How to change the filter for transmission/hydraulic oil without changing oil?

[k0ua]

I also wondered about the oil vapor passing thru the vacuum motor. The air bubbles coming in thru the open hole at the filter outlet cause the bubbles to form and pop at the top of the reservoir and the vapor does get sucked into the vacuum and deposit an oily film inside. That is why I stopped using the vacuum method. I think my stop up the vent idea is at least as good, not messy and no risk.

 

[Captain Dirty]

I also wondered about the oil vapor passing thru the vacuum motor. The air bubbles coming in thru the open hole at the filter outlet cause the bubbles to form and pop at the top of the reservoir and the vapor does get sucked into the vacuum and deposit an oily film inside. That is why I stopped using the vacuum method. I think my stop up the vent idea is at least as good, not messy and no risk.

Admittedly, I had discounted "sucked fluid into the vac" as my method would have shown liquid in the tube in time to break the suction; I had not considered hydraulic oil vapors igniting in the shop vac. I did not notice any oily film, but then I was not looking for it. While there is no such thing as a "no risk" situation, I would expect that much of any oily film would be deposited on the inside of the corrugated hose or the exterior of the filter. Thus, the likelihood of a combustible oil-air mixture at the brushes would be small. Further, if one had the filters at hand and was prepared to quickly change them the time of exposure would be short. If one left the vac running while getting the filters, answering phone calls, etc. then more vapors would be sucked up.

If oil analysis recommends filter change only at the next 400 hours I will try your plugged vent method.

 

[Macinnis]

They make oil extractors for as little as $25 on Amazon...you hook it up to your battery, connect the tube, put it in the hole and it sucks as much out as it can. Sounds like you would need 3-4 5gallon buckets with lids to store it clean.

Then do your filter change and add it back in. I have one for my boat and it’s a life saver as you literally can not get under the engine to drain the oil.

 

[Captain Dirty]

I would use vice-grips and small blocks of wood to pinch the vent hose. Murphy says any screw I used would let just enough air by to get at least a good burp. The pliers would be more obvious next to the fill hole than K0ua's #8 screw head. I have the vice-grips, no oil extractor. The 5-gallon pails would be a recurring expense as I would, no doubt, store some contaminant in them between service intervals.

 

[k0ua]

A golf Tee would probably work well too, and an orange one would be a good reminder to pull it out when done. Give it a try and see what you think. And no, I didn't have any "explosions" with the vacuum cleaner either, but the hose certainly had an oily film inside. In any case the "stop up the vent" method has worked well for me.