Rust Scale Remover


New Member
I just ended up with a Dewalt DP38. 3800/4.0. Has a Honda GX390 with cat 67dx39g1l pump. The prior owner I think left it full of water often enough to let rust and gunk build up. The unloader was a mess full of rust gunk etc. Bit of cleaning and some marin grade waterproof grease and the the pressure can easily be adjusted down to 1k psi now. Ive used it and it runs well, bit of blue smoke on cold start, but after that its pushing 3500 psi. With all that water flowing its a cleaning beast.

I would like to clean the pump out without pulling it apart. Thinking maybe some evapo - rust flush, but not sure how to get this in the intake water feed. Any ideas when your not running a tank setup, to get the evapo rust in there? Would it pull water from a bucket setup (loop the intake and output to a five gallon bucket filled with evapo rust solution.)

Also, prior owner pulled the thermo relief valve off and just put on a regular ball valve. For residential use is the thermo valve a big deal?



Moderator / Sponsor
I would just hook water hose to unit, and flush with water, without HP hose, and gun.

The thermal relief valve, prevents overheating of pump when left in bypass.


New Member
Tnanks fod the thoughts Mark.
I had some time so I pulled the couplers off the pump and put a bore scope in the pump. It looks very clean, the rust build up was limited to the input and output coupler. Bore brush and they look good enough.

This being a new machine to me but used and unknown maintenance, I changed the oil in motor and pump, new spark plug, air filter, and quick conects for the hose as they were not ao quick to uncouple.

What other things should I check to ensure good performance from here on out? Honda gx390 and cat pump 67DX39G1L.

Thank you


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