I recently came across this post on another site and have also read the post on this site re Ca, Mg and TBN. Being the owner of a Japanese manufactured diesel vehicle, I am interested to hear the opinions of those a lot more knowledgeable than I am.
'The oil sold in Japan typically has calcium based detergents in it at levels of 3000-4500+ppm (parts per million) this is a very detergent oil compared to a lot of oils formulated for American engines (700-2500+ppm) magnesium based detergents, magnesium based detergent is thermally unstable at normal working temps of a Japanese diesel engine that is why it is not used in Japanese OEM oils) as a side benefit extreme levels of calcium have a very strong bearing pacifying affect reducing the bearings susceptibility to chemical attack by its own oil which contributes to the onset of subsurface fatigue failures. Synthetic oil per-se is not a fix (or prevention method) you want oil with low or no magnesium and preferably in excess of 3000+ppm calcium based detergents. The oils that I know of that meet the above requirements are: Caltex Delo CXJ 15w40 (the J is for japanese) mineral oil, Castrol J-Max 15w40 mineral oil, Amsoil Marine oil 15w40 synthetic oil, Amsoil series 3000 5w30 synthetic oil, I know BP in Europe makes some nice high calcium synthetic diesel oils also but I don't know names or product codes'.
'The oil sold in Japan typically has calcium based detergents in it at levels of 3000-4500+ppm (parts per million) this is a very detergent oil compared to a lot of oils formulated for American engines (700-2500+ppm) magnesium based detergents, magnesium based detergent is thermally unstable at normal working temps of a Japanese diesel engine that is why it is not used in Japanese OEM oils) as a side benefit extreme levels of calcium have a very strong bearing pacifying affect reducing the bearings susceptibility to chemical attack by its own oil which contributes to the onset of subsurface fatigue failures. Synthetic oil per-se is not a fix (or prevention method) you want oil with low or no magnesium and preferably in excess of 3000+ppm calcium based detergents. The oils that I know of that meet the above requirements are: Caltex Delo CXJ 15w40 (the J is for japanese) mineral oil, Castrol J-Max 15w40 mineral oil, Amsoil Marine oil 15w40 synthetic oil, Amsoil series 3000 5w30 synthetic oil, I know BP in Europe makes some nice high calcium synthetic diesel oils also but I don't know names or product codes'.