The truth about servicing automatic transmissions (even the sealed ones)

All automatic transmissions need regular servicing. Even the ones the carmakers say are ‘sealed for life’. Here’s the ‘when’, and ‘why’ that might just save you tens of thousands of dollars in transmission repair bills

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Executive summary:

Heat kills transmissions by destroying the fundamental protective properties of auto transmission fluid (the ability to maintain a tough, thin film separating the precision metal parts).

For every 15 degrees C operating temperature above 80 degrees C, operating life of the fluid is halved. (Hypothetically, ATF at 80 degrees C might last as long as 160,000km.) So, at 95 degrees, life drops to 80,000km. At 110, 40,000, etc.

Above 110 degrees C - all bets are off, basically.

Get a decent Bluetooth OBDII dongle and measure your transmission operating temperature, if you subject your vehicle to severe operation. (Such as towing a big caravan or boat at highway speeds in summer, etc.) This will tell you definitively whether your transmission is overheating or not.

Follow the manufacturer’s instructions about heavy towing (owner’s manual). Procedures might include turning overdrive off, or driving at a reduced maximum speed.

In the absence of a manufacturer-specified servicing frequency, I recommend something in the ballpark of 60,000km or three years for a transmission service with fluid change. If the vehicle is subjected to severe operating conditions (heavy towing, etc.) change that to every 30,000km (especially if the fluid gets over 100 degrees C).

Routine transmission servicing is dirt cheap, in comparison with a complete overhaul or replacement in the event os a catastrophic failure at the roadside.

This video report is in response to the following question from a viewer named Barry, and I really think a lot of people are in this position:

I really enjoy your videos as they give us non experts factual information that's difficult to get from other sources that are often less reliable.

I'd like to get some facts from you about what are harmful temperatures of the oil in automatic transmissions. I drive a 2.8-litre Prado with auto transmission and I occasionally tow a camper trailer weighing 1.6 tonnes. Connected to the OBD2 port in the Prado is a ScanGauge2 that allows me to see the readings from many of the sensors on the car. I've been particularly interested in the readout of the transmission temperature.

Some time ago you published a video that recommended using auto setting to tow & not to use the transmission as a "manual". Normally when towing I'd set the transmission into the 1:1 ratio 4th gear & tow in that mode. After watching your video, on the next camping trip to western Queensland I put the Prado into ‘D’ to see what, if any, difference it made. It did drive a little differently (shifted gears a lot more as it moved between the 5th & 6th overdrive gears to 4th gear or lower depending on the terrain).

The transmission temperature in this auto mode was regularly in the range of high 90 to over 100 deg C with the ambient temperature in the mid to high 20s.

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Next I went back to my default towing mode with the transmission set to 4th as the highest gear ratio used. There were less gear changes (no surprises there) but the transmission temperatures were definitely lower, mostly in the 80s and occasionally into the low 90s. Ambient temperatures were the same as before. The downside was that the fuel consumption was slightly higher. At a service after that trip I got my mechanic to change the transmission oil as on inspection it appeared much darker than normal. I'm not sure whether this was a result of the way it was driven on this trip or not.

My understanding is that the optimum temperature for longevity of an auto transmission is somewhere in the 80 deg range & anything higher was likely to cause long term damage if the oil wasn't changed regularly (the Prado service schedule is for an oil change each 40,000 kms or 2 yrs). Can you give me some guidance on whether this is correct or not & what regularly running at the types of temperatures seen in auto mode are damaging. There must be many Prados (and other makes) out there that are used for towing and driven in a ‘set & forget’ fashion that could be just waiting for an expensive appointment with a service centre.

I'd appreciate your comments on this subject.

Many thanks,
Barry

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