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How To: SDI/TDI Fuel Filter Change


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Changed the fuel filter the other day on my SDI. It's a slightly different process on a TDI but I'll tell you from memory how to do it for both. This should only take you about 15-20 minutes to do but is a nice bit of preventative maintenance. You need a new fuel filter when your car becomes harder to start and experiences dead spots across the rev range. On a TDI, it's more important as it can strain and cause excessive wear to the fuel pump. As the SDI doesn't have a fuel pump, everything is driven by the injector pump so it's fairly hard to cause any damage but it's always worth changing them anyway for good measure.

Just as a pre-warning, you need to work out which fuel filter to buy. Older SDI models come with a thermostatic valve that takes an R clip, newer SDI's and TDI's come with a thermostatic valve identical to the MK4 Golf which takes a mickey mouse clip.

If yours has an R-Clip then you need a part equivalent to: 6N0127401R

If yours has a mickey mouse clip, you need a part equivalent to: 6N0127401H

O-Rings should be supplied, if not are 503440740 from EuroCarParts and cost just £1.32 a pack. If you've been supplied with two black O-Rings I suggest buying a pack from ECP anyway because there should be one blue and one black. Two black can damage the thermostatic valve.

Fuel filters are not interchangeable (the thermostatic valves are different sizes) and because the supply and return hoses are the opposite way round, converting from one to the other is difficult, as you'll need to swap the fuel pipes over going into the injector pump. It's much easier to simply buy the correct filter for your vehicle + O-Rings.

Also before you begin, don't forget to grab yourself a jerry can with some diesel and a funnel, especially if you have an SDI. Pre-filling the fuel filter is quite important. Also don't forget to put some actual fuel in your tank!!!

Mine has a mickey mouse clip so that's what I'll be describing in this thread.

1. Untighten the screw that secures the fuel filter inside the circular holder.

2. Using a set of ordinary pliers, move the hose clamps on the fuel supply line so they're nice and far back.

3. Pull the fuel supply line hoses off the filter ports. It may take some effort, so be prepared to use those pliers you used earlier. Also expect a little bit of leakage. This is normal though.

4. Now remove the mickey mouse clip by pulling away from the filter. It shouldn't require too much effort but it'll need a little tug. Fingers are fine.

lDPfJEF.jpg

In the photo above, I have also moved the return line hose clamps back as marked in red. This really isn't necessary unless your thermostatic valve is visibly damaged.

5. Now lift the thermostatic valve out of the bleed hole. This will be a tight fit as the vacuum pulls the thermostatic valve down.

6. You can safely lift out the old filter and put in the new one.

Step 7 and Step 8 are interchangeable.

7. Right, pre-filling. Personally, I don't recommend recycling the diesel from the old fuel filter. If you pour it into a tub, you'll see that a lot of sediment and crap will come out. Fresh is almost certainly better. Using a funnel, pre-fill from your jerry can using the bleed hole at the top. Go slow, as it takes a while for the diesel to seep into the filter element and rushing will certainly either spill or overfill.

8. Once you've done that you need to decide whether to change your O-Rings on the thermostatic valve. Personally, I change them every time. At £1.32 a pair as posted above, it's not worth the hassle. However if you're a tight bugger, you can coat them in lithium grease and they'll probably work fine. Lithium grease has a fairly good track record for this job on VW Vortex and other VW forums so it's up to you really.

If you decide to be a good boy (or girl) and change them, then turn the valve over (if you've moved the hose clips it'll spin okay, if not, you can still turn it over quite a lot) and remove them using a flathead screw driver. Easiest way is to break them. The blue one is easier to remove as it's softer, the black one is a bit of a bugger.

You need to put the black one on first and then roll the blue one over. You'll only get it wrong once. Once they're on, they're on, you'll damage them if you try and correct your mistake, so get it right or buy a new pair!!

qGGyqIp.png

9. Once you're done, push the thermostatic valve back in. It'll be a tight squeeze again but you'll know once it's sealed. Put the mickey mouse clip back in and then re-attach the fuel supply hoses. I recommend moving all the hose clips back to where they were as it reduces the chance of air getting sucked in, however a lot of people on other VW forums wait until they've confirmed it's all working. I say why risk it?

Regarding the securing screw, as far as I'm concerned, tightening it up is unnecessary. As I'm sure you're now aware, the fuel filter is a tight enough fit as it is, and the screw is an absolute lovely person to undo and tighten, so I just leave it untightened. The fuel filter isn't going anywhere though I assure you, but up to you what you decide.

10. Starting your car... right, this differs for an SDI and a TDI, because a TDI has a proper dedicated fuel pump, whereas the SDI has only an injection pump. This is why pre-filling the fuel filter is absolutely vital on an SDI. It is not as important on a TDI and I'll explain why below:

SDI - Start your vehicle and immediately lift your revs to roughly 1300-1500. I suggest holding it there for at least a minute, if not more. Holding the revs will purge any air in the lines. If you let your revs drop to idle too soon, the car may cut out as not all air is purged from the injector pump. This will be evidenced by the 'beer froth' effect in the clear fuel lines as air rushes back up to the fuel filter from the injector pump. Don't be too worried if your revs flutter, this is normal. Once the air is purged, you'll be able to hold it at a constant revs without any fluttering. Allow the revs to slowly drop to idle and then leave it for another 20-30 seconds. If it idles okay without stalling, job done. If it stalls, then you've got a problem as either air is being sucked in, or not all air has been purged. Either way, you'll probably need to bleed using the bleed nipple under the engine cover.

TDI - Lucky buggers do have an actual fuel pump, so you don't have to technically pre-fill your filter, as the fuel pump can do it. However I recommend pre-filling some anyway. Regardless, even if you do decide to pre-fill, it might be worth cycling your ignition without starting the car 4 or 5 times just to shift any air that might be in the lines. The fuel pump should do this no problem. Start your car and perhaps hold the revs for 30 seconds, but really on a TDI this shouldn't be necessary. It should start first time and without a problem, just don't forget to cycle the ignition a few times!! ;):)

Edited by Skezza
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  • 5 years later...
On 3/13/2020 at 8:24 AM, C3peteo said:

How are you going to do the diesel purge?

I used this method: Not forgetting to change your fuel filter at the same time. Did I notice a difference; yes I did 🙂 

 

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  • 3 years later...

Hi, another big thumbs-up for posting this. I changed the fuel filter in my TDI today and could find absolutely no reference to the order of the O-ring colours anywhere on the internet except here. Thank you.

Nothing available from filter manufacturer (Mann filters), nothing from vendor (Euro Car Parts). The best the latter could offer was to copy what's already there. Imagine my delight when I removed my filter and found two identical o-rings!

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