Transmission Oil Change

The trans axle fluid drain and fill is an easy job to perform.

Having just bought our Prime earlier in April, my plan is to do this service at 5k miles. I did the wife’s RX450h trans axle drain and fills at 6500 miles and the fluid came out purple.

But no down side and it’s an easy job.

 

I am planning to do mine DIY at 30K when I will do oil and filter change DIY. This will be my first DIY project on PRIME for I had free TOYOTA Care service up to 25K miles.

 

No more so than with any other service - if you do it wrong, you have problems. New fluid is almost always better than old fluid, and if you check for leaks after the job you'll know quickly if you have the plug improperly seated. I used to change out three quarts of ATF fluid in a Honda Civic with every oil change (the trans held about 9 quarts, I think, so each time I put about 1/3 new ATF in for not much money).

Any competent shop can do this fluid change - it doesn't need to be a Prius shop.

 

no downside from what i've read, and plenty of upside based on oil analysis people have done.

many dealers are reluctant simply because toyota calls it lifetime, but they don't warranty it for life.

 

The is the instruction for a gen 4 Prius, don't think the Prime would be any different. A few tips:

1. Have a torque wrench, the drain and fill bolt spec is 37 ft/lb. (Up a bit, 3rd gen was 29).
2. Replace the washers. Dealership should have them. Hopefully the parts department is a bit more receptive. They may need to order them in, if they're never doing the job there.
3. The fill and drain bolts very likely are "socket head cap screw", with a 10mm depression. You can get ratchet sockets in that size. Stanley for one makes a set. Google "hex bit socket set". Considering the 37 ft/lb torque, you do NOT want to attempt this with an allen key. I'd suggest a long handled ratchet wrench for breaking them loose, and a decent quality torque wrench for install.
4. The simplest method to fill is with a funnel with hose extension, snaked down from above in the engine bay. Helps to have an assistant pouring. Go slow as you near the spec'd quantity. Correct level is basically when it starts coming back out. The refill should be done with the car level. Roughly level, you don't have to go nuts.
5. Remove fill bolt first, just in case...
6. Use only Toyota ATF WS. I've read somewhere (can't recall where at the moment), to NOT save left over fluid, that it goes off over time. I have in the past used left over, no problems, but...

There's some weird nonsense in the 4th gen instruction to temporarily reinstall the fill bolt, then remove it when filling. There's no such mention in 3rd gen instruction. Not sure why they say that. Maybe engineers obsessing about leaving it open to the air too long? If you're working fast, not delaying the refill, I don't really see the point of that instruction.

 

Are there even any moving parts in the transaxle besides planetary gears and a differential? Normal automatic transmission cars have wet clutches that are used for every shift, but the power split device/ eCVT never changes gears, it just varies the speed of the motors.

 

There's videos on the internals of the transaxle. I'm not sure why, but I invariably doze off, halfway through these:

 

Besides what you mentioned, I can only think of the parking pawl and the oil pump.

 

One question I have had about the transaxle oil change issue is: yes, after a while, the oil looks crappy and is full of various kinds of gunk. It isn't pretty, but does this actually effect the long-term health of the transaxle? The Prius transaxle has been around about 20 years, so there should be some evidence in this regard.

 

That's really a good question and I don't think anyone knows for sure how much it helps, if at all. But it sure doesn't hurt, assuming you don't screw up something in the process, which can happen with any preventative maintenance. I've done it on all of mine except the Prime that I just got and I plan on doing it before too much longer.

I did it for cheap & easy peace of mind. Even though there have been very few transaxle failures, if it does happen, it'll be downright inconvenient to put it mildly.

 

I think an early transmission fluid change is optimum. I've change ours (3rd gen 2010) more times than I care to divulge, and the first change, around the one year mark and 15K kms, showed the most darkening, compared to the new fluid.

From then on, I would stretch the interval, maybe even just once more, well along.

 

Evidence is where you find it...or buy it.
Coffee has been around for hundreds of years but people still debate whether drinking the stuff is good for you, bad for you, or if it makes any real difference either way.

OK.
So...

As we learned earlier in this thread, it's not really a "transmission" and it's not really "oil."

Since the transaxle (power splitter) is a sealed unit with no air exchange or combustion, I'm not sure what the fluid is being contaminated BY, besides maybe heat.
Also as mentioned above, there are no clutches in the transaxle - BUT(!!) there are gears, and there are electrical windings (motor or stator windings) which tells me that (1) changing the fluid out periodically can be beneficial and (b) you really REALLY need to use the right fluid and perform this maintenance CORRECTLY or you may wind up doing much more harm than good.

Here's my thinking:
MG2 windings are insulated by a thin coating of something that is probably known to the state of California to cause cancer. This insulation "probably" does not like metal shavings, corrosive fluids, or fluids that conduct electricity.
Changing Toyota's OEM fluid WITH Toyota's OEM fluid correctly will probably take care of any potential long-term wear problems, or short term metal contamination but remember.....the power splitter is a sealed unit and there's not much happening in that case except for motors spinning and gears gearing.
Over time.....gears and bearings will wear down, but this is over a LONG period of time and most of the resulting metal bits will be suspended in the fluid and be very very VERY small.



Reader's Digest Version:
Some people change the fluid out regularly, some do it only once or very seldom and some do not do it at all....and since over the last 20 years transaxle problems have not been much of a "Prius thing" I'm thinking that it's not much of a Prius thing.
However (Comma!) the maintenance is very easy to do, and not very expensive so if I found myself owning a Prius, I would change the fluid out at about 30,000 miles and probably about every 60,000 miles thereafter.....but hey.....I also drink coffee.

No.
Not the %^@#!! frappin "cookie-in-a-cup" that millennials drink.

COFFEE.

YMMV.

 

It's surprising that the motor windings are in transmission fluid, not in coolant. But I guess that makes it more compact.

 

The transmission fluid is the coolant.

 

Just like in a large transformer.

 

thanks for linking the PDF

 

Your maintenance PDF states that for fluid replacement 2 flushes should be done before filling transaxle, correct?

 

It's not really a flush, just a fill and drain. I see that it says to do it twice, but I think hardly anyone does that. I never did. In fact, most Prius owners never change the transaxle fluid. I think it's a good precaution to do it once at least. More seems like overkill to me.

 

I’m not seeing this, just a single drain and fill. Seems like some engineer is obsessing about minimizing air exposure, extra, temp install of fill bolt, but that’s all.