Simpson Aluminum Series 4200 PSI Gas Pressure Washer, 4.0 GPM, Honda GX390

The SIMPSON Aluminum Series gas pressure washer delivers heavy-duty power designed for contractors and demanding outdoor cleaning tasks. Built around a Honda GX390 gas engine and a CAT triplex plunger pump, this cold water machine pumps out 4200 PSI at 4.0 GPM. It provides the water volume and force needed to clean driveways, decks, siding, equipment, fencing, and stubborn graffiti.

At the heart of the setup is a drive system engineered for heavy workloads. The Honda engine includes a low-oil shutdown feature to guard against engine damage, while the CAT triplex pump utilizes ceramic-coated pistons and advanced oil seal technology for long operational life. A built-in thermal relief system helps prevent the pump from overheating during extended idling periods. The machine comes equipped with a 50-foot dual-braided high-pressure hose that resists kinks and abrasion. Its non-marring polyurethane outer jacket helps protect clean driveways, stained wood, and painted surfaces while you work.

Mobility and frame design focus on practical job site handling. An aircraft-grade aluminum frame keeps structural strength high while resisting rust, protected further by a powder-coated finish. Large 13-inch pneumatic tires combined with a balanced frame layout allow you to roll the machine across gravel, lawn, and over curbs without tipping. The included accessory package features five quick-connect nozzles (0, 15, 25, 40 degrees, plus a soap nozzle), a professional spray gun with a safety lock-out, and a 16-inch spray wand.

While built for performance, there are practical trade-offs to keep in mind. At 133 pounds, moving this pressure washer into truck beds or up stairs requires substantial physical effort. This model is a cold water unit, so it relies solely on water pressure and detergent rather than heated water. Additionally, it is 49-state compliant and cannot be sold or shipped into California.

Verdict: This SIMPSON gas pressure washer is an ideal choice for contractors and commercial users who need maximum cleaning force and high water volume for tough job sites. Its combination of a proven Honda engine, durable triplex pump, and sturdy aluminum frame makes it a solid investment for heavy cleaning.

• Engine: HONDA GX390 with low-oil shutdown
• Pressure Output: 4200 PSI
• Flow Rate: 4.0 GPM
• Pump Type: CAT triplex plunger pump with thermal relief
• Frame Material: Aircraft grade aluminum with powder-coated finish
• Hose: 50-foot dual-braided high-pressure hose (M22 connection)
• Tires: 13-inch pneumatic tires
• Dimensions: 38 in L x 23.5 in W x 29 in H
• Weight: 133 lb
• Included Nozzles: 5 quick-connect tips (0°, 15°, 25°, 40°, soap)

A great fit if you:

• Need high water volume and pressure to strip paint, clean equipment, or remove graffiti
• Want a commercial-grade Honda GX390 gas engine with low-oil protection
• Require a durable aluminum frame that resists rust when working outdoors
• Work on rough job sites with gravel, grass, or curbs that require large pneumatic tires

Consider something else if you:

• Live in California, where this 49-state compliant model cannot be sold
• Need a lightweight pressure washer that is easy for one person to lift into a car trunk
• Require hot water cleaning capability for specialized grease removal tasks

Is this pressure washer available for purchase in California?
No, this machine is 49-state compliant and is explicitly listed as not for sale in California.

What accessories are included in the package?
The pressure washer includes a 50-foot dual-braided high-pressure hose, a professional quick-connect spray gun with a safety lock-out, a 16-inch spray wand, and five quick-connect nozzles ranging from 0 degrees to soap application.

What engine protection features are built into this model?
The Honda GX390 engine includes a low-oil shutdown feature to prevent engine damage if oil drops below safe operating levels.

How portable is this machine on rough job sites?
It features 13-inch pneumatic tires and a balanced aircraft-grade aluminum frame to roll smoothly over gravel, grass, and curbs despite its 133-pound weight.