"Best" synthetic hydraulic fluid for the money?

[KMA]

Good idea. I will definitely try my best to do that.

Okay... due to time constraints and having to get the full oil change done quickly in order to do work around the house, I wasn't able to do any tests that would even remotely be considered "scientific". I apologize.

The good news is, I've been using the Rotella T Synthetic 5w-40 oil in my PT-422 for a few months, and I think I have noticed a positive improvement. I've been using the brush hog a lot recently, and it's been in the upper 80's many of the days. Needless to say, the machine is getting about as hot as it gets. I noticed when I return back up the hill to my garage, I'm able to travel at the fastest forward speed the machine is capable of. In other words, there is no noticeable different in ground speed when the hydraulic oil is cool or hot. Prior to changing the oil, I noticed a "slowdown" when the oil heated up, but that is no longer the case. Also (although I can't be 100% sure), it seems the pumps make less of that "screaching" type noise I would sometimes hear.

Again, not very scientific but I really think the machine/oil is performing much better overall. Hope this helps.

 

[Wayne County Hose]

Sounds like it was worth the money.

 

[MuncyBob]

Thanks for the update....sounds like a possible way for me to go on my next filter change. On the next filter change I plan to change the fluid and install a gasket to eliminate the crud build up on the tank top.

On a side note....I think I recently experienced vapor lock on a very hot day after 2 hours of mowing...only happened when going downhill though. I could feel her start to sputter and did actually stall once. I think I'll try to better insulate the fuel line(wrapped in aluminum foil now) or look to see about replacing the fuel line with a ready made insulated line.

 

[Bob999]

I've been using the Rotella T Synthetic 5w-40 oil in my PT-422 for a few months, and I think I have noticed a positive improvement. I've been using the brush hog a lot recently, and it's been in the upper 80's many of the days. Needless to say, the machine is getting about as hot as it gets. I noticed when I return back up the hill to my garage, I'm able to travel at the fastest forward speed the machine is capable of. In other words, there is no noticeable different in ground speed when the hydraulic oil is cool or hot. Prior to changing the oil, I noticed a "slowdown" when the oil heated up, but that is no longer the case. Also (although I can't be 100% sure), it seems the pumps make less of that "screaching" type noise I would sometimes hear.

I think that an additional advantage us using 5w-40 oil is the reduced viscosity at low temperatures. Pt uses a suction side filter for the variable displacement pump. The advantage of suction side filters is that the provide direct protection. the disadvantage is that the flow restriction can, if it is excessive, cause cavitation in the pump. I think it is concern about cavitation that is the basis for the very frequent change interval (50 hours) for the hydraulic filter.

I installed a vacuum gage on the hydraulic filter and the highest vacuum occurs when the oil is cold--as much as 20" with cold oil and high engine speed. By comparison with warm oil and full throttle I only get a vacuum of about 3". I see essentially no change in vacuum readings between a clean filter and one with 50 hours on it.