesel locking cap, got a gasser from Autozone,
and removed the big O-ring - now no vacuum & no pressure on tank :)

Diesel caps are designed to allow a little vacuum, 2hg i believe. Its not air tight like a gasser. If it's for a diesel, you're ok. If it says Diesel Fuel only even better.


this is correct.

- last year, when Diesel prices
made a full tank worth 140.00, I decided it needed a lock.
Couldn't find a Diesel locking cap, got a gasser from Autozone,
and removed the big O-ring - now no vacuum & no pressure on tank :)
So if I remove the O RIng I will have a locking diesel cap. I never thought of that.

I got a locking gas cap at Wally World of all places for a diesel,... just cross ref. the numbers for stant and you'll find it... IIRC it was about 1/2 the price of autozone/napa/and the others... my good luck..

ok well i guess i'll run it and if i don't have any issues then i'll just leave it alone! thanks.

Needs some vacuum to keep the diesel from foaming up too bad. Too much is bad, but a little is normal.

Needs some vacuum to keep the diesel from foaming up too bad. Too much is bad, but a little is normal.

Had no issues with mine in the last year

Anybody with a stant part #? I have a LMM