Toyota Repair: ERRATIC IDLE, piston ring, belt transmission

Question
I HAVE A VERY CLEAN 1994 BASE MODEL P/U W/AFTERMARKET A.C.APPROX.140000 MILES.NEW TIME BELT TRANSMISSION FACTORY REBUILD.REGULAR MAINTENANCE.APPEARS TO BE WATER IN MY ENGINE.MOTOR OIL LOOKS YELLOWISH TO WHITE AND FOAMY.RUNS GREAT WHEN COLD THEN OVERHEATS WITHIN 15MIN.TO 5 MILES.COULD I HAVE A SIMPLE GASKET PROBLEM OR IS THIS A MAJOR EXPENSE? ALL POSSIBLE SOLUTIONS WOULD BE APPRECIATED AND INVESTIGATED.THANKS

Answer
These engines are known to have headgasket problems so I suspect that is the case. The first step is to remove the heads for inspection, it may also be a good idea to have the cylinder heads checked for any cracks and if there are none, have the heads resurfaced and do a complete valve job.
At the time the heads are removed inspect each cylinder wall for excessive scoring which would indicate a piston ring problem, rotate the engine and make sure each piston moves all the way to the top, there have been cases where too much water entered a cylinder and caused hydraulic lock up, this can bend a connecting rod.
So yes, depending on what is the required repair it can turn into a major expense.