Home CAT Pressure Washer Pump Guide
Pump-manufacturer compatibility
CAT Pressure Washer Pump Guide
CAT publishes unusually useful replacement guidance for gas-engine pressure washers. Use shaft type, diameter, nominal RPM, engine torque, flow, pressure and port configuration together before declaring a CAT pump compatible.
CAT replacement matching starts at the engine shaft
Confirm a horizontal, straight keyed shaft, exact diameter and engine torque at operating RPM before comparing CAT direct-drive pumps.
The Pump Finder includes an initial CAT 4DNX record, but final fit still requires mounting and plumbing verification.
Last technical review for this page: August 28, 2026.
CAT publishes a genuine replacement-pump decision framework
CAT is especially valuable for PressureWasherMatch.com because its pressure-washer documentation does more than publish PSI and GPM. Technical Bulletin 129 tells users to verify the engine-side interface first: horizontal shaft, straight/keyed shaft style, diameter and nominal speed, then confirm available engine torque at the required RPM.
That makes CAT a strong manufacturer page rather than a product-list page. Use the Honda-powered guide when the engine is identified by Honda family, then continue to the Pump Finder.
Current CAT direct-drive pressure-washer classes
| CAT model | Flow / pressure | Shaft / RPM | Ports | Fitment class |
|---|---|---|---|---|
| 4DNX25GSI | 2.5 GPM / 3000 PSI | 3/4-in straight horizontal / 3450 RPM | 3/4-in GH(F) inlet; 3/8-in NPT(M) discharge | Compact direct-drive replacement class. |
| 4DNX27GSI | 2.7 GPM / 3000 PSI | 3/4-in straight horizontal / 3450 RPM | 3/4-in GH(F) inlet; 3/8-in NPT(M) discharge | Same shaft class with slightly higher flow. |
| 66DX35G1I | 3.5 GPM / 4000 PSI | 1-in straight horizontal / 3400 RPM | 1/2-in NPT(F) inlet; 3/8-in NPT(M) discharge | Higher-pressure 1-in direct-drive class. |
| 66DX40G1I | 4.0 GPM / 4000 PSI | 1-in straight horizontal / 3400 RPM | 1/2-in NPT(F) inlet; 3/8-in NPT(M) discharge | Professional 4-GPM direct-drive class. |
Even within one manufacturer, shaft diameter and plumbing differ materially. A 4DNX and 66DX are not interchangeable “CAT pumps.”
Engine torque is a compatibility input
CAT publishes the relationship Torque required = 3.6 × (GPM × PSI) / RPM in its direct-drive replacement bulletin and tells users to consult the engine manufacturer for actual torque at the required speed. That is why a physically matching 1-inch pump can still overload an engine.
Use the replacement-pump checklist for the rest of the mounting, unloader and clearance checks.
CAT 4DNX options only after the 3/4-inch class is verified
If your engine is a straight 3/4-inch horizontal shaft and the required output/RPM align with the 4DNX class, compare current 4DNX listings only after checking engine torque and installation clearance.
Manufacturer sources
- CAT Pumps — pressure-wash pumps — Current pressure-washing product families and popular models.
- CAT Pumps — 4DNX25GSI — 2.5 GPM / 3000 PSI / 3/4-in straight horizontal shaft / 3450 RPM.
- CAT Pumps — 4DNX27GSI — 2.7 GPM / 3000 PSI direct-drive reference.
- CAT Pumps — 66DX40G1I — 4.0 GPM / 4000 PSI / 1-in straight horizontal shaft / 3400 RPM.
- CAT Pumps — Technical Bulletin 129 — Replacement pressure-washer pump shaft, RPM and torque-selection guidance.
Sources reviewed August 28, 2026. PressureWasherMatch.com is independent and is not affiliated with or endorsed by the manufacturers referenced above.
Frequently asked questions
Which CAT pressure washer pump fits a 3/4-inch horizontal engine shaft?
CAT currently lists 4DNX direct-drive models for 3/4-inch straight horizontal shafts, including 4DNX25GSI and 4DNX27GSI. Final selection still requires engine torque, RPM, mounting and plumbing checks.
What CAT pump is rated for 4 GPM and 4000 PSI?
The current CAT 66DX40G1I is rated 4.0 GPM at 4000 PSI and is designed for a 1-inch straight horizontal gas-engine shaft at 3400 RPM.
Can I replace any factory pump with a CAT pump if PSI and GPM are close?
No. CAT Technical Bulletin 129 says to confirm a horizontal straight keyed shaft, shaft diameter, nominal RPM and engine torque before selecting a direct-drive replacement.
What is the difference between CAT 4DNX and 66DX?
The 4DNX pressure-washer models are compact 3/4-inch-shaft direct-drive pumps around 2.5 to 2.7 GPM at 3000 PSI. The 66DX family includes 1-inch-shaft direct-drive models at higher flow/pressure classes, including 4 GPM at 4000 PSI.
Does a CAT pump include an unloader?
Specific configurations differ. Current 4DNX GSI data describes an integral pressure unloader with bypass, while other CAT families and configurations may use different control arrangements. Verify the exact model suffix and datasheet.
Can the Pressure Washer Pump Finder verify a CAT replacement?
The finder includes an initial CAT 4DNX record, but final compatibility still depends on the exact engine, shaft, mount, power, ports and clearance. Unknown or conditional is preferable to guessing.