For a fully illustrated guide to the work carried out in this post, check out my E46 how to guide site - Thermostat (Coolant) - Removal and Replacement
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Since buying the car the mpg has been gradually worsening, dropping from an initial mpg of 38 down to 32.

The car was also not getting up to temperature any where near quick enough. The car should be up to full running temp in around 3 - 4 miles, with the gauge sitting at the 12 o'clock position. The OBC (on board computer) can be manipulated to show the current engine temperature.


Instructions on how to access the hidden OBC functions for an E46 BMW 3 Series:
 
  1. Hold the trip reset stalk, the left of the two stalks in the dash dial cluster, while turning ignition to the on position 
  2. The OBC should now show "Test" in the top left
  3. Press the trip reset stalk to scroll through and select function 19.0, this unlocks all the features
  4. Wait for OBC to show "Off" 
  5. Press the trip reset stalk quickly once 
  6. Then without pausing press the trip reset several times to select function 7, which shows temperature and speed

The ideal temperature range is 88 - 92°C. Mine was reaching 86°C after 12 miles of driving, clearly something was a miss. 

These symptoms suggested that the thermostat was broken. I did a little research and it was suggested that you change the belts whilst you are at it, as you have to strip the engine back to reveal them anyway.

If you're taking the thermostat off, you need to drain the coolant. I was aware that BMW's need specific antifreeze, BMW GS 94000 certified, so I did some research into which coolants were available for the E46 330d. 

I phoned BMW and asked for a price on the antifreeze they supply, for 1.5 litres it came to £9.90. Quite steep when the system takes 10.2 litres of coolant mixture at 50/50 mix.

I'd heard good things about Comma's products, using their product finder it suggested Xstream G48 was approved by BMW and suitable for the E46 330d.

A local motor factors had Comma products in stock, so I picked up 5L of concentrated Xstream G48 for £19.99. You can't just use ordinary tap water when diluting coolant either, the minerals in tap water will corrode the system. Instead, you need to use distilled water, available in most supermarkets and motor factors.

Eurocarparts held stock of both the thermostat and the belts, all for £70. However, if you want genuine BMW parts here's the part numbers:

  • Thermostat - 11512354056
  • Belt - 11287787369
  • AC Belt - 64558593211


First thing to do was get the car jacked up and remove all the engine plastics and the undertrays. 

Then remove the fan shroud and viscous fan. You'll need two 32mm spanners, one with a crank in it to get access to the two nuts securing the fan. They are pretty tricky to get to, as you can see below. 


To remove the fan shroud you have to use a Torx T20 to undo the screw on the top drivers side. There is also a right pain of a plastic clip to remove on the passenger side. Pull the centre pip out and then the main part.



With the fan and shroud removed I started draining the coolant using the radiator drain plug, expansion tank plug and the engine block drain plug. 


I was expecting to drain about 10 litres of coolant out, but in actual fact it was no where near. I actually got around 6 litres out. What came out looked like discoloured water, certainly not blue, further confirming the car's years of neglect. On a positive note though, I was happy to know that the right mix would be going back into the system.


Coolant drained, I started to remove the thermostat. To get at the fixings I had to undo the top of the intake snorkel and move it over a bit. I also had to remove the EGR pipe.


The thermostat really didn't want to come away from the tubing connected to it, I found I had to undo the two bolts securing the plastic piping too.


With the thermostat removed I compared new with old. They differ in design quite a lot, the old one has a considerably more substantial spring. The new one also has a little copper pip that acts as a tiny valve.

Old (left) - New (right)




To avoid any debris getting into the thermostat aperture, I got the replacement fitted before moving onto replace the belts.

Replacing the belts was thankfully very easy on the M57 engine, which was a welcome relief after having a bit of a struggle with the rest of the job.

Belts on, it was time to reassemble the rest of the car. Before putting the fan and shroud back on I took some time to clean them up. Unfortunately I only got pictures of the fan cleaned up.


Everything cleaned up, I filled up the coolant system with distilled water and the Comma Xstream G48 in a 50 / 50 mix. The system took about 7 litres, 1 litre more than came out, so it was obviously a little low before.


The car fired into life and settled down with no overheating nor signs of any leaks. The test drive confirmed the car was now warming up as it should in around 3 miles. It also appeared to have a lot more poke, especially at low revs. I've no idea why but a couple of passengers mentioned it felt quicker without prompt.

All in all, a successful job.

Let me know what you think in the comments below, anybody experienced an even worse mpg drop off than me?