Is there a Downside to Changing Transaxle fluid?

nope. you just need to make sure that 4 quarts of genuine WS fluid are used for the change. could be your guy used the wrong fluid. there is a magnet on the drain plug which should catch all the metal particles in the fluid. good idea to do it every 60k.

 

Doubt very much a proper change would have any downside. That assumes:

1. You get the correct Toyota fluid.
2. You change the drain and fill bolt washers.
3. You torque both bolts correctly. (not sure of gen 2 torque requirement)
4. You follow the procedure outlined in the Repair Manual. I believe it's similar to gen 3, in that you get the car raised and level, and pour in fluid 'till it starts coming back out.

 

The big difference between the Prius and any other transmission is that the Prius has high voltage electric motors running in the oil (there are other differences). If that oil conducts electricity the motors burn out or a high voltage ground leak is detected by the computers and shuts the car down. The correct oil must be used.

John

 

Your service guy is not knowledgeable enough about the Prius. As Briprius noted above, this service guy probably used whatever Dexron ATF lying around. Even if he used Toyota ATF-WS, coincidence's happen. It could have easily been, not changing the transaxle fluid produced the same problem. Did this service guy tell you what the resulting problem was?

Your son is mistaken. Metal particles are always breaking off and floating around in the fluid. These metal particles will likely find their way between the fine workings of the "gears," causing unnecessary wear. Imagine two gears w/ oil; no issues, well lubricated, long life expected. Now add some metal shavings in this example; accelerated wear because the metal particles are floating freely, grinding down the gears faster than they would w/o these metal particles. A magnetic drain plug helps capture these metal particles to reduce wear; Gen2 Prius has a magnetic drain plug, albeit a weak one.

Have your son read this study. He will likely appreciate it and become further enlightened about this topic.
Transaxle oil, recent analysis | PriusChat

Everyone knows NO LUBRICANT LASTS FOREVER. No one questions engine oil and engine oil filter being changed at specified intervals. Why do they question the transaxle? Thank Toyota listing ATF-WS as a lifetime fluid that only requires "checking" and "refilling" if nececessary. Toyota's idea of "lifetime," will be vastly different than the average consumer's view of "lifetime." All auto manufactures want their cars to last just long enough w/ "minimal" maintenance, before the car falls apart, AFTER all warranty is over. Now the consumer is left with repairs that may be costly, or put this money towards a new car.

Read this from Art's Automotive. It really highlights the reality of Manufacture's Maintenance Schedule being a MINIMUM.
Prius 30k Service

Read post #473, you will likely be convinced, that transaxle fluid changes are a good thing.
ATF fluid changes ARE Required. | Page 24 | PriusChat

A well maintained car sells easier than a poorly maintained car.

Since you drive so little, you may want to get a Grid Charger.
Hybrid Battery Preventative Maintenance Grid Charger for 2004-2009 Toyota Prius - PriusChat Shop
There are various threads about this item in Gen2 section.

 

Has anyone posted, or could post, second Gen Repair Manual excerpt for Transaxle fluid replacement. I've got third gen, but there are some differences, the fill and drain bolts are different, likely different torque.

FWIW, on third gen both bolts are the same, and torque is 29 lb/ft. Fluid is:

TOYOTA ATF WS (4 liters is more than enough. With car level, add fluid 'till it starts coming back out.)

 

Gen2 uses same 29 FOOT-Pound, as your Gen3.

EDIT: Toyota manual only lists the FILL PLUG as 29FT-LB. No mention of DRAIN PLUG torque. Its assumed 29FT-LB. Bentley manual does list FILL and DRAIN PLUG as 29FT-LB each.

 

"IF" the transmission failed due to a fluid change, assuming it was done correctly and with the proper "spec'ed" fluid, then the transmission was already toast.

 

congrats and welcome! i don't recall a problem ever being reported here, but with your driving, i'd save my money for a new hybrid battery. all the best!

 

There is no problem changing the transaxle ATF assuming this is done correctly (a simple drain and replace is all that is required) and the correct Toyota ATF WS (4 quarts) is used.

Since your driving is so limited, I suggest you connect the 12V battery to a charger 2x per month, overnight, or else use a battery tender. Otherwise you will find the 12V battery's service life will be pretty short.

 

Id do it ASAP, then a longer interval. The initial wear is worst.

 

One caution, always loosen the fill plug before opening the drain plug.
If you were to drain all the ATF WS and then discover you could not open the fill plug, you would be in a 'tow truck' event.

 

I changed my transaxle fluid at 36k miles, and the fluid was very dark, almost opaque. I plan on changing it at 100k next.

 

Ditto what xliderider said, except that I changed mine at about 48,500. The old stuff came out inky black (but thankfully not chunky or gritty).