Glad to hear that someone has gone to Transynd without issue. Thanks for that info Bill. That will certainly last longer then Dexron but it leaves you with the dilemma when if ever should you change it again.
Fred, I agree an ounce of prevention is worth a pound of cure always. That being said I do not want to throw money down the drain by changing fluid that is in excellent condition. I know after 20 years, which seems a bit crazy I admit, but the fluid looked just like new fluid every time I changed the filter. I would go to change the filter with the intent of changing the fluid and just take a pass until next time given it looked perfect. I also was in that Dexron 1, 2,3, 4 etc dilemma. I never replaced any component in that system. So forgetting the change interval how concerned should I be at 90K miles?
I did some calculations and estimated that in 90K miles I had about 2000 operating hours on the pump and system. I went and did a search and pulled up a PDF on a mini Cat hydraulic excavator with a small backhoe which has to be working harder with more heat generated for the fluid then our hydraulics. Cat call for a hydraulic fluid change at 2000 hours/2 years for standard fluid and 3000hrs/18 months for Hydro Advanced or 6000 hours/3 years with SOS analysis unless you are using a hydraulic driven hammer attachment. I think the interval in years is driven by the possibility of condensation being introduced.
I find Cat to be pretty conservative in general with maintenance intervals. They generate the service intervals based on fluid analysis. Without a contaminant issue or condensation issue this fluid probably has a useful life of 100K miles or more would be a reasonable estimate. This is one of those fluids where oil analysis would really help.
Later Ed