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On the big C-series machines the fan pump is a piston unit rather than a gear pump, which means it can vary its output and can also fail in more ways. This page is deliberately narrow about fitment, because 170-9918 is one of the numbers the trade applies loosely across several tonnage classes.
What Caterpillar calls it
170-9918 is listed as a hydraulic piston pump, with the parts book item name PUMP GP-PISTON. That distinguishes it from the gear-type fan pumps used on the smaller C-series machines such as the 325C, where the supply unit is a ten-tooth gear pump. On a 385C or 390D the fan pump is doing variable output work, and its control is where faults start.
Fitment, stated honestly
Trade parts data and supplier cross-references attach 170-9918 to CAT 374 and 374D, 385C, 390C and 390D, and to the 5090B, running C18 and 3456 engines.
What we cannot confirm: listings that put this pump on a 365C or a 385B. The 365C fan pump in Caterpillar’s own numbering is 247-8968, cross-referenced as 10R-6278, and we list it on its own page. If you have been quoted 170-9918 for a 365C, check the number on the old unit before you accept it. We would rather lose the order than ship a pump that will not bolt up.
The circuit this pump serves
A 385C or 390D in the 80 to 90 tonne band rejects a large amount of heat through its cooling package, and the fan is hydraulically driven with speed controlled from coolant and hydraulic oil temperature. The pump’s displacement is varied in response to that demand. Three failure modes follow from that arrangement:
- Loss of displacement. Internal wear means the pump cannot deliver the flow the fan needs at full command. Fan speed is capped, oil temperature climbs, and the machine derates.
- Control stuck at part stroke. A sticky spool or a failed solenoid holds output low even when the controller asks for full cooling. This is the fault most often misdiagnosed as a bad fan motor.
- Cavitation from the supply side. A restricted suction line or a low oil level makes the pump noise and slowly destroys it. If the old pump was noisy before it failed, check the suction path before blaming the unit.
Test in that order. Our hydraulic fan pump diagnosis guide covers flow and delivery pressure measurement, and the regulator article covers the control signal. The mating motors in this class are 225-4613 for the 365C and 247-8978 for the 385C and 390D, and they are not interchangeable.
Fitting notes
Compare shaft, pilot, bolt pattern and port orientation against the removed unit before cleanup begins. Prime the casing with clean oil before cranking. Fit a new return filter element and clear the suction strainer. Route the case drain directly to tank with no restriction, since back-pressure in the casing is what finishes shaft seals. Confirm the control connector is seated, then prove full fan speed under thermal load and log both temperatures.
Cleanliness target for axial piston units in mobile service is around ISO 4406 18/16/13 on Bosch Rexroth guidance. If the machine has already lost a pump, inspect the drive train before fitting: drive gear inspection ve transfer case failure diagnosis cover what to look for.
Terms
Minimum order one piece. New aftermarket units carry a three to six month warranty as stated on your proforma invoice. Bench tested, photographed against your order before the wooden case closes, delivery 5 to 8 working days from payment subject to stock, by sea, air or express courier. Related pages: 247-8968 fan pump ve 225-4613 fan motor. The full range sits under Caterpillar hydraulic fan motor.
