When to change transmission fluids, etc

[Jared]

I have a 2005 Prius with 65k miles. My mechanic just told me I should replace the automatic transmission fluid and differential fluid. Luckily, I checked my maintenance schedule guide and it says to do this at 60K only if the car is used for towing. Also, how important is it to change the cabin air filter - does it matter? Thanks.

[richard schumacher]

Others will comment on the ATF. As for the cabin air filter: change it or vacuum it if it's dirty. You can easily do this yourself in five minutes. A new one should cost about $21 at the dealer's parts counter.

[Jared]

Thanks, Richard. My maintenance booklet does not mention when to change differential or transmission fluid under normal (non-towing) driving. So when should it be changed?

[richard schumacher]

Uhh, I thought it comes at 100,000 miles? I don't have the maintenance guide at hand.

[mikepaul]

I believe it's 100,000 miles for transmission fluid. Or I sure HOPE that's it because I'm not even looking until then.

I change the air filter every 20,000 miles, needed or not. Cabin filter has been 30,000....

[bwilson4web]

Originally Posted by Jared

I have a 2005 Prius with 65k miles. My mechanic just told me I should replace the automatic transmission fluid and differential fluid. Luckily, I checked my maintenance schedule guide and it says to do this at 60K only if the car is used for towing. Also, how important is it to change the cabin air filter - does it matter? Thanks.

Our testing data suggests the NHW20 in non-dusty environments need to have the transaxle oil changed at ~60k miles. Art's Automotive suggests 30k miles which is OK by me too. In dusty, rural areas, I would go with 30k.

For the older NHW11, I would go with 30k for non-dusty areas and a little as 15k for dusty areas. Again, this is based upon transaxle oil test results. However, it is your vehicle.

If you do have it changed, I would recommend bringing a clean, dry water bottle, about 1 cup, and have a sample taken. If it smells burnt or shows a very dark color, you may want to have it tested to see how badly it was worn. About 15% of the old oil remains in the transmission after a change so this may shorten the time you go before another change.

Testing needs to cover 40C and 100C viscosity and the viscosity index. This is your primary wear indicator. The secondary wear materials and particulate counts are useful but not nearly as much as the two temperature viscosity measurements.

Bob Wilson

[Patrick Wong]

Originally Posted by Jared

I have a 2005 Prius with 65k miles. My mechanic just told me I should replace the automatic transmission fluid and differential fluid. Luckily, I checked my maintenance schedule guide and it says to do this at 60K only if the car is used for towing. Also, how important is it to change the cabin air filter - does it matter? Thanks.

Hi Jared,

I agree with Bob that periodic transaxle fluid changes are appropriate to help extend the service life of this very expensive part. I change the fluid on my 2004 at 30K mile intervals.

Note that "differential" and "automatic transmission" are one and the same as far as Prius is concerned. The 2G transaxle requires 4 qts of Toyota ATF WS fluid.

Regarding the cabin air filter, since you are breathing the air that passes through the filter you might be motivated to change it from time to time. I suggest that you remove it and see how dirty it is. If it hasn't been changed over the last 20K miles or more, it will probably have a disgusting amount of debris on it.

[Jared]

Thanks for the advice. But I have some questions.

1. The printed Prius scheduled maintenance guide that came with the car states on page 11 to replace the automatic transmission fluid and differential oil (2 separate entries) at 60k miles only if towing. On page 3 it says about "special operating conditions"

"You should perform these additional maintenance services if you drive primarily under any of the special operating conditions indicated. If you drive only occasionally under these conditions it is not necessary to perform the additional services"

So according to Toyota's own maintenance guide, I should not change the transmission fluid or differential oil. I think it is best to do what the guide says, no more and no less.

[Patrick Wong]

Originally Posted by Jared

So according to Toyota's own maintenance guide, I should not change the transmission fluid or differential oil. I think it is best to do what the guide says, no more and no less.

That's your decision. However note that for marketing reasons Toyota might suggest the minimum necessary maintenance so that the car will reach 100K miles without undue mechanical problems. If you are interested in having your car last longer than 100K miles, then you may choose to have more service performed than the bare minimum. A transaxle fluid change will not hurt the car, and may help its ultimate longevity...

In my case a transaxle fluid change costs me $20 for the fluid, $2 for the drain and fill plug washers, plus 1/2 hour of my time - so this is not a big investment. If your mechanic wants $100 for the service I can see why you might think twice.

[Jared]

Well, I have always followed the owner's maintenance guide to my 1995 Tercel to the letter and it has reached 180k with no problems. I think if Toyota says something is unnecessary, it probably is unnecessary. But it is interesting that the manual list automatic transmission fluid and differential fluid as separate things.