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Discussion Starter · #1 ·
I have just been doing full service on 2005 R5 tdi I bought about a year ago,
done everything no problem. I do have an issue with the fuel filter, it has been in the vehicle 5 years going by service history, before I started I was looking on line about it and found a diagram showing the fuel system through the filter. The tank feed according to that should be connected to the VF pipe, on this one it was connected to VM. I connected up as it was and the engine is running fine as it was before the change but this represents a dilemma for me because I like things perfect. Hope this makes sense.
Can anyone tell me if this is OK and even if it is reversed it will run fine, also if it is reversed is there a problem with the return and cooler not going back through the filter, I think that's what happens if it is connected this way around. Much appreciate any advise.
Alan.
 

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No. Its not ok.

When the fuel gets too hot the internal thermostat changes over so the return fuel doesnt mix with incoming fuel. If you installed it in reverse the injectors will be starved of fuel when this temp is breached and can fail either mechanically or electrically.

Bad news is you need a new filter. Reversing it now means you will backflush dirt into the injectors.
 

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Discussion Starter · #3 ·
Thanks for that, I thought that would be the case. Why do you think the filter I replaced has been in the system and I've driven it for a year without a problem. I've only run the engine for a few minutes with the new filter do you think there would be any back flush problem after a few minutes.
Alan.
 

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Thanks for that, I thought that would be the case. Why do you think the filter I replaced has been in the system and I've driven it for a year without a problem. I've only run the engine for a few minutes with the new filter do you think there would be any back flush problem after a few minutes.
Alan.
Filters are cheap compared to injectors.

Some filters doesn't have the thermostat and just loops the fuel through regardless.

Hard to say.

I have a motto. Do it once, do it right!

Get a new filter and fit it correctly.

VF - fuel supply from tank
VM - goes to tandem pump
RT - goes to fuel cooler (heat exchanger)
RF - from the fuel rail (pipe has fuel temp sensor in it)

The filter has a tiny thermostat in it.

I don't know at what temperature it activates but when the fuel is relatively cold the RF infeed mixes with the VF feed to get the fuel up to temperature and eliminate gelling in cold weather. Once the fuel is warm enough the mixing is bypassed and returned straight through the filter bypass back to the tank.













 

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Discussion Starter · #5 ·
Thanks again, it all makes sense. I'm going to get a new filter, what really annoys me is that the filter I replaced and I connected up the new one the same was fitted by a VW dealership going by the service history. It was when I cut into the old one to have a look
I realized it was wrongly installed for the simple reason that the return and the cooler feed did not go back through filtration. Your pics are excellent, I will now cut away the top of mine to see if there is a thermostat.
Thanks again for your knowledge and posting the pictures.
Alan.
 

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All this info looks great. I'm all new to this & wondered what is the start up process after fitting the new filter? Do i need to fill the new one with diesel before fitting? if so through hole VF,VM,RT, or RF? If it doesn't need priming like this how am i best to start it up after this replacement?

Cheers guys
 

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All this info looks great. I'm all new to this & wondered what is the start up process after fitting the new filter? Do i need to fill the new one with diesel before fitting? if so through hole VF,VM,RT, or RF? If it doesn't need priming like this how am i best to start it up after this replacement?

Cheers guys
I prime mine via VCDS.

Otherwise just fill it via the VF port. Crank it till it starts - keep foot flat if it struggles to take. Let the throttle go once it takes.
 
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