Transaxle Fluid. Do I Change It Or Leave It Alone?

Welcome Lex;
The car nut is speaking about a normal transmission with valve bodies and wet clutches NOT a hybrid CVT.
I'm of the opinion that you should change it, just to remove the break-in wear material and other nasties floating around in there. Actually your transmission is working harder than a normal transmission, because of the two electric motors within. Your transmission may work independent of your ICE and move the car up to 10 mph before requiring the ICE to kick in.
While the transmission on these cars don't fail too often, I just like to give it a leg up and consider it cheap insurance.

Hope this helps....

 

I agree, go ahead with the change....it's as easy as doing an oil change BUT be ready for very tight hex bolts if they haven't been open in 12 years. (My Gen 4's have 10mm hex bolts.)
I found it easier to snake a tube down the back of the engine bay to refill mine instead of pumping up the fluid...I hate those hand pumps.

 

if you are keeping the car long term, change it. if not, i wouldn't bother, these transaxles are almost bulletproof

 

The type of work matters a lot.

The Prius transaxle does not contain any clutches, bands, belts, drums or other friction systems. Therefore no particles are ever shed into the fluid.

This is fundamentally different from most automatic transmissions, and it's the reason why these cars can go a zillionty miles on the factory ATF.

If you do change it, insist on the real-deal Toyota WS ATF. I'm sure many other ATFs would provide the right lubrication, but personally I would not take the risk that they might eat the insulation off the windings of the motor-generators in there.

 

About one year or 10k is about right for that. Then you can leave it much longer, say once more at 100k or 10 years.

@Lexington-76: yes, by all means change it. There’s a relevant link in my signature; on a phone turn it landscape to see signatures.

 

Dealership parts department. Ditto for the fill/drain bolt washers.

BTW, just woke up, to you’re having a Prius c. Still, the procedure should be very similar. You might want to take out a short term subscription at Toyota Tech Info, get the precise instruction. It may not exist; Toyota did NOT provide an instruction for Gen 2, but they do for Gen 3 and 4.

My hunch, it’ll be fine. For sure fill with the car level till it starts coming back out, you’re good.

 

Like others have said, the Prius eCVT transmission is completely different than a normal car transmission. Beside the two electric motors, it has just metal gears and bearings. Metal particles shed by the gears are caught by a magnet at the bottom of the transmission case but, in this transmission, you can't access this magnet so even if you change the transmission fluid, they'll all remain on the magnet. Basically the only thing that could be floating in the fluid is the motor winding insulation but if you have that, you have a bigger issue lingering.

 

Lexington: ICE stands for Internal Combustion Engine. It's how Hybrid folks differentiate when talking about engines...kinda like how motorcycle riders call car drivers "cagers" Electric engines can have all kinds of different names but Toyota seems to like electric motor generator or MG...I'm not certain but believe all Prius' have an MG1 and an MG2. You may see traction motor or generator motor (or both in a Honda).
A quart of Toyota WS is between $5-9 a quart...my 2017 took 3 3/4 for the service. I bought 5 so will only need to buy 3 when I do my 2021 Prius which is coming up on 50,000 miles.

 

My 2012 Prius C took a bit more than 3, so I'd grab 4 quart to be safe. Your correct, those fill and drain plugs are very tight out of the factory. They're only suppose to be 37 ft/lb. If you do it yourself, 10mm hex socket w/1/2in breaker bar and scrape all the dirt out of those hexes with an ice pick, before trying. Plant the socket in firmly and push or stomp on it.

Hope this helps...

FYI: those electric motors in the tranny are also chargers for your batteries and starter for your engine - so a critical component of that car.

 

Since the value may be used for torquing: with Gen 2 and 3 the Repair Manual spec is 29 ft/lb. With Gen 4 it's 37 ft/lb. That's all I've got, haven't got the Prius v or c.

Unless OP checks on Toyota Tech Info, looks up the Prius c info, probably best to stick with 29 ft/lb. Which is still tough to bust loose. Again, I go straight to an over-long ratchet I have (about 18" from fulcrum to end of handle), With a reducer to 3/8" drive and a proper 10 mm hex driver "socket".

You definitely don't want to use a L-shaped hex key with a pipe extension. Doubly so, don't try a 3/8" instead of 10 mm.

BTW: Honda uses a similar socket head cap screw on their transmission drains, but with a 3/8" square recess. I remember over 40 years ago, very green, going to attempt changing the transmission fluid on our '81 Civic: saw that, phoned up the dealership, and asked what special socket was required. The guy went down to the shop to ask a mechanic, got back to the phone and told me something like "they just use a 3/8" drive ratchet wrench without a socket".

See attached Repair Manual excerpts, for aforementioned torque values, and just to get a feel for what's involved.