Beschrijving
Motor graders are the clearest case for a variable-speed hydraulic fan in the whole Cat range, and Caterpillar says so in their own specification. That makes this pump an interesting part: it is the component that decides whether the machine gets the cooling it asks for, and it is the reason a grader can hold a road surface at low speed without cooking itself.
What Caterpillar states
250-8337 is listed as a Hydraulic Fan Piston Pump. Component data identifies the underlying unit as a Bosch Rexroth variable displacement axial piston pump, catalogue reference R986110089, and the remanufactured Cat reference is 20R-0109. Applicability covers the M-series graders 120M, 12M, 140M, 14M and 160M.
The fan this pump controls, in Cat’s own numbers
Caterpillar’s 140M specification is unusually specific about the cooling system, which is helpful when you are trying to judge whether a heat complaint is a pump fault or something else:
| Item | Caterpillar figure, M-series grader |
|---|---|
| Fan control type | Hydraulic demand fan, automatically adjusts speed to cooling requirements |
| Stated benefit | More power to the ground and improved fuel efficiency |
| Fan speed, minimum | 600 rpm |
| Fan speed, maximum standard | 1,450 rpm |
| Fan speed, maximum high-ambient | 1,650 rpm |
| High-ambient rating | 122 F |
| 140M engine and power | Cat C7 ACERT, base 183 hp net in first gear, VHP Plus range 136 to 174 kW at 2,000 rpm |
| 120M engine and power | Cat C6.6 ACERT, base 138 hp (103 kW) net, VHP Plus 103 to 136 kW |
Read the minimum figure first. A fan idling at 600 rpm on a grader moving at walking pace with the blade loaded is a machine whose pump is doing exactly what it should. When that same machine starts running hot, the first question is whether the pump is being commanded to rise, not whether the pump is worn.
Diagnosis order for a grader that runs hot
- Clean the cores. Graders work in the dust they are grading, and a roading crew will rarely have time to do it properly.
- Watch the fan respond. If speed does not climb as oil and coolant temperature rise, the fault is in the command or the pump control, and the difference matters when you order.
- Check the oil level, the return filter and the suction strainer. A starved variable pump makes noise before it fails.
- Measure delivery pressure and flow. Our hydraulic fan pump diagnosis guide covers the test, and the regulator article covers the control signal.
- Then judge the pump itself, and change the filter element as part of the job regardless.
A note on listings that call this a gear pump
Some supplier pages describe 250-8337 as a gear pump. Caterpillar’s own title says piston, and the Bosch Rexroth platform behind it is a variable displacement axial piston unit. The distinction is not pedantic: a gear pump cannot meter output the way this circuit expects, and a substitution based on bolt pattern alone will leave the grader running its fan at a fixed speed, which on a machine with a demand fan is a cooling and fuel problem at the same time.
Fitting
Match shaft spline, pilot, flange, port positions and control orientation against the removed pump. Prime the casing with clean oil before cranking. Keep the case drain unrestricted to tank, within the published 0.1 MPa normal and 0.4 MPa peak limits for casing drain pressure. Target cleanliness around ISO 4406 18/16/13. Prove that the fan accelerates under thermal load and that it settles back to the low speed at cold start, which is the signature of a circuit working correctly.
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. The rest of the CAT cooling drive range is under Caterpillar hydraulic fan motor, and the diagnosis sequence for the fan motor side is in our fan motor guide.
