Is it advisable to change the fluid in my transmission at 80-85k miles? Is there a procedure to properly do so? I heard it's about 4qts.

 

Transmission oil drain and refill frequency depends on if car is used in severe conditions such as stop and go city driving, towing, sub-zero temperatures, high ambient temperature, frequent awd use on ice, high speed driving and if car has an external transmission cooler which was included as part of the tow package on some models, 3RX F-sport has an external transmission cooler as standard. I like a yearly drain and refill at local Toyota dealership which gets the right WS fluid and temperature corrected amount, cost was $100 last time I put car through, we've serviced a Scion tC and older 4runner the same for several years with good result.

 

What year is your RX? Is it a 350 or 450h? If a 350 the following applies. The hybrid is different and easier to do.

Yes I would change the fluid. A few years ago I bought a used 2013 Toyota Sienna with 89,000 miles and it has the same transmission and engine as the RX. I think it had the original ATF. and found the fluid level was 1/2 quart low.
I did 4 cold drain and fill transmission fluid changes. They were spaced a couple of weeks apart. The transmission operated perfectly when, 18 months and 30,000 miles later I traded it in for a low mileage 2016 Seinna Limited AWD.

If you know how to do an engine oil change, then you can do a cold drain and fill on this transmission. If not, take it to a Toyota shop or transmission shop that knows how to do a drain and fill.

Be sure to only use either Toyota WS ATF or Idemitsu TLS-LV ATF, which you can buy 5 quart jugs of at NAPA, Amazon etc. Here is a link to the merged thread on changing the ATF.
https://www.clublexus.com/forums/rx-...d-threads.html

I will quickly describe the simple cold drain and fill method. They key to success is to have the vehicle off for at least 6 hours before doing this so it and the new fluid are the same temperature as the fluid expands when hot. You need to measure exactly how much you drained (about 2.2 quarts) and replace that exact amount plus a few extra ounces for spillage.

The drain plug takes a 6mm Allen wrench. Once removed about a quart drains. Then stick the Allen wrench inside the drain hole to remove the plastic overflow tube. Another 1.5 quarts or so will drain. When reinstalling the overflow tube just lightly screw it in until it stops moving. No need to tighten as the drain plug holds it in place and you do not want to break it.
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Use a measurement market bucket such as is sold in paint stores or departments to measure the fluid. Or fill a couple of empty quart oil bottles. I think 2.2 quarts is the proper amount aftering doing this for 12 years. So if you drain less, you may be surprised at the improved throttle response with a little more fluid.

The fill hole is a 24mm bolt on the side that you have to access through the driver side front wheel well. REmove the tire, and find the small flap on the left side that is held on with a bolt and some plastic things. The bolt is behind it. All you need is a long funnel to fill it up.

 

Wife's 2010 RX350 had 106k miles on it when purchased last year. Transmission was working perfectly but since Lexus never serviced the transmission we had it done soon after purchase at a non-dealer specializing in Lexus. They hooked up a machine that replaced all transmission fluid (bill showed 6.6qts). Transmissions works perfectly.

After reading so many cautions here and recommendation to only change a little transmission fluid at a time... I asked the head service guy about it. He chuckled and said he gets asked that question all the time. Told me of the thousands of transmissions they've serviced the only problems were with transmissions that were already having problems. I believe him. Glad it's one and done. Only around $100.

 

I agree.

A properly performed fluid flush on a transmission that is operating correctly generally will not cause any issues anymore so than a drain and fill service.

The issue with flushing a transmission tend to be on ones that were neglected and was already slipping before the flush or in which the flush was performed incorrectly by a shop that used the incorrect fluid or improper fluid level.

 

Here's another professional opinion of when and how to change oil in Toyota transmissions;

 

Keep in mind 3rd gen has the 350 and its sister 450H.

They have different transmissions and amount of replacement fluid is different. For 450H you need 4 qts for drain and fill [no torque converter and drain gets 95% est. fluid out].

Salim