Im confused! You all keep talking about him having oil in the coolant. The thread title says "Water in the oil"......Think about it: If you had oil in the water, you would possibly have an oil cooler, intake, or crack in an oil galley close to a water galley. Oil has more pressure that is capable of putting pressure into a cooling system. Your cooling system has less pressure than the oil system so.......you wont be as likely to have oil in your water. If you do, those are possible causes. Water in oil....as the thread says, more than likely is a bad head gasket (more than likely), possible intake gasket but not too likely, cracked block that the crack expands when block is hot. An engine with 163k miles is much more likely to have a blown head gasket or cracked head than any other issue. Does the oil look "milky", show streaks of oil/water mix on the dipstick, have a smell of antifreeze in the exhaust? I have seen large engines run with no smoke in the exhaust and have bad head gaskets. Just be careful with loosing water. Could sit on top of a piston and either lock the engine up or possibly do worse.