diesel filter on 170 tdi

**toddy2008** · 15-03-2011,09:36 PM

hi al,
can anyone tell me what colour the diesel inside the filter canister should be, i ask this because last weekend i thought i would take a look to see how dirty the fiter looked, the first thing that surprised me was the colour of the fuel, it was a bluey grey colour and the filter was jet black, anyone know if this normal or is it likley that there could be other issues that could cause this (tandem pump ?)
any help much appreciated
thanks again

**towcestervag** · 15-03-2011,10:49 PM

done loads that are jet black
i believe its bleed back from the injectors

**martin1810** · 15-03-2011,10:50 PM

The only way to look at the fuel is take some out in a glass so you can see it properly.
It should look like the stuff from the petrol station pump.

**Crasher** · 15-03-2011,10:52 PM

Tandem pump failure, I see it on about 10% of the ones I change filters on.

**toddy2008** · 15-03-2011,11:18 PM

thanks guys
is there a way of checking the tandem pump, i also get a misfire when accelerating hard (which was why i checked filter in first place) is it likley that the tandam is causing this due to contaminated fuel. thanks again

**Crasher** · 16-03-2011,12:53 AM

If you have cross contamination it is likely that it is the tandem pump, it is virtually impossible to test for this other than by fitting a new pump and seeing if the contamination clears. Bear in mind the fuel tank is probably heavily contaminated.

DSG4ME · 16-03-2011,01:45 AM

It will look blueish, take some and put it in a glass, a few hours later it will be gold with a small black residue in the bottom, if not it looks like you are burning the 505.01 as well.

**a8 tech** · 16-03-2011,08:50 AM

Originally Posted by toddy2008

hi al,
can anyone tell me what colour the diesel inside the filter canister should be, i ask this because last weekend i thought i would take a look to see how dirty the fiter looked, the first thing that surprised me was the colour of the fuel, it was a bluey grey colour and the filter was jet black, anyone know if this normal or is it likley that there could be other issues that could cause this (tandem pump ?)
any help much appreciated
thanks again

Soot content from combustion process returns in the fuel lines and therefore discolours the diesel
Now this is not a problem unless it's excessive which indicates blow pass at the injector seats
Oil will look like soot but if you fill a glass with your fuel sample and leave it for 24 hours then you should see separation of the soot content
Tandem pumps are changed when they are not required and only if excess oil is present should you then check the pump as oil is a fuel and will cause no running issue unless excessive however soot will
I would also replace the filter every 2 years or 20,000 miles

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**toddy2008** · 16-03-2011,09:14 AM

thanks again guys
slightly conflicting thoughts regarding the tandem pump, dont want to spend £200 to find it don't solve the issue, but i will take a sample of fuel and let it settle.
what would be the best place and method of obtaining the sample.
should i syphon it from the tank or from the filter housing?
thanks again
colin