When is water-cooling setup necessary for a turbocharger?
If you look carefully, every turbocharger has different cooling setups by default. Usually you would see turbo with only oil-cooling system on journal bearing turbochargers, but this does not apply to all of the journal bearing turbochargers. There are also journal bearing turbos with both oil and water-cooling system. On the other hand, due to their mechanical design nature, all of the ball bearing system turbos are basically required to cool by both oil and water.
Of course, you may still run these turbos with only oil cooled system, but without appropriate cooling setup, the turbo parts, especially the bearing, would wear out much sooner than you may expect. If you have a turbocharger with only oil-cooling ports, that means only oil-cooling is sufficient for its particular design; however, no matter what the bearing system is, when your turbocharger has both oil and water line ports, it is strongly recommended that you follow the design and set up both oil and water cool. You’ll thank yourself later for going through the extra efforts as in return, you’ll get a more durable turbocharger with longer life.