TWR0018 is a downflow radiator for the Western Star 4900.
The core measures 31" high by 35" wide, 3.0625" deep. It has a 2.5" inlet at the right and a 4" outlet at the dual. There is no integral oil cooler and no filler neck.
It replaces 2 OEM and aftermarket numbers, among them 800139, 800139BT. Searching any one of them will find this part.
On radiators the inlet and outlet positions, and whether the unit carries an oil cooler, decide interchangeability more often than core size does. Two radiators with identical cores are frequently not interchangeable.
