What would be the preferred method of flushing the hydraulic system of milky, water contaminated hydraulic oil on a Cat 920 wheel loader?
The answer is "it depends"........ It depends how bad the oil is that's in there right now, and it depends on how much effort you are prepare to put in to get oil out of components in the hydraulic system, not just what's in the tank. Attached is the procedure for changing the hydraulic oil. What I would suggest is to use that, but after Step 9 disconnect the hoses to the lift and tilt cylinders and drain the old oil out from the hoses in addition to draining the tank. You'll need to be careful when refilling the system because it will take more oil than the manual suggests due to the lines having been drained. You may well find that the oil is still slightly discoloured even after doing it this way and you may find it necessary to repeat the oil change at some future date.
I forgot to mention that in addition to draining the oil from the cylinder lines you could also leave certain hose connections loose so that when the cylinders are exercised for the 1st time you could drain any contaminted oil that remains in the cylinders or lines into an external contianer without having it return to tank. As I said before, it's all down to how much effort you want to put into it.
Might be a bit paranoid, but even if oil looks good after one change I would be very tempted to at least change filter once or twice after running a short time. Not sure if the media or glues in the filter are compatible with water. Last thing you need is to have a chunk of filter media floating around in the system!
Ok thanks guys. The loader sat outside for 7 or 8 yrs with a bad engine, and I’m just getting things back in working order.
Be prepared for a slog because getting all the contaminated oil out at the first attempt is going to be difficult. KSH had a good suggestion regarding the filters. You might well end up changing it half a dozen times but if it prevents a hard failure it has to be worth it.
I'd like to try a do it yourself version of vacuum dehydration, or other bulk water removal like bubbling hot air through the oil. Get it set up on or near the machine, run the reservoir oil through the filter, use the machine a while, repeat the process until you are satisfied ALL the oil is dry. Then change it. It's on the list when I get the time.
I think I would be a little worried about running that machine around here the last few days if it was parked outside. Temps in the low single digits ºF. Not sure what ice would do to pumps and or hydraulic valves. Just starting a machine with nice clean hydraulic oil can be touchy at those temps if not allowed to warm up a bit before moving anything!
While I’m draining the tank/system, can I remove all the bolts on the tank in order to access the sight window? Mine is all discolored and cannot be seen through.
With the tank empty that would be the best time to get into it and replace the sight glass window and the seal, because you can bet if you disturb it and don't replace the seal, it's guaranteed to leak........
Sight Glass should be # 4J8252 and the grommet(seal) should be # 4J8251 And assuming you are removing the large side cover the sight glass is mounted in you would need gasket # 6J7376 SIS shows three different tank assemblies for the 920 but I checked all of them and they all use the same side cover gasket.
Perfect. I’ll get them ordered. On an unrelated note, is the dipstick for the fuel tank 3V7042? They’re calling it a “plunger” so I wasn’t sure. Thanks again.
Had to go look and yes Cat is calling it a "Plunger" guess someone thought calling it a dipstick was a derogatory term!
Lol! Thanks for checking