GX390 for heavy use homeowner

Hi, new to the group and trying to learn so I would appreciate everyone’s opinions. I have a GX390 and my AR RSV direct engine pump just died so looking to replace the pump.

The pressure washer will only be for personal use doing cement driveways, my wood dock and I clean 4 wheelers that I flip daily. I would like a 4GPM 4,000 PSI pump or somewhere around that and just change the tips for low PSI usage when I clean the 4wheelers.

I have really bad luck with products so I would like a pump with a great warranty. Also a good place to purchase would be helpful as well.

Any recommendations would be appreciated. Thanks!

Look up UDOR in the magnifying glass

Gp is fine. Cat is better udor is best but it makes little difference on the low gpm machines, if you were using 8Gpm+ Id say spend the extra on an udor.

I ended up going with a General Pump EZ4040G. It is much larger physically than my old AR pump. I got it bolted up today but didn’t see a relief valve (pisser) or the soap injector. Do I need to add these things myself? Where on the pump would they install? Is it safe to run the pump without them? I’d appreciate some guidance before I fire it up the first time. The pump came with no directions at all.

Photos for reference

“Real” pumps don’t come with built in injectors. I would recommend the GP Hi-Draw injector. Put a short whip line between the unloader and the injector. That will smooth out some of the turbulent flow from the pump, improving injector performance, and purportedly it protects your pump in the rare instance that the injector fails somehow and allows chems to back-siphon.

Drop your injector pickup tube in a bucket of clean water when you’re done soaping, and it will last much longer. But you should still order a spare.

The unloader on your pump recycles the water back to the inlet, so you have to be diligent about keeping the trigger pulled for most of the time the pump is running. Don’t let off the trigger for more than a minute at a time, as the recirculated water will heat up quickly and shorten the life of the pump.

(The easy solution for us pros is to have the unloader bypass to our buffer tank, so it’s always pulling cool water through the pump. I don’t worry at all about staying on the trigger)

The little white cap looking thing is a safety valve. Pretty sure it is temperature and pressure sensitive. If it fails, don’t just plug it. When it goes out, it’s saying, “I just did my job and saved your pump.”

Hope that helps. Congrats on your purchase :wink:


I was going to reply to help out but I think you covered just about everything.

Thanks for the help, i’ll look into ordering the injector. I do have another question. My spray gun came with a 1/4" Female to 3/8" male fitting. Where could I find a 1/4" female to 3/8" female fitting so I can connect my hose? The female end of my hose is connected to the pump and I can’t get the male end of the hose off to make both sides female.

Guys, don’t answer this nonsense.

Why not?

Most hoses come with male ends and not female. If the hose and gun came off of a homeowner unit it might have female ends. If so make sure the fitting isn’t actually a M22 to 3/8". Just something to check. If it is an actual fitting that is so corroded it won’t come loose you are probably better off ditching it and getting a new hose and possibly gun.

A 1/4" female to 3/8" male is called a bushing. You can get bushings at any hardware store but check with a place that sells jic hydraulic fittings. A lot of fittings aren’t rated for much pressure but jic will be. My local Napa makes hoses and sells fittings. I’ve even been to my local John Deere dealership to get fittings. Farm stores normally have them too. If anything, just order online.