Myth about lifetime transmission fills
There has been a lot of talk lately about “lifetime” transmission fills, so in this post I will take a closer look at this issue.
Lifetime transmission fills have destroyed thousands of transmissions all over the world, simply because transmission fluid breaks down, just like any other lubricant. More importantly though, a new transmission has a lot of relatively rough wearing surfaces, which means that the metal particles that wear off internal components eventually end up in the fluid, where they are filtered out by the transmission filter.
However, many “lifetime” transmissions do not have internal filters any more. Instead, they have fine metal mesh strainers or screens, and the problem with that is the fact that most metal wear particles are small enough to pass straight though the strainer where they can become stuck in the valve body, where they can cause hard and/or erratic shifting, or sometimes a failure to shift at all because they prevent valve shuttles in the valve body from moving freely.
That is just one of the many problems with lifetime fills. Another issue is that since many transmissions do not have proper filters, metal wear particles are allowed to circulate freely, despite the fact that almost all transmissions have two more magnets in the oil pan to “capture” floating metal particles. In practice though, there is no guarantee that any magnet will always capture all metal particles, so in effect, the metal in the fluid turns the fluid into a sort of grinding paste that causes premature wear on the clutch packs, bearings, planetary gears, and small moving parts in the valve body.
Then there is the problem of additives in the fluid that break down. Many car manufacturers claim that the fluid in their lifetime fills is fully synthetic. That may be true in some cases, but they are only telling you half of the story. The fact is that the word “synthetic” means nothing in itself, since even the best synthetic fluids do not offer enough lubrication on their own.
All synthetic lubricants need additives like friction modifiers, anti-foaming agents, and corrosion inhibitors to protect against corrosion and mechanical wear, and there is no single additive that lasts forever. ALL additives break down over time due to the effects of heat, moisture and contact with oxygen, and while this breakdown process takes longer to occur in transmissions than in engines, it does happen, and when it does, it causes problems with shifting because the fluid no longer lubricates the transmission properly.
One of the major manufacturers of transmissions, ZF, recommends that the fluid in their products be replaced every 80,000 kms, but car manufacturers have made it almost impossible to replace the fluid. It is certainly possible to replace the fluid when you start experience shifting problems, but the problem is that nobody knows how much fluid most modern transmissions take.
Measuring the amount that comes out of a transmission when you remove the oil pan is only a part of the fluid charge- the rest remains behind in the torque converter and in the valve body, so you don’t know how much fluid to put back in.
Overfilling a transmission is just as bad as under filling it, which means that unless you have diagnostic equipment with the correct software to measure the temperature of the fluid as you fill the transmission, you could accidentally destroy the transmission by overfilling it. Transmission fluid expands as it heats up, which means that a transmission must be charged with the correct amount of fluid, with the temperature of the fluid determining the exact volume of fluid required.
In most cases, this temperature is about 400C, but unless you can measure this temperature accurately, you could end up over filling the transmission as easily as under filling it. A modern car transmission can take anything between 4.5 and 6 litres of fluid, but since you don’t have a dipstick to gauge the level with, you just don’t know how much, or how little fluid to put in the transmission.
So is a lifetime transmission fill a bad thing? It is absolutely a bad thing because you cannot service such a transmission, and there is a good chance that the dealers don’t know how to service a malfunctioning transmission with a lifetime fill as well. Moreover, you don’t get a lifetime guarantee to go along with the lifetime fill, so you are basically on your own when the transmission fails if the car is not covered by a warranty- and that is a very bad thing indeed.
Bottom line, change the transmission oil and filter every 50,000 to 60,000 kms irrespective of the car manufacturer or dealer advise of lifetime transmission fills. This is my personal advice based on burning my fingers twice by believing in the theory of lifetime transmission fills. Both the time all my internet research and consultation with top mechanics taught me this lesson.
