Hi everyone. For once this isn't a topic about a problem with a Freelander 2! I know there are some very knowledgeable people that are very clued up about the cars we drive on this forum. I quite like knowing the inner workings/the geeky bits of Freelander 2's and hope you don't mind me picking your brains.

I know that the Freelander 2 has a system where it warms up the diesel to stop it waxing(?) which, from what I've read on various posts on here, uses the fuel filter and high pressure pump. That's about the extent of my knowledge on this.

So what I'd like to know is, what is exactly involved? Let me set the scene. It's a cold, frosty winters day in the UK and it's 0 degrees and the cars covered in frost. I jump in, start the car and it fires into life.

- Is there a set temperature outside that this diesel warming happens or does the outside temperature have no bearings on it? Will it do it on a summer's day until the fuel gets to a certain temperature? Anyone know what the target temperature that it keeps the fuel at?

- I've heard that a certain amount of fuel gets returned from the high pressure fuel pump. How does it know how much to return and when to stop returning it?

- Is it just to warm up the filter which in turn warms up the fuel? Or is it's end game to keep returning warm fuel until the fuel in the tank is warm?

- Is/Was this system unique to the Freelander 2 or was it a system that was widely used in diesels?

If someone can explain what the journey is from when it's stone cold in the tank all the way to being nice and toasty, that would be much appreciated.

Not to forget that diesel sold in winter in cold climates has additional additives.

Down under the lowest temperature I have had is -4°C & not even skiing, but with petrol there are no issues. Procrastination, mankind's greatest labour saving device!

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Glow plugs
https://www.freel2.com/gallery/albums/userpics/11383/glows.pdf
Fuel filter
http://www.freel2.com/forum/post96179.html#96179
Sorry the post is in Romanian but the pertinent image is annotated in English.

Thanks for the post BossBob. Here's where I'm at so far with trying to figure out how the Freelander 2 warms up the diesel when it's cold.

1. The stone cold fuel gets pulled from the fuel tank via the fuel pump, into the fuel lines to the front of the car.

2. The fuel lines connect to the fuel filter where the cold fuel is passed through the filter. The temperature sensor somewhere within the fuel filter detects the temperature of the fuel and reports it to the ECU(?).

3. The ECU(?) notices that the fuel is cold and below the temperature it requires. It then tells the fuel filter to open a passage on the return line section of the fuel filter to allow returned fuel to enter into?

4. The fuel, while still cold is sent to the high pressure fuel pump and then onto the injectors to be combusted.

5. The pressure(?) of the high pressure fuel pump warms the fuel(?). An unknown percentage of this warmed fuel is sent down the high pressure fuel pump leak off pipe which is connected to the return side of the fuel filter. (Does the ECU tell the fuel pump to send fuel down the return line or is it always doing this?)

6. That warm fuel from the leak off pipe enters the return line of the fuel filter and because the ECU(?) knows that the fuel is cold, the warm fuel drops into the fuel filter, thus warming it and the fuel running through it.

7. This continues until the fuel temperature sensor in the fuel filter detects that the fuel is warm enough and closes the port within the fuel filter to stop the returned fuel from constantly warming it up.

8. Instead of warming the fuel up within the fuel filter. It now bypasses the fuel filter and has a direct trip back to the tank.

How close am I? I feel like I could be along the right lines with a few errors here and there?

My Diesel filter doesn't have any sensors connected to it, I don't think many in the UK do.

Typical cold start is press the start button and there will be a variable time delay depending on how cold it is, whilst the Glow Plugs warm up the diesel, before the engine tries to start. You may see the glow plug symbol appear on the dash. 
Hung like Einstein, smart as a horse.

You can see at about 2:50 in this video ( https://youtu.be/fuAY1_hFuPQ?si=zB25-hIfW2ubfdBK) that we disconnected the fuel temperature sensor from the filter.

I know about the glowplug/engine/cranking side of it. Just trying to get to the bottom of the fuel warming process.

The fuel filter bypass valve is entirely mechanical and recirculates 95% of fuel when returning fuel is below 10C.

Its all in the free JLR workshop manual - download it and read at your leisure - go to home and follow the link

eg page 1589


 Jules

What Jules says. The thermal system in the fuel filter is self contained. That is why it is so important to use an authentic filter.

Hi, Greetings from Norway!

Have no idea of the fuel return/warmer system. In general, it should be OK as long as you fill diesel in the same area as it is used. There will be additives added to the diesel from the supplier when sold below a certain temperature. Think it can be thinned with some paraffin IIRC if "winter diesel" is not available. We are talking below -5C. Except for that, make sure the glow plugs are working and the battery and filter is in good shape. Mine fires without problem in -15C, but have a habit of giving it a "double glow" before I fire it up at that temperatures.

The FL2 is built and tested for -35C, so it should be no problem

Dean1234 wrote:

You can see at about 2:50 in this video ( https://youtu.be/fuAY1_hFuPQ?si=zB25-hIfW2ubfdBK) that we disconnected the fuel temperature sensor from the filter.

I know about the glowplug/engine/cranking side of it. Just trying to get to the bottom of the fuel warming process.

Ah, I was thinking about the bottom of the filter, there are some FL2s that have an electrical component that connects into the bottom of the filter. 
Hung like Einstein, smart as a horse.

Its for a water sensor though not fitted on most FL2s 2013 FL2 XS.
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That puzzled me for a while as my 2014 even has the wire and connector for that in its loom - but the filter have no sensor just a dummy connection - a rollover from the Evoque loom at the end of the FL's run. Jules

MRRover75 wrote:

Hi, Greetings from Norway!

Have no idea of the fuel return/warmer system. In general, it should be OK as long as you fill diesel in the same area as it is used. There will be additives added to the diesel from the supplier when sold below a certain temperature. Think it can be thinned with some paraffin IIRC if "winter diesel" is not available. We are talking below -5C. Except for that, make sure the glow plugs are working and the battery and filter is in good shape. Mine fires without problem in -15C, but have a habit of giving it a "double glow" before I fire it up at that temperatures.

The FL2 is built and tested for -35C, so it should be no problem

As above Back last winter we had a few weeks (don't laugh MRRover75) of -12 +/- degC and the Freelander started with no problem at all. Double glow plug and keeping the battery in tip top condition is critical. When it is due to get cold like this I tend to stick the battery conditioner (CTEK) on overnight to keep things warm and charged. Never fails to start in the morning.

Just to round up this thread and in case anyone else is interested in how the Freelander 2 warms up the diesel on cold days in a very basic form. I first started off by opening up an old diesel filter we had to see what was inside and how it worked:

https://youtu.be/r4EXcB2a44E

You can see at 7:14 in the video the return line and the thermostat inside.

I talk about it in a more fuller sense with a basic animation in this video at 0:52:

https://youtu.be/e4D623-88-Q

Click image to enlarge