Which pump oil for Karcher HD 3500 pressure washer

[i6pwr]

I bought it used, the fill cap on the pump reads....

"Motoren Oel 15W/40"

Obviously it's in the German form but is this regular motor oil or non-detergent oil?

This is not the engine oil fill cap.

Motor is GX390 Honda.

 

[i6pwr]

I called Karcher, actually open today and they said it's non-detergent oil.

 

[Rand]

I usually use Cat brand Pump oil but that's a high end unit you have there.

http://www.homedepot.com/p/Cat-Pumps-21-oz-Pressure-Washer-Pump-Oil-AP31045/202021265

 

[CT8]

I use 75w-90 gear oil

 

[i6pwr]

I had some 30W non-detergent pump oil I thought I used up and tried that. Turns out the pump is surging and is leaking pump oil. Appears to be an O-ring but the surging is another issue. I tried to find the unloader valve but for the life of me I cannot locate it.

 

[bubbatime]

Did their US affiliate recommend a replacement oil, since 15W40 non detergent would be very hard to find in North America?