remove the vent guts easily !!!!

not to be a wise guy, but i don't think there's a vent on the john deere tractor i drive, and i fill it to the brim with diesel, no vent trick necessary, sooooo, what do you think the deal is with the vent anyway? don't i remember hissin noises when removing the gas cap in some of the old gassers i used to run? i hear the collision/expansion argument, and it makes sense, but something just ain't addin up in my little brain here. i smell a rat. anyway, i gutted my tdi vent yesterday, easy job done.

deazal,

This ain't a John Deere. The TDI tank has an explansion tube running parrallel to the filler neck.

Without doing the vent trick you cannot reliably fill the fuel to the same place every time.

If you don't fill the fuel to the same place everytime then well you don't really know what kinda of mileage you are getting or when a fuel related problem might start (that results in excessive consumption).

But true - don't do this at the end of the day and leave it parked but the worst is doing this in the morning and leaving the car parked all day in the sun.

I'm tempted to fill up, right to the brim, and then park my car in the sun for a day and see what, if anything, REALLY happens...

What's the worse that could happen? Assuming the fuel expands (how much can 16 gallons of diesel expand, anyway?), where would it come out?

Would it cause any gaskets or lines anywhere to bulge or break? It'd have to be a hot day, too, and we just don't get too many of them in this part of the country.

Probably won't actually do this, but I am curious...

hey i ain't no mechanic, but i do have some common sense, and things ain't addin up. now that 60k john deere sets often in the field on darn hot days in direct sunlight full of fuel with a black fuel tank no less and it ain't got no vent button to top off with and i ain't never even considered it a problem. heck for that matter, would a 5 gallon diesel can blow the stopper out if it sat in direct sunlight full of fuel on a 90 degree day? don't get me wrong, i sure ain't lookin for a cyberbrawl here, just would like some real input as to whether this pressure thing is a valid issue in the tdi or not.

Deazel,

I'm testing this question right now. As I got home this evening, I filled my (vented) TDI to the rim with diesel and then drove 11.3 miles to the house. I have it parked east-west so the sun can bake it all day tomorrow. In the evening I'll let you know if any spilled out.

deazal,

yeah I get your question now.

I'm personally not concerned with the expansion.

Diesel fuel just doesn't compared to Gasoline.

Basically we are using a gas tank instead of a diesel tank.

And yeah. Who hasn't topped their John Deere or Kubota to the complete top and left it sittin in the field or out in the sun by the fuel tank. . .

Diesel expansion is enough to compensate for it by the injection pump but not enough to worry about in the fuel tank.

Its an oil. Pretty stable.

Ok guys I did the vent trick quite some time ago, June 01. I had noticed the the little ball detent thing part of the vent and that it would vent the tank if I pushed it in with fuel nozzle, after investagating I removed it. I had got to thinking about it's fuction. It seems to me to be more of a hangeover from gasser tank. I bet they both use same tank. The gasser would have a return to fuel evap system and TDI doesn't, it vents to ground/air. So to me it seemed the only reason for the vent is hold over from gasser, and so I set about removing it.

I don't buy the crash thing (I could be wrong, but...)that someone else said. I doubt that you would ever have a fire from diesel fuel except in very rare cases. Ooops I'm straying from my story.

Anyway to make a long story short I always fill it till it stops hissing and then fill it up into filler tube (I can see fuel) and stop. On several ocassions it has been done in 112* F sunny weather in Southern NM or OK not to mention a couple of the SE MO days of 100* weather with matching humidity for about a year now, and it has never peepeed on the driveway. Last fill up I almost overfilled and got it to about 1/2 inch from vent and then drove the 15 miles to house and parked in the driveway for two days in 95+ weather and no overflow.

Now the fuel gage reminds me of my old 90 Nissan truck. Fill it then drive it forever before it came off full, then it (Nissan gage) would seem to drop like a rock. I still miss that truck sometimes, even if it did go to shop for warranty work a dozen times. I'm driftinmg again, must be a another senior moment.

So we accept it is a gasser tank apparatus thrown in for manufacturing efficiency?

The air pocket it creates is for what? To handle potential overfill and then expansion?

The valve is opened when you put the cap on so any amount that is in the main fuel line to the fuel tank from "overfilling" can "fall" back towards the fuel tank by the amount of air displaced past the valve as the fuel from the main fuel line settles into part of the air pocket the valve created when it was closed.

The end result being a reduction in any fuel standing in the main fuel line to the fuel tank.

But why? what's the diff? In an extreme case does the tank cap check valve open and let "overfilled and then thermal expanded" fuel flow into the fuel port area and down the little drain line there (where the fuel goes when you try to fully top off and blow it) The drain line comes out in the wheel well?

Does a gasser have the same valve cap we do? They need some kind of vapor trap to prevent the gas from evaporating. Does the cap check valve maintain vapor alone? The fuel cap valve operates to allow air into the tank as it empties via engine fuel consumption. Perhaps it is actually a true check valve and there is no way fuel can get "out" past the fuel cap? Then the air pocket is in fact needed as a pressure relief "accumulator" like on any hot water circuit? In a worst case (cold fuel fully loaded is somehow fantasticly heated prior to any consumption) expansion may slightly pressurize the fuel system causing a blast back when you open it - Is VW trying to save my slacks? An expensive add-on if that's all it is.

Hmmm..........

The truth is out there.

oldnavy, you seem to be confirmin what i was expectin, that i can fill er up to the brim, park it and not worry a bit bout it blowin a cork, and for the explosion on impact theory ala ford pinto, i guess that is plausible but i'm still skeptical. HOWEVER, i just was lookin at my fuel cap the other day and it has a dang warning on it tellin me to not "top off", as though it was a highly dangerous undertaking. i got this gut feeling the old vent switch/gas cap warning may be some lawyer derived liabilty statement or somethin. kinda like the mcd's coffee cup sayin "contents are hot" hehe. what a website we got here, get near 70 posts on the dang fuel vent switch. sheesh!

deazal,

the 'gas cap' is indeed the same part for all VWs.

and I think Frank's warnings are "disclaimer" type things sayin that if you make a mess of your garage or get cited for leakin fuel its your own damn fault

I live a little less than 10km from my regular fuel stop and I will always vent and fill right to the rim. I never once had a problem with fuel spillage or stuff like that and I have a black car. Anyone had a problem with fuel spillage?

I have, a few times when I was trying to be fancy with filling up. If I'm near home, or around Southern Ontario at all, I never need to worry about it.

Oops I wasn't clear enough. I mean fuel expansion spilling caused by venting and leaving it in the sun.

As for spilling while filling, I am guilty almost every time I use the truck sized filler. I still never learned to master it

won't expand enough to spill.

mostly posting as a TTT bump!

This thread rocks!

I'm gonna try de-venting tomorrow, thanks for all the tips!

Originally posted by VW Racer:
Deazel,

I'm testing this question right now. As I got home this evening, I filled my (vented) TDI to the rim with diesel and then drove 11.3 miles to the house. I have it parked east-west so the sun can bake it all day tomorrow. In the evening I'll let you know if any spilled out.

Click to expand...

<font size="2" face="Verdana, Helvetica, sans-serif">I went out to the car at 2:30 when it was well over 100 degrees, had been baking in the sun all day, and the level of the fuel had not moved any visible amount.

My observation is consistent with Chevron's web site http://www.chevron.com/prodserv/fuels/bulletin/diesel/L2_4_6_rf.htm

"THERMAL EXPANSION
Like all liquids, diesel fuel slightly expands in volume as its temperature increases. The coefficient of thermal expansion measures the rate of the expansion. A typical value of the coefficient of thermal expansion for diesel fuel is 0.00046 per degree Fahrenheit. Using this value, 1.000 gallon of diesel fuel at 20°F will expand to 1.037 gallons at 100°F."

Therefore, we can expect a full 16.5 gallon tank to expand to 16.65 gallons as the temp raises from 80F to 100F. This is far less than the approximately 1 liter I consumed simply driving home from the gas station. If you experience a 40F temp raise where you live, 16 gallons (a very nearly full tank!) would expand by about 0.3 gallons -- typically not enough to spill.

Originally posted by VW Racer:


"THERMAL EXPANSION
Like all liquids, diesel fuel slightly expands in volume as its temperature increases. The coefficient of thermal expansion measures the rate of the expansion. A typical value of the coefficient of thermal expansion for diesel fuel is 0.00046 per degree Fahrenheit. Using this value, 1.000 gallon of diesel fuel at 20°F will expand to 1.037 gallons at 100°F."

Therefore, we can expect a full 16.5 gallon tank to expand to 16.65 gallons as the temp raises from 80F to 100F. This is far less than the approximately 1 liter I consumed simply driving home from the gas station. If you experience a 40F temp raise where you live, 16 gallons (a very nearly full tank!) would expand by about 0.3 gallons -- typically not enough to spill.

Click to expand...

<font size="2" face="Verdana, Helvetica, sans-serif">I agree that it is very very remote that the would be a spill, however VW has to assume that Mr. Elmer Fudd will fill it right to the brim on a subzero day then roll it into his heated garage and let it sit for two days. When there is a drop or anything that goes wrong then VW assumes it will be sued for Millions of $$.

Thats no doubt the reason for VW's CYA with the air pocket.
Also the air can be compressed to a certain degree. So when Elmer does this trick the air can absorb the incresed volume.
If Elmer does this with no air pocket it could stretch the plastic tank. If the is a weak spot any where it could let diesel fuel out.
There may be other reasons for VW's thinking too.

I think 99.99% of us are savvy to this. its the .1% that could get hurt.

If the fuel tank were spherical and rigid, fuel expansion could be a problem.

But the fuel tank is not perfectly rigid and it is rectangular. It is held in by straps. The tank can and most certainly does flex and bulge with fuel load, which would include the anomalous thermal expansion. The 0.3 gal is not much at all for the tank to 'bulge' a bit.

Also, underground fuel storage tanks are at pretty constant temps, something like 55-60F. Just a couple feet below the surface, the ground temp stays quite constant.

And then even if you did fill to the brim, how do you know you got all the air pockets out? Fill to brim and then check when you get home..... is the fuel still at the very brim? Even if you live close to the filling station, the jostling on the way home prolly would feed any trapped air to the filler neck.

I have vented the tank a few times in the past and filled it up till I can see diesel in the filler neck. I drove for about 5 miles to get home and parked it outside for a few hours straight.. never had a problem with diesel overflow at all.

I always vent, in fact I've removed the vent valve altogether.



Filled the other day about 10 AM, and drove the little over one mile distance home. Had collected a small sample for viewing in a plastic bottle.

Parked the Wagon in the hot sun and filled the neck to running over, cleaned up everything really well and screwed the cap on tight. Several hours later at about 3 pm, I went out and slowly loosened the cap, and guess what? It was still full of course, but there was no expansion or had there been, no running over, and no problems. It had to be at least fifteen degrees warmer by that time.



I'm no scientist, but it would seem to this writer that worrying about there being problems after 'venting' with the tank being too full is simply worrying about nothing.

Your mileage and opinions may vary.

Just did the ventectomy today -- it was a piece of cake! Took me about 10 minutes as I was taking my time, and also had to orient myself to see where I was supposed to pry. It helps to have two screwdrivers, one to pry in the tab and the other to push the vent release button towards the rear of the car.

Now I just have to wait till my next fillup to try this out... I still have half a tank of fuel left.

Just started to do this happy vent thingy. I after I removed the torx screw I gently pulled on the housing around the fuel filler. The whole fuel lid and came off and there is this tube going somewhere. Does the other end of this clear tube go anywhere? or connect to something?

Thank You
dzlbug

Originally posted by dzlbug:
Does the other end of this clear tube go anywhere? or connect to something?

Click to expand...

<font size="2" face="Verdana, Helvetica, sans-serif">That is the fuel overflow "exit" tube; it doesn't clamp on anywhere. It just dangles around the rear fender/quarter panel area.

Thank you
one Ventectomy is completed on this needo car.
time to go drive around now..

Has anyone done this on A2/3s or B4s?

lrpavlo did it on a B4 . . . I think DBW has done it on his A3 . . .

The whole fleet has vent surgery done

Originally posted by TDIBill:
Has anyone done this on A2/3s or B4s?

Click to expand...

<font size="2" face="Verdana, Helvetica, sans-serif">See my post on page 3 for doing this on a B4. Could be the easiest body style to do this to.

I performed surgery this morning. It took 5 minutes and was easy as pie.

A note... a couple of people have mentioned having to push HARD on the little black vent tab to get the white valve assembly to pop out. This shouldn't be necessary.

If you look at the black housing to the aft of the filler neck, there is a notch cut in the bottom, and you can see the white valve through the notch. This is an access hole for a retaining tab. Take a flathead screwdriver, push up on the white valve through this notch, and you should be able to push the black vent tab with your finger and the white valve will disengage and slide right out. This step is shown in GeWilli's instructions on his page... a picture says "push here" or somesuch.

When you take the "vent guts" out of the white valve (I reinstalled the spring and the clip after taking out the vent tab), reinstall the valve! Make sure that it's oriented correctly, and it should *SNAP* into place when the retaining tab locks in.

-davin

Thanks, first actual mod was a success!
preciate the tip