Kubota RTV slow on hills when warm: HST fluid and filter
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Applies to: Kubota RTV1140CPX and other hydrostatic RTVs
Symptoms
- Fine when cold, slow on hills once warm
- Whine from the transmission
- Top speed drops under load
Why it happens
The hydrostatic transmission shares fluid with the hydraulics. Low or old fluid, the wrong fluid, or a clogged filter cuts pressure as the oil heats up.
How to fix it
- Check fluid level on level ground with the engine off.
- Change the hydraulic filter and fluid with the type the manual specifies.
- Check the speed control linkage for full travel.
- Check that the tow/bypass valve is fully closed.
Tools and parts
- Transmission fluid per manual
- Hydraulic filter
- Drain pan
What the factory service manual covers
Hydrostatic transmission: fluid spec and capacity, pressure tests, linkage adjustment. The full procedure, specs and wiring diagrams are in the factory service manual for your machine.