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TDI Fuel Economy Discussions about increasing the fuel economy of your TDI engine. Non TDI related postings will be moved or removed.

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Old February 17th, 2012, 15:46   #1
LMJ
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Default How many gallons

How many gallons does your mk4 golf take to fill when fuel buzzer sounds. Mine is 12.5.

Does glow plug issue reduce fuel mileage
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Old February 17th, 2012, 16:14   #2
tditom
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That sounds extrememly low. Do you fill to the brim and vent when you fill?

That car can hold over 17 gallons when vented.
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Old February 17th, 2012, 17:29   #3
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My 2001 Jetta TDI takes about 12.25 gallons to fill after the warning light comes on, and then driving about 25 additional miles. That's with filling to the brim...
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Old February 17th, 2012, 18:12   #4
MikeMars
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You could probably do another 50 or 60 miles before running out (but it's impossible to know without finding out the hard way, which is really not a good idea at all).

You mention brimming, but do you vent as well?
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Old February 17th, 2012, 18:25   #5
c2020again
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Please explain venting. Is it possible to vent a 2001 Jetta? I don't see any valve as mentioned on other posts. Maybe a PO removed mine.
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Old February 17th, 2012, 18:33   #6
MikeMars
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Basically fuel tanks which are shared with the petrol version of the vehicle have an expansion chamber to capture the petrol vapour on hot days & feed it out so that the fuel doesn't overflow. There is a pipe from the expansion chamber to a valve just inside the filler cap. When the cap screws in, it opens the valve and the vapour is free to move up & the liquid fuel to move down.

So venting consists of pressing this valve in some way to let the air escape when refuelling. This is safe on a diesel because diesel doesn't turn into vapour on hot days.

Some cars have the expansion chamber & others don't. All mine have had it (the vento, the A4, the Passat & the A2). But if you don't see the valve then you might have one of the ones without. If someone has already removed the valve, then there should still be a visible hole there instead.
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Last edited by MikeMars; February 17th, 2012 at 18:39.
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Old February 17th, 2012, 18:38   #7
tditom
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Quote:
Originally Posted by c2020again View Post
Please explain venting. Is it possible to vent a 2001 Jetta? I don't see any valve as mentioned on other posts. Maybe a PO removed mine.
There is a vent valve that is closed when you have the fuel cap off. This is an artifact from the gasser design where it is needed because gasoline expands greatly when external temps heat up. Diesel does not need this safety feature.

When this valve is closed a pocket of air is trapped in the expansion tank. Opening the valve allows the expansion tank to fill with fuel, but is tricky to do when you are filling the tank. You can hold the valve open with the top of the fuel dispensing nozzle, but it is difficult. You can also alterate between topping to the brim and then opening the valve. The easiest way is to remove the valve (aka ventectomy). You can then fill to the brim easily.

If you really only get 12.5 gal while venting after the low fuel warning goes off, then it is set to trip at around 4.5 gal. It's supposed to be around 1.9 gal.
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Old February 17th, 2012, 18:39   #8
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I asked the question because my fuel mileage seems low, so i was thinking that the fuel pump reading was off. I use the same pump for each fill up.
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Old February 17th, 2012, 18:42   #9
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Quote:
Originally Posted by tditom View Post

If you really only get 12.5 gal while venting after the low fuel warning goes off, then it is set to trip at around 4.5 gal. It's supposed to be around 1.9 gal.
i don't vent. except i'm about to if this thread is hijacked any further.
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Old February 17th, 2012, 18:46   #10
tditom
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Quote:
Originally Posted by LMJ View Post
i don't vent. except i'm about to if this thread is hijacked any further.
hijacked?
When discussing fuel tank capacities (such as how much you need to top off after the warning come on), it is pointless to discuss without considering venting. Venting is the only way to ensure you are filling to the same level each time. It gives you more accurate per tank mpg in addition to max range. Why wouldn't anyone choose to vent their tank?
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Old February 17th, 2012, 18:51   #11
tditom
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Quote:
Originally Posted by LMJ View Post
...
Does glow plug issue reduce fuel mileage
not a measurable amount
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Old February 18th, 2012, 07:08   #12
VWBeamer
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Quote:
Originally Posted by LMJ View Post
How many gallons does your mk4 golf take to fill when fuel buzzer sounds. Mine is 12.5.

Does glow plug issue reduce fuel mileage
The glow plugs can misfire, I would check your coils, wires and distributor also....and make sure the Carb is clean.

When the last time you checked your TB ( Turbo Belt) make sure it's tight, it could be slipping.
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Last edited by VWBeamer; February 18th, 2012 at 07:12.
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Old February 18th, 2012, 07:11   #13
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I was going to tell you that my wagon holds 16 gallons when the light goes on, but I vent and I would not want to hi jack your thread.
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Old February 18th, 2012, 15:56   #14
MikeMars
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Quote:
Originally Posted by tditom View Post
hijacked?
...
I think he's joking since a) it's a pun, and b) it obviously is relevant to his thread. Although it can be hard to tell over the net.

It's a good point about the low-fuel light possibly coming on early - on one of my cars the light used to come on just as it was about to run dry (between 2 miles & 20 miles), so the opposite can probably also be true.
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Y2000 Passat TDi 115 PD RETIRED, M5, Best 75MPGuk, usually 60-70. 900m clubx7. 1000 mile clubx3.
VW Fuel saving tips

Last edited by MikeMars; February 18th, 2012 at 16:00.
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Old February 18th, 2012, 16:28   #15
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VWbeamer.....lol...i can't stop laughing...better check the Halogen fluid as well eh!
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