Golf fuel filter.

[Julian]

Last winter I chickened out of running the Golf on Bio in the depths of the winter (such as it was), but think I'll give it a try this year.

Biggest fear, after swabbing out the Disco tank several times in the past, is "HPME".  I now have an outside storage tank so the fuel should be reasonably well conditioned prior to use and I'll just keep around ¼ tank max in the car so if they form, there won't be that many.

Anyway, I've done some reading and the fuel filter, besides the normal flow and return has two additional pipes attached.  These apparently are the spill form the pump and possibly the injectors.  It's a PD engine so the injectors are buried within the depths of the engine and never see the light of day, so I'm not sure if there are any spill lines from them ... possibly not.

The spill line enters the filter via a little valve.  It seem this is a diverter valve which switches between 15°C and 31°C and either directs the fuel into the filter or back to the tank.  The 31°C seems a health temperature to eliminate "HMPEs" but the valve has a massive differential and although 15°C is way better than a low winter ambient, I'd like the filter to be running at a higher temperature.

My current thoughts are to remove the valve and make an adapter to divert all the return fuel, regardless of temperature, into the filter and block off the now redundant fuel line back to the tank.  I'd be inclined to return it back to standard for summer use.

So, VW experts ... have I had yet another really stupid idea?

Does anyone know the sort of flow rate in the spill line (physically is the same size as the supply line).

Does anyone know the sorts of temperature the return line gets up to (I know it's largely effected by ambient temperature)?

[julianf]

I can not answer any of your questions exactly, however, if youre returning all the fuel, all of the time, it will be hard to bleed air.

I dont know how it bleeds when its cold anyhow (as then the valve will return the fuel) but, with just one pipe up from the tank, the only place for the air to go is through the injectors.

[Julian]

I can not answer any of your questions exactly, however, if youre returning all the fuel, all of the time, it will be hard to bleed air.

I dont know how it bleeds when its cold anyhow (as then the valve will return the fuel) but, with just one pipe up from the tank, the only place for the air to go is through the injectors.

Good point, I could incorporate a bleed screw in the adapter I make.

[julianf]

i know that space is tight, but could you change the whole filter head?

i suspect that landrover ones would be no good, as (if its a mk4) you have to lift the filter up, past where the head would be, but, if youre making up a plug for the original, there might be better options alltogehter?

[Julian]

I've got a Disco filter housing and many spare filters, one of those little square VW oil cooler heat exchangers and have even started to make adapters to graft the two together with the ultimate view of fitting it, but as with so many things I've not got round to finishing it!

The suggestion above will be much quicker, a little bit of turning and soldering plus an "O" ring.   I'm temped to try printing one, but I can imagine the ramifications lasting weeks if the car breaks down.  I'm already having great difficulty in persuading her she'll make the round trip of 10 miles to work on a ¼ of a tank!

That's the trouble, you spoil them with free fuel and they just want more ... shame that's not the case in other areas!

[1958steveflying]

Hi Julian.... do not do that mate, because of where the fuel lines are in the head to the injectors the fuel temperature gets very high, if you look under the drivers floor you will see a plate covering a fuel cooler to further cool it on its way back to the tank, also the return flow on this system is higher than a normal spill injector. To be honest I think you will not need to worry about winter use with bio and the pd given your bio storage plans.

[1958steveflying]

Oh and the fuel line by the dual pump on the end of the cam has a temperature sensor in it which plays with all sorts of ecu settings based on the temp of the fuel.

[Julian]

Very helpful info, thank you.  I've vague recollections of the plate you describe under the car from one of the few excursions underneath.

So a better plan would be to keep the existing set up but to try and reduce the differential between cut in and out of the diverter valve to try and keep a constant 31+°C in the filter.

I wonder if the valves have different specs depending on local climate ie higher temps in Scandinavia.

[1958steveflying]

TBH I have never taken a close look at this valve, all I know is the filters on them run hot pretty much all the time, especially where they are fitted as well. We had a Pd golf and it always started and ran in the winter without issues when my Fiat and Vw camper would not even start until the weather warmed due to the bio.

[Julian]

TBH I have never taken a close look at this valve, all I know is the filters on them run hot pretty much all the time, especially where they are fitted as well. We had a Pd golf and it always started and ran in the winter without issues when my Fiat and Vw camper would not even start until the weather warmed due to the bio.

Heartening news, thanks Steve.

I might measure some temperatures of the various connections on start up and at running temperature just to put my mind at rest!