The "RX 300 How2" web site

RX 300
Transmission Fluid
Change [difficulty level 3]

What the service manual states:

The Automatic Transaxle or transmission uses 4.3 quarts (4.1 L) of Type T-IV Automatic Transmission Fluid (ATF) for in the AWD model.

Change the ATF if you operate in special conditions (towing, dusty, salty, short trips, commercial use, etc.).

Nothing about "hard driving"...hummm? No mention of changing the fluid on a regular basis... In other words, you never need to change the ATF if you drive normally?

For years, manufacturers have attempted to enhance their selling efforts by claiming their vehicles are low maintenance. That is, they don't require a lot of work when brought in for service. They point to the vehicle's service manual. So the RX manual implies you never need to change the transmission fluid if you "drive normally".

I prefer to follow a more liberal maintenance schedule and change the ATF at "major service" intervals (30,000 miles), which is the time Lexus first mentions the transmission fluid should be checked in their "special conditions" section.

Most auto manufacturers have a similar guideline - you don't need to change it. I like to change everything, just for peace of mind and mostly to inspect and evaluate the maintenance condition of the vehicle. Of course dirty contaminated oil does not help the longevity of a transmission!

I have not been able to purchase Type T-IV ATF anywhere locally except at Lexus or Toyota parts departments (about $5 US/qt) at the dealerships. You may be able to find it on-line.

The transmission oil dip stick is in-between the battery and the engine - orange top. Checking the level can be done when hot or cold because there are 2 sets of marks on the stick.

Below is the fluid specifications from the manual:

The drawing to the right is from the Toyota manual with a few labels added.

Ok, the transmission (AUTOMATIC TRANSAXLE) holds the T-IV fluid (see above table), but what is this TRANSFER case thing?

The transmission output is coupled to the wheels through a transfer case/unit (bolted to and just behind the transmission).

I drained out 3 quarts of fluid from my 1999 AWD transmission. What happened to the rest of the 4.1 quarts? The dipstick had indicated a normal level in the transmission before I started!

I actually expected to drain out less because in automatic transmissions the Torque Converter (fluid clutch) may hold a bit of the fluid that will not drain out when draining from the bottom plug. Also, the transmission oil cooler and lines will hold a portion of the ATF.

For the average home mechanic (and many other "professional mechanics") the approach to changing transmission fluid is to avoid extra work (time) or special equipment and do the lease expensive, least time consuming procedure. In this case, the short cut to change most of the fluid is acceptable.

[Yes, I know the undercarriage is dirty. Up here in the northeast, salt is a constant winter problem. I hate it!]

I drained the 3 quarts (approximately 75% of the total capacity) and refilled the transmission with fresh T-IV. So, I've changed most of the oil. After doing this 2 or 3 times, you have essentially "changed all the oil."

The schedule I use is to change the transmission oil with every engine oil change for the next 2-3 crank case oil changes. This is sufficient for my vehicles and I would do this sequence every 30,000 miles or so (major services).

The way I start is to jack up the front end a few inches, enough to get the drain pan under and room to work. Then insert jack stands for safety.

The drain plug is loosened with a hex wrench or hex socket (10mm). I have my drain pan ready, plenty of newspaper on the floor and rags handy for my hands.

Once loose, I unscrew the plug by hand over the drain pan and try not to drop the plug! When replacing the plug, it is not necessary to over-tighten the plug, there is no pressure inside the oil pan.

I always inspect the inside of the plug, there will be a small amount of dirt collected in the recess. The plug gets cleaned before replacing.

If one were to remove the oil pan, one would find a couple of small magnets in the bottom of the pan that collect any steel chips or fillings from gears and clutches. A small amount is normal. Brass collected in the bottom of the pan would be from bushings.

After draining, I replace the plug and lower the vehicle. Dispose of the old oil properly. Drain Plug torque: 49 N-m, 500 kgf-cm, 36 ft-lbf

A funnel with a very narrow neck (tube) to sit in the dip stick filler tube is used. I have this old funnel I keep just for this purpose.

This is the fun part!

Nice fresh fluid - it sort of looks like the cherry cough syrup my mother gave me by spoon when I was a kid. Sort of a brilliant red - almost glowing in the florescent work light.

I pour in the 3 quarts removed. I start with 2 quarts and check the ATF level. I make sure the vehicle is on a flat level surface for proper readings. Then I add maybe another 1/2 qt. and check again. Keep pouring and checking to just get into the "COOL" marks on the stick.

Once I have the level correct, the engine is run at idle and the transmission warmed.

While at idle and stand still (foot on break), I shift through the gears and back to park. After warming, I let the engine idle and check the level to make sure the fluid is near the hot marks. Then I'll drive the vehicle to get the fluid into the HOT range and check the level once more to make sure the level is between the "HOT" marks, toping off the fluid if it is a bit low.

Completing this job is very satisfying.

Here is what the Lexus shop manual says
about replacing ATF:
- Remove the drain plug and drain.
- Reinstall the drain plug securely.
- With the engine OFF add new ATF Type T-IV.
- Start the engine, let idle and with your foot on the break shift the shift lever into all positions from P to L and then shift into P position.
- With the engine idling in P, check the fluid level. Add fluid up to the COOL level on the dipstick. Only use the COOL range on the dipstick as a rough reference when the fluid is replaced and is not yet hot.
- Check the fluid at normal operating temperature (warm up the engine to the usual hot temp on the dashboard temp gauge). This is 70-80 deg C (158-176 deg F), and add fluid as necessary.