Hi folks,
Just to share the facts and data, I'm a strong advocate of oil testing as a way to gain insights about what is really going on. In my case, I was especially interested in the transaxle oil since my first test show such poor results:
http://hiwaay.net/~bzwilson/prius/pri_T_cold.html
http://hiwaay.net/~bzwilson/prius/pri_toil.html
These oil tests are affordable, about $20 but to shorten the interval takes many more samples. I asked for used oil samples and paid for many of the tests, a small scale version of our hybrid vehicle database. But at last, there is data supporting a shorter change interval for the NHW11.
Since then, I've learned from an SAE paper about a better approach that does on-vehicle viscosity testing. It records the oil temperature and pressure at idle, using the existing engine as a viscosity test instrument. This is an approach I'll be investigating in the future for both engine and transaxle oil testing.
What I'm trying to suggest is:
- respect the warranty - until the engine warranty has expired, follow the manufacturer's recommendation and keep good records
- post-warranty - use oil testing to determine what is going on and needs to be done to keep the engine happy
GOOD LUCK!
Bob Wilson