Transmission Fluid flush frequency

Modern transmissions are designed to have “fill-for-life” fluids, however transmission experts recommend transaxle/transmission fluid be flushed/changed periodically to prolong working life of the transmission.

Traditionally, the transmission is FLUSHED every 30,000 miles [48,000 km] or every 2 years (24 months) whichever comes first.

Automatic transmission fluid should be CHANGED every 10,000 miles [16,000 km] or every 8 months whichever comes first.

Replacing the transmission fluid is recommended because of these reasons:
- driving in the city (frequent stop-and-go)
- hauling heavy loads
- trailer towing
- snow plowing

The above reasons will cause the transmission fluid to overheat and deteriorate faster.

Overheating causes breakdown of the transmission fluid which in turn causes transmission failure. This is indicated by a dark or cherry red color of the fluid and bubbles appearing on dipstick, meaning that its viscosity started to wear down as well as fluid showing signs of deterioration.

This will eventually cause the friction clutch plates inside the transmission gearbox to fail their frictional holding ability and start to slip. Once the slipping happens, the transmission fluid will become hot.  This will lead to failure in shifting gear. The radiator or cooler is not sufficient to cool down this overheating problem.

It costs around $100 to $200 for a transmission flush.

It costs around $3,000 to $5,000 to rebuild a transmission.  Do the recommended maintenance routine to avoid getting to this point.


*** 2008 KIA SPORTAGE ***

For example purposes, according to the 2008 KIA SPORTAGE owners manual, these are the recommended fluids:

1.  Engine oil --> API Service SJ, SL or above; ILSAC GF-3 or above  [SAE 5W-20, 5W-30 for temperatures -30 to 50 C (-10 to 120 F)]

2.  Automatic transaxle fluid --> DIAMOND ATF SP-III or SK ATF SP-III  [Replace every 32,000 km or 16 months]

3.  Power steering fluid --> PSF-III

4.  Brake/Clutch fluid --> FMVSS116 DOT-3 or DOT-4

5.  Coolant --> Ethylene glycol base for aluminum radiator

6.  Fuel --> Unleaded gasoline with AKI 87 or higher



THEORY:   "LEAVE THE TRANNY ALONE", IF IT'S WORKING FINE"

The problems with flushing can be:
1. Introduction of foreign particles, grit, or dirt when backflushing, draining and changing the filter.
2. Replacement of ATF fluid that is not compatible with factory fluid, thereby losing fluid friction properties (for holding clutches).
3. The clutches in the AT will wear in the passage of time and wear particles actually help keep the transmission from slipping as it ages.
4. When you flush, the tranny loses those wear particles and thus cause slipping.