The key to the question has to do with the somewhat strange cooling system in these engines. I'm sure someone can explain it better then me, but as far as I understand, the temp sensor is located at the return from the rediators (I think you can fined the full explanation in earlier posts in this tread). There are parts of the engine (around cylinder 6 if I remember correctly) that are much hotter than what you see on the gage. So even thogh the gage show same readings, the engine itself runs much cooler.
That's more or less what I understood before I got main
