To change or not to change the ws atf early?

As Prius owners, our interests and Toyota's interests do not totally align. We may be interested in keeping the car for a very long time, well beyond industry end of life standards of 10 years/150K miles. Toyota needs their cars to last "long enough" to not disappoint their owners, but obviously they need owners to periodically purchase a new vehicle.

Regarding your question, my guess is that this is for marketing reasons: one less item on the maintenance schedule. As long as the transaxle will last 100K miles without an ATF change, no worries.

The reason that some PC members (including me) have advocated periodic transaxle fluid changes is because the Classic transaxle had a number of failures and used ATF testing revealed very high Si, Cu and Fe content. Hence, the thought developed that it would not hurt and might help the transaxle to change ATF periodically.

If you are happy to have your transaxle full of tiny metal and dirt particles and think that will improve it's longevity, then no worries. Why not grind up more iron and copper bits then, and add to the fill hole.

 

Metal particles, in the percentages that are in the old, used ATF, do not contribute materially to the heat transfer characteristics. The amounts are too small. For real heat transfer with metal flow, one needs something like the molten Sodium that is used in nuclear reactor heat exchangers.

In any case, the majority of the metal particles in our transaxles are sequestered at the magnetic plug, and not flowing about inside. The electrical conductivity concern, with regards to the MG windings, is also not a factor, as the conformal coating on the windings is what protects the system. If there is a fault in the coatings, then it's game over sooner or later, no matter what is the state of the ATF.

I changed mine at 35,000 miles, and was glad to get new stuff in there. Temperatures were close to the same after that, with maybe a small reduction in MG1 temp. Toyota allows the winding temps to get over 100C before a DTC is set, which is fantastically hot to my mind. I see 70C for MG2 when on slow, hilly terrain during hot weather.

 

Toyota no doubt balances a few variables to determine oil change intervals and I would expect utilise oil sampling when testing to ensure the wear is minimised. The only reason I have heard for not changing oil early is due to the introduction of contaminants during the oil change process but most would agree that if done correctly this would be almost negligible if not zero in my opinion.

Cheers,

Gavin
www.currenttech.com.au

 

Epoch, if you really believe that, then don't change the transmission oil.

 

I appreciate that Epoch is only putting forward a theory. However this theory is self defeating by the recommendation to change the fluid at all. If the fluid was changed at 100,000 miles any positive reason for leaving it in till this mileage is discounted by asking for it to be changed.

John (Britprius)

 

That logic also says that changing engine oil is dangerous as well (It may be at a quick-oil-change establishment).

JeffD

 

I have yet to hear of a coolant or lubricant that was engineered to become contaminated (or even where unintended contamination is desirable). No offense, epoch, but your theory is total hogwash.

 

Not wishing to get into an argument here but engine oil is partly designed to do just that, but then stopping the contamination from doing any damage.

John (Britprius)

 

I stand corrected. You learn something new every day.

 

Wow. Obvious troll is...obvious. That's like saying marriage is the sole cause of divorce.

Having said that, I like Epoch's philosophy and wish to subscribe to his newsletter. He has a great career ahead of him as a Toyota dealer service tech...the kind that torque 76 ft.lb. wheel nuts to 110+.