glow plug light flashing, then stays on

[92EcoDiesel Jetta]

I am driving and saw the glow plug light flash on and off then constant on. I pulled over and checked glow plug wires w volt meter and there was no voltage (LED on). Is that some kind of warning or something flaky with the glow plug relay?

[stewardc]

That's normally the indicator for water in the primary "catch basin" under the car.

[92EcoDiesel Jetta]

Holy crap! Where is this catch basin exacly and what tools do I need to drain it?

[stewardc]

Right rear, just ahead of the rear wheel. There's a knob on the bottom and that's the valve. Open it up and drain it into a catchcan.

[92EcoDiesel Jetta]

Thanks! Found it in the Bently also. I drained about a cup and the light is out for now. I will let it settle and look for signs of water later. It's great to have a water catch basin & drain on the bottom near the tank, far away from the fuel filter. Would you know what type of water sensor it uses? Is there an amplifier or circuitry associated with it?

[stewardc]

I just know it's very simple and normally has to be replaced at 400,000km 

[92EcoDiesel Jetta]

the light went off only temporarily and came back on. I drained more (another cup) fuel out and it did the same thing. I will drain more tomorrow and see what happens. There were no visible signs of water. Maybe the WIF sensor is flaky and needs replacement?

[SolarSteve]

Mine did that constantly.  It would flash slow, fast or just stay on for a while.  I drained fuel MANY MANY times and never got any water out of it and it never made it any better.

A few months ago I decided to drop it to try to clean it out and in the removal process I broke one of the plastic nipples so I did not reinstall it, I cut the wires and connected the fuel lines.

Inside of the separator was a brownish slimey gunk that I assume was the problem.

Anyway, my fuel filter has a drain for water that I will periodically drain.  I believe all of the MKIII and up remove water by means of the drain on the filter as well.

[Quantum TD]

A lot of folks remove the separator tank altogether. Since there's a water separator incorporated into the filter, it's somewhat obsolete.

Good luck!

[92EcoDiesel Jetta]

Why did VW use the glow plug LED also for water in fuel indicator? Why didn't they use a dedicated LED? There are 4 un-used LED holes in the Instrument cluster. Is it to save on the cost on one extra LED?

[92EcoDiesel Jetta]

I loosened the 4 water separator mount bolts so I can shake it to stir up the bottom crap to drain it better. I didn't want to open it up fearing breaking the old & brittle plastic fittings. What came out of the drain was much darker after shaking it. I drained about a gallon total before it was clear, however, the LED kept coming back on..
Using the Bently, I traced the water separator sender wires to a 6 terminal plug in the fuse relay panel, unplugged it and put a DVM across the blue/green and brown wire of the sender and it was infinite ohms (very high resistance). I then put the DVM on the capacitance scale and it read 0.3 uf. So I applied 120 vac across the blue/green and brown wires with the intent of zapping the crud that is causing the capacitance. There was a spark and the terminal where I made contact had a weld mark! I put everything back together and the LED is not constanly lit anymore! Glow plug LED working as normal! I have no idea if it will still detect water. I suppose I can put some water in the separator if I was that curious but I'm not. I just didn't want to delete the water separator because it is a great feature to have IMO. Well, that's the story.

[92EcoDiesel Jetta]

My glow plug light is still behaving normal, so the zapping with 120 vac works!

I have a question on the separator. If I unscrew that big round knob off will fuel come pouring out of it? How big an opening is behind it? I was thinking if it exposes a hole of 1 to 2 " diameter, I can pinch off the fuel lines and go in from there to clean the sensor.
Does anyone have a good picture of the water sensor? If not, can you describe it?

[SolarSteve]

If you are going todrain water from it, you hook a tube to the nipple or just get a large coffe can and turn the large handle 3 or 4 turns CCW, then pull down on it and fuel will flow.  IIRC I don't think it comes complete off.  The sensor is just 2 metal pins very close to each other.