So I was doing a small bit of reading about fuel tank caps...it appears that diesel engines need caps with a vent of some kind. This is certainly news to me.

What are you guys' opinions on why this is ?

Quite a while back, I replaced my cap with a generic locking one. Don't recall if it was vented or not...probably not. Might this be the cause of this mysterious "Water in Fuel" light that comes on sporadically at idle (almost never at cruising speed) when there is no water in the fuel, and a clean filter is in place ?

I just drove home with the cap off. The light came on a tiny bit here and there, but not as much as usual...

TIA.

diesel is more like oil, and gas is more like, well, gas....as in vapor.

a non vented cap can collapse a tank in a diesel truck. the pumps keep pumping and eventually collapse the tank.

Not to mention its hard on lift pumps and IP's

You cant vent a gas tank cause it will evaporate into the air, i have this problem with my fuel cell in my Jeep. It always stinks, esp with the top on, i have the cell behind the back seat. Im still looking for a way to vent it properly.

This post has me thinking...I have an 82 6.2L that I picked up this summer. Both fuel caps say "Diesel Fuel Only" on them but I have noticed that when I go to fuel up the truck, after it has been running for a while, that there is a vaccum on the tank. I so far have brushed it off to a plugged tank vent.

Do the tanks on these trucks even have vents, or are there just supposed to be vents built into the caps?

Besides the obvious pump stresses that a vaccum in the tank will create, are there any other immediate adverse drivabilty affects?

If you loose fuel pressure, you can loose power. If fuel pressure/flow is too low, that can damage the IP over time.

Seanb23, check your fuel pressure. The WIF light can come on when the fuel pressure is too low, there is a pressure sensor in the fuel filter to indicate that.