E46 320d EGR thermostat replacement

[gjm 3193]

The 320d had seen a slight drop off in economy, and also a marked increase in time taken to get to operating temperature.

These engines, like the M47TUD20 in the 320d, have two thermostats - one is the more-or-less conventional item in the cooling system, and the second is associated with the EGR (exhaust gas recirculation) system.

The EGR thermostat appears to be the one to most commonly give up, is generally the simplest to replace, and is also the cheapest. As good a place to start as any, then.

A little internet searching turned up the video below. 3 minutes, huh? Can't be too bad!

So it didn't take 3 minutes. The video doesn't show R&R of the plastic engine covers for a start, but they have to be taken off for just about anything.

Some differences (from the video procedure) experienced:

• The screw holding the vacuum pipe in place on my car has a torx head
• The hose on the right hand side of the EGR thermostat is held by a fancy clip, not a jubilee-type one.
• There's an engine lifting bracket behind the EGR thermostat
• The hose connecting the vacuum pipe leads into a solid pipe, which will not lift out of the way as shown

I followed the same process with the necessary changes for my car. When it came to removing the two 10mm bolts to release the thermostat, I had to use a 1/4" drive 10mm socket, a UJ coupling and a short extension. This is awkward but not impossible to get into position - the biggest challenge is not rounding the head of the bolt when removing or refitting.

Something I don't think the video shows is replacement of the yellow o-ring that fits on to the thermostat. I smeared the tiniest amount of Hylomar around the shoulder this sits on to before refitting.

OK, so it's not a 3-minute job. End-to-end, including finding the right tools, it took perhaps 30 minutes. As with so many tasks of this nature, it'd probably be quicker if doing it again.

Result? Well, the engine comes up to temperature much faster (again). Can't yet comment on the economy, and maybe it was psychological, but I felt the car was generally running better post-swap than before. Nothing tangible, nothing serious, just seemed a little smoother. I may have imagined it.

I bought the parts from Coombes Johnson in Hamilton and cost was about $100. You can find them cheaper online, but I was in a bit of a hurry to get it sorted. Ordered Thursday, collected Friday, fitted Sunday.

Edited to correct the engine designation.

Edited September 21, 2014 by gjm

[coop 261]

Parts for these aren't badly priced eh...

What kind of fuel mileage are you getting out of it, highway and city?

Have you addressed the swirl flap issue?

I did mine the day I bought it, although I used self tappers and loctite silicon/silastic, am not sure if they've sealed from any boost leaks completely, so will order the proper machined blanking plugs as well as this thermostat off ebay when I get around to it.

Also when I had the intake manifold off she was caked in carbon. Didnt have enough time to clean it properly, might just buy a complete new manifold to save time. Will see if this all this improves mpg.

[gjm 3193]

Ours is a UK import car.

Mileage varies, from 600+ miles to a tank, down to 500++. That's based on 60 or so litres - I figured 10 miles per litre can't be bad. (Around 16km per litre, 6-ish litres per 100km, a little better on a long run.)

I have the biggest pile of history with the car you can imagine. This includes some work done in the UK, the import papers, and lots more. There's documentation describing an issue with swirl flaps and removal, but no mention of blocking or plugging. I've not pulled the manifold to check - it's on the cards.

If you're keen, a hybrid turbo, decat exhaust and a remap/ecu swap will see upwards of 190bhp.

See also my thread - Life with a high mileage car.