mini_me

In my 'quest' te find the source of the higher-ish fuel consumption I checked my engine temp via the OBD hidden menu some time ago. It turned out the with an ambient temperature of about 5C the engine temperature would not exceed 65-70C.

The symptoms when driving are as follows; engine quickly reached temperature between 60-70C. When idling or in slow moving traffic the temp would go up to about 70C, when riding it would drop to about 64C. FYI all this time the shutters behind the front grill are closed.

You will hear a lot of people, including BMW mechanics (!!) say that this is normal behaviour for modern efficient DI diesels. In my book and with my engineering knowledge this is bullshit! I must say with also the BMW mechanics saying it is normal they had me in doubt but I am glad I stuck to my opinion that this isn't a correct temp even with lower ambient temps. Imagine what would happen when you would drive your car at -20C ambient temps, the engine wouldn't reacht 40C operating temp.

Even a very efficient engine should reach operating temp with all thermostats closed. After all with all thermostats closed the engine hardly gets any cooling since it is only using the short cooling circuit.

I was able to convince my dealer that low ambient temps should not prevent an angine (even a very efficient one) from reaching normal operating temp of about 90C. In an attempt to solve this they replaced the normal thermostat, which also in my belief, was causing all this. To my and their surprise this didn't solve the problem. As a double check they also took another 525D car and drove it around to check the temp on that car. (a good gesture I think!) This 2nd car also only reached 65C temp. So my case was closed as being strange but normal (since they double checked with other 525D).

After doing some searching on various forums I noticed that it could very well be the 2nd smaller EGR thermostat that was causing the problems. In my book this made sense since the fact that the engines temp dropped when driving to me indicated that somehow the radiator was involved in cooling the coolant.

A defective EGR thermostat (defective as in; opened all the time) will act as a bypass to the main thermostat. This 'bypass' is small, but still big enough tho drop the engine temps down to about 65C.
I decided to buy a new EGR thermostat and O-ring (total cast about EUR 31) and replaced it. Simple job which takes about 1/2 hour with good preperation.

The result; Engine quickly up to normal operating temp. of about 90C even with low ambient temps and my faith in BMW engineering restored.

I have added a simplified drawing of the cooling system including the EGT thermostat.

Anzafin

Very useful info and great reasoning!
Thank you for publishing your finds and congrats on the solved problem !

Phantom Mark

Now all that remains is to see if your fuel economy returns to a sensible value....?

mini_me

True ;-)

Palmo

Great result - it sometimes pays to be persistent!

Let us know how the fuel economy goes!

eddie12

Does the coolant have to be partially drained and then topped up again to change the EGR stat?

mini_me

No, taking off the hose to the EGR you will have some coolant leaking but it's only minor. It is so little that in my case topping up wasn't needed.
At the top of the EGR thermostat there is a bleed screw so bleeding the system is a breeze.

eddie12

Thanks for the info 'mini me'.

E61530DAT

mini_me.... sendt you a PM. Thank you for your post. I have the same problem with my E61 530DAT with operating temperature not higher than 62 - 67 C. Would very much like a work description on how replace this EGR thermostat.

Edit: Do you have the thermostat part number?

schulrog

did you go to your SA and smack him across the face with the old thermostat? lol