35d worsening gas mileage - solved- thermostat/fan/EGR cooler - DIY with pics

[Stockx5]

Mine would not rise above 68c
Few distinctions that might be of interest:

1. Instead of the OEM I bought Beck/Arnley 143-0904 Thermostat Housing. from ebay member 3wardist for $44.67. housing is identical except for the serials and bmw logo. the internals are not the same. you can see oem on the left here and the Arnley on the right.
mainly the Arnley has a bigger copper core, and the springs have a lot less travel than OEM. Which one is a better part not sure but I will be happy to post when it fails.




2. 2 of my t-45 torx nuts on the egr cooler had already been replaced by regular nuts presumably by the dealer. After dropping the non magnetic flange bolts 3 times and finally losing one of them I went to home depot and bought the identical length/thread bolts. this is the size in case someone is wondering.


3.I noticed the EGR valve which had been replaced 18k miles ago by dealer with the updated part was completely caked up in soot. So was the throttle valve and so was the intake manifold.




This is what came of the EGR valve alone


Id be interested to see others egr valves to see if this is normal caking up procedure for diesel engines or if this was caused by the failed thermostat or if this is just what egr cooler does to our egines the car has 103k miles.

Either way it seems a glow plug/injector/EGRvalve/catalitic converter/dpf filter/engine would not last long if this contamination was being constantly pumped in.

[daytonatrbo]

Originally Posted by Stockx5

Mine would not rise above 68c
Few distinctions that might be of interest:

1. Instead of the OEM I bought Beck/Arnley 143-0904 Thermostat Housing. from ebay member 3wardist for $44.67. housing is identical except for the serials and bmw logo. the internals are not the same. you can see oem on the left here and the Arnley on the right.
mainly the Arnley has a bigger copper core, and the springs have a lot less travel than OEM. Which one is a better part not sure but I will be happy to post when it fails.




2. 2 of my t-45 torx nuts on the egr cooler had already been replaced by regular nuts presumably by the dealer. After dropping the non magnetic flange bolts 3 times and finally losing one of them I went to home depot and bought the identical length/thread bolts. this is the size in case someone is wondering.


3.I noticed the EGR valve which had been replaced 18k miles ago by dealer with the updated part was completely caked up in soot. So was the throttle valve and so was the intake manifold.


This is what came of the EGR valve alone

Id be interested to see others egr valves to see if this is normal caking up procedure for diesel engines or if this was caused by the failed thermostat or if this is just what egr cooler does to our egines the car has 103k miles.

Either way it seems a glow plug/injector/EGRvalve/catalitic converter/dpf filter/engine would not last long if this contamination was being constantly pumped in.

One of my EGR cooler flange bolts had been traded for a standard steel bolt. I found the original torx bolt laying in the plastic belly pan. I didn't find it until the job was done. So I have it in my tool box for the next time I have it all apart.


Your soot/cbu looks severe for only 18k miles. But that may be attributable to the cold running engine. The engine is made to run rich when not at temperature, and that makes a lot more soot.

If not for the dpf and catalysts, we would likely have a visual warning that there was an issue because the exhaust would be come darker.


I still can't believe how many of these diesels have failed thermostats and the dealer techs and private specialists still seem unaware of the issue or to check for it.