you should be more worried about your pump than the GC160 Honda.
I have a "Pressure Wave" power washer with the 5.5 hp Honda GC160.
The pump went out after 2.5 years. I had an extended warranty so it was covered.
The owner of the repair shop told me to maintain the pump to guard against corrosion and hard water deposit build up in the pump which led to it's failure.
When you are done with the unit for the day, tip it forward and try to let the water drip out of the input of the pump.
Also rig up a funnel connected to a 3 foot piece of garden hose and connect it to the input of the pump. Pour some antifreeze in it and fill up the pump.
Or buy the aerosol can of pump cleaner/protectanct that has a hose connection. It connects up and you can spray it into the pump.
As for the Honda GC 160, thats a very very common Honda engine. It's put on genorators, mowers, washers, pumps, etc etc.
Right now mine has MoCraft 5-20 with a good shot of Valvoline Synthetic Oil Boost. I change it out when it discolors bad or every season, which ever comes first.
If I still had my Maxlife stash, I would use that.
Try Valvoline MaxLife HD 30 or 10-30. Perfect for you application!