When should I change my car's transmission fluid?
The short answer is 'never'... unless your vehicle works hard for a livingThe world has changed and most drivers these days own and operate cars with an automatic transmission. But there are still some cars around fitted with a manual transmission, the old-fashioned gearbox.
Both types of transmission require a lubricant to keep the moving parts inside unit rotating and meshing freely without friction causing premature wear. The lubricant used in gearboxes is much like an engine oil, but heavier in weight and viscosity.
Automatic transmission fluid (ATF) is different again, usually being a mineral oil, or else it can be synthetic – and it is a very sophisticated product indeed.
Not only does ATF lubricate the moving parts within the transmission, including the planetary gears, it also serves as the hydraulic medium for the torque converter, essentially a viscous coupling that serves as the clutch in a traditional (epicyclic) automatic transmission.
Companies producing ATF stir in other compounds that inhibit corrosion, clean metal surfaces, enhance viscosity (further reducing internal parts wear) and prolong the life of the fluid itself.
But as advanced as ATF is, sooner or later it will need to be flushed out of the transmission and replaced with a fresh batch. In constant contact with moving parts its viscosity – its 'body' to hijack a term coined by vignerons – gradually breaks down.
Furthermore, it often becomes inundated with tiny metal filings resulting from long-term abrasion where parts make contact with each other. Neglect the ATF and the transmission will wear prematurely.
The owner's manual for our long-term Hyundai Santa Fe indicates the ATF need not even be checked or serviced for the effective service life of the vehicle (eight years).
However, Hyundai also recommends that in the event that the Santa Fe is frequently and regularly subjected to tough driving conditions, the ATF should be replaced every 100,000km. Vehicles with a manual transmission – a gearbox – should have the oil lubricating the gearbox's internals replaced every 120,000km.
The circumstances that Hyundai foresees warranting transmission fluid replacement are these:
- Repeatedly driving short distances of less than 8km in normal temperatures or less than 16km in freezing temperatures.
- Extensive engine idling or low speed driving for long distances.
- Driving on rough, dusty, muddy, unpaved, gravelled or salt spread roads.
- Driving in areas using salt or other corrosive materials or in very cold weather.
- Driving in heavy dust conditions.
- Driving in heavy traffic areas.
- Driving uphill, downhill, or on mountain roads repeatedly.
- Towing a trailer, or using a camper or roof rack.
- Driving a patrol car, taxi, commercial vehicle or vehicle towing.
- Driving over 170km/h.
- Frequently driving in stop-and-go conditions.
Not all these conditions will be encountered in Australia – autobahn cruising at speeds above 170km/h as an example, or salt on the roads – but many will.
The Hyundai criteria provide a useful guide for owners of all vehicles, not just the Santa Fe owners. Although Hyundai's list doesn't mention it, motor sport competition is another form of extreme driving that compels changing the transmission fluid or gearbox oil sooner than the recommended distance.
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