Your past oil changing procedure does nothing for engine longevity, no matter what the experience was. Your attention to the maintenance schedule was probably the defining factor of engine longevity.
I'd suggest to use what the Mfg lists as compatible engine oil. My experience is that shortening maintenance intervals during the first 50K miles of ownership can add to vehicle longevity. Diesel engine motor oil contains a lot of surfactant. This is to lift contaminants from wear surfaces and will expose itself by oil that turns black, quickly. Nothing wrong with that.
If you really want clean oil, look into an after market, auxiliary oil filter that will help with capturing contaminants.