Re: Rtv-900x
The transmissions on these are notorious for "issues".
"Issues" in quotes because there's nothing wrong with them 99.9% of the time, just owner hasn't gotten used to them-and the characteristics of an HST in this application.
The HST uses a lot of horsepower. The HST is also dependent (severely) on temperature. Hot oil's viscosity is much lower than cold oil. Hot "thin" oil will bypass through the HST without doing as much work, and the opposite happens with cold "thick" oil.
They are very viscosity temperamental. Similarly, if a "cheap" hydraulic oil-even Kubota UDT, is used, and the unit is used in cold climates, the HST will bog the engine to the point where it it totally gutless. Super UDT only in HST's and the more temperate the climate, the more dependent they are on GOOD hydraulic fluid!
Some bogging is going to be normal by design, just like a tractor.
Additionally, they're extremely sensitive to proper cable adjustments. Also they're bad sensitive to charge pressure. 1 or 2 psi either way of the specification will either make it pull harder and faster or it'll "slip" a ton and barely move. That's why an accurate digital pressure gauge is required for anyone who's got to work on these things.
And finally, since a diesel engine is dependent on the air going into the engine, at higher altitudes, the engine's horsepower and torque will drop significantly, which affects the HST performance, which affects the engine output, which affects the HST performance. It's a snowball effect. If using yours at altitude, I suggest a turbo kit. The turbo forces the air into the engine at the same pressure (more or less) regardless of the altitude, so the power loss between sea level and 10k feet is drastically reduced! We see this OFTEN as spring fades into Summer, right about May, and people start calling about (1) power loss and (2) overheating.
Use low range if you're going to be under 5 mph. Keeps heat in the transmission to a minimum. More than 7-10 mph sustained on flat ground with low loading, you can use high. If used in hills, low gear. Climbing over tree stumps, ditch banks, whatever, low gear. Low is just another gear in the transmission. Think of it as first and second, where first is low and second is high. It won't hurt it to run it in low gear against the governor, and actually is good to do that sometimes since the engine's designed for max speed/max load (like a BX engine-and actually it's almost identical to some of the BX tractor engines and lawn mower engines).
Couple years ago I had a customer ask about a turbo kit. Said he wanted to go faster. It was already topping out at 26 mph (RTV-X1100) with the A/C off. That is pretty good. I advised him that the turbo won't make it any faster because the engine is governed and it simply can't go any faster, period. HOWEVER, we put it on anyway, and he cussed because it was not faster-not at all (still 25-26mph). This cussing went on for almost a year. Then this past September he called me from the hills out in Western Colorado, said he was HIGHLY impressed with the turbo's ability to still maintain almost 25mph even up there where it was hard to breathe. Said there was a gentleman with an X900 and the X1100 turbo was faster (and they're usually slower) than the X900 if they're both unmodified. The before and after turbo kit on flat parking lot, there is no difference in power. Where you see the difference is in altitude and weather swings, and with those if you put a stock RTV against a turbo RTV, there is a HUGE difference.