Nope. Once the system is pressurized, neither gravity or orientation have much of an effect. Many commercial applications have hydraulic filters mounted "upside down" and the only issue is the one you describe (changing filter mess and the inability to pre-fill the filter). Trapping air or bypassing filtration are of no concern once the system pressurizes. You'll read some misinformation on ADBV function online when a filter is mounted this way, but ignore that mess.....the ADBV's function is NOT to prevent drainage of oil out of the filter as some might declare. In fact, many Toyotas (and I'm sure others) come from the factory with "upside down" oil filters.
Thanks Hood. I figured as much but wanted some confirmation. The only other thing I could think might be an issue is structural problems of the housing mount itself with the leverage the filter would have on it mounted sideways with bumps and vibrations. Opposed to the filter hanging down. Don't know if there is any merit to that line of thought though.
After my transmission failure, I put an additional in-line transmission filter near my transmission auxillary cooler. I purchased a in-line trans filter from NAPA that has a magnet in the filter. It looks similar to a small fuel filter and has a diretion of flow so it needs to be installed correclty. I appoligize that I don't currently have a part number..I'll find it later. It cost 27.99 and I think it's a good idea to have this filter. An oz of prevention is worth a pound of cure![]()