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Transmission fluid flush on Pruis

Do I need to flush to transmission fluid on an '05 Prius? Some people (dealer) say yes, others (Badger Transmission) say no. The No’s argue that it’s a closed system and that maintenance isn’t necessary.

What does your owner’s manual say? It’s a very specific system on the Prius, I’d follow the manual’s recommendation to the letter.

If you have a dipstick for the transmission, then you can check the color of the fluid. If you have the newer 5 speed automatic, then you probably don’t have a dipstick and it is a closed loop system meant to last the life of the vehicle.

Now the dealer may or may not be giving you good advice, but he does have a vested interest here. Toyota considered the transmission fluid in their 4 speed automatics as a lifetime fluid, but many owners found out that that wasn’t necessarily true. My daughter’s 03 Corolla’s transmission fluid turned black at about 75k miles, so I changed it, twice.

The newer transmission needs a special machine in order to drain and refill the transmission. It can’t be done without this machine. The dealer had to buy this machine and now would probably like to get his money back by selling this service. It is possible that through customer experiences that he has reason and evidence to believe that you really do need this service.

You might google for a prius forum to see if anyone there has any recommendations.

The Prius’ transmission is specially integrated with the IC engine and the 2 electric motor/generators. It uses a planetary gearbox (not a normal automatic, nor a belt-based CVT) to connect the three to the front wheels. Here’s a good explanation of how it all works, plus a good animation:

I would imagine that the only thing special about the oil in the Prius transmission is that the motor/generator windings are submerged in the oil. The oil cools the windings.
So, the oil has to be dry like transformer oil for maximum motor/generator insulation life. Other than that, it’s just gear lube I guess.

I am not at all comfortable with anything claimed to be a “lifetime” fluid.

Your oil is also lifetime, of course. If you never change it, it will be good for the lifetime of the car - which just happens to be when the old oil kills it.

That said, I don’t know anything about the Prius drive train (other than the obvious hybrid characteristic). I would put in a call to Toyota corporate. I would also call a couple of other transmission shops - see if there seems to be any dominant judgment about it.

Well if you look at a vehicle, there are many closed loop systems. The transmission, the cooling system, the power steering system, the oiling system, and even the AC system.

If the fluids are either lost or break down, the system breaks down.

Closed loop doesn’t mean it lasts forever.


I think there is some confusion here. In the case of some Toyota transmissions and now the new Chrysler transmissions, there is no dipstick and no place to add fluid. You cannot do a drain and refill like we are used to. If the fluid has to be changed, it is done on a special machine. They took away our access to maintain our own cars transmission fluid. It has to go to the dealer for service.

You’ll get the best advice at

You will get the BEST advise in the maintenance guide published for that car…It might be in the owners manual or it might be a separate publication, but it exists…

Since this component is critical, (if it blows, the car is probably totaled) I would get the FACTS on the service requirement…

Normally the vehicle’s service guide is the place to look - but in the case of transmissions its obvious that the official manufacturer’s service schedule is just plain ridiculous.

More and more car companies are using “lifetime” fluid and do not recommend any change interval at all for their transmissions. When the tranny fails, it’s considered the lifetime of the tranny.

The best source of information is the owner’s manual. But if it says not to change the fluid, I’d disregard that. I’d talk with transmission shops and research online.

I believe in a regular fluid and filter change every 30,000 miles. If the only way to change the fluid is a complete exchange, that interval is probably excessive. If I couldn’t find good answers and had to wing it, I’d probably get the fluid exchanged every 60,000 miles. That might be too frequent, but I’d err that way before hoping the fluid lasts longer. If the car lasts 300,000 miles, that’s only 4 times (you wouldn’t change the fluid at the end of the car’s life).