Just wanted to post this to hopefully help others out. I noticed that my coolant temp (on cluster) was just above C (first line) constantly, even if I was running for an hour. For some reason I didn't think this was right. After further investigation I found a page explaining the importance for a diesel to maintain a decent temp in the engine, especially ours seeings as the injectors use the high pressure oil (and electric) to fire them. If this was the case then "cold" oil wouldn't make the injectors fire as efficiently, makes sense right!?.
I came to the conclusion that I was going to spend the $18 for a new Tstat. When I removed the one installed, I found that it was made in Germany and had a few rubber seals on it that were in very poor condition. Swapping it out with a US brand for no more than an hours work at very little cost.
Now my coolant temp gauge is constantly around the "R" of the "normal" in the range. I can also safely say that my engine hasn't ever felt this good since I bought the thing! I feel as if I am getting more power and more mpg.
I hope this thread helps others out, I'm not a mechanic by any means but with a little help and looking on other sites/pages it brought me to these conclusions.
Here is my other post.
Coolant gauge indication
My coolant gauge before.
Coolant gauge now.
Sorry for sideways photo! LOL