How to change auto transmission oil

Automatic transmission fluid is one of the least thought of items for vehicle maintenance.

This article was originally published in the June 2013 issue of 4X4 Australia.

Even though some manufacturers do schedule a fluid change every 40,000 to 60,000km or so, plenty of others claim that the transmission is ‘sealed for life’. A very short life, I say. Transmission fluid is there to catch the impurities and clutch material as it wears and it’s no good for any transmission to have dirty fluid circulating through it. It should be changed regularly.

This story is meant as a general guide only; you will need your vehicle’s workshop manual, a socket set, an oil drain pan and some mechanical aptitude. You will also need a new transmission filter, either a cork gasket or high-temp silastic and the correct transmission fluid type and quantity.

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First thing to do is take your vehicle for a drive to warm up the transmission. Then park the vehicle, with the handbrake on and the transmission in Park. Make sure that you have parked on level ground and that the wheels are chocked. Do the job on a calm, still day to avoid debris blowing into your transmission when it’s exposed.

Pull out the dipstick first and set it aside. Then get under the vehicle with your socket set and drain pan. If there is a drain plug, unbolt it with the pan ready to catch the oil. Be careful when you pull out the plug not to burn yourself as the oil will be hot – gloves are a good idea. Some vehicles do not have a transmission drain plug so you have to unbolt the pan and let the oil drain.

Remove the bolts holding the pan in place except for a couple at one end; leave these threaded-in loose and prise away the opposite end of the pan from the transmission housing.

Oil should start pouring out of the side of the transmission pan, so get ready to catch it with the oil drain pan. When the oil coming out is down to a drip, slowly release the remaining bolts and remove the pan, allowing the remaining oil to drain before doing so. Then you either pull down the transmission filter or unbolt it from its fitting position, discard and bolt up, or push into position, a new filter.

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The mating surfaces for the transmission pan and housing must be cleaned so that no old seal remains. Don’t use a metal scraper as it’ll damage the surface and possibly make it difficult to seal up later.

Most transmission pans have magnets attached to them to catch any metallic fragments circulating in the transmission and you should make sure you clean these well before replacing them on the pan.

Some transmissions are sealed with a cork seal while others use a silastic gasket. We chose the latter for this Jeep. With the gasket in place fit the transmission pan to the housing and bolt up loosely. Then tighten the bolts to the specified torque, ensuring you spread the load equally on the gasket by tightening bolts around the pan on opposing sides.

Changing Auto Transmission Fluid - Step-by-step

1. Remove the auto transmission dipstick and set it aside.

2. If fitted, unbolt the drain plug and let transmission fluid drain into oil tray.

3. Remove transmission retaining bolts around the periphery of the transmission pan.

4. Leave a few bolts in loose at one end and let the remaining fluid drain out.

5. The transmission pan removed and the transmission filter exposed.

6. Some filters can be twisted off but this one has to be unbolted before removal.

7. Clean up the pan and scrape off old gasket from the pan and transmission housing.

8. Most pans have magnets like this that will need to be removed and cleaned.

9. Fit the new transmission filter and bolt it into place.

10. Apply a new bead of gasket sealer to the transmission pan then put gasket on.

11. After bolting up the pan, fill transmission with correct amount and type of fluid.