Too Much ATF in Automatic Transmissions: Causes and Potential Risks

It is not a secret that the operability of modern automatic transmissions heavily depends on ATF (automatic transmission fluid), or more precisely on its condition, level, and temperature. Most of automatic transmission issues stem from ATF, thus repair professionals pay special attention to ATF and its timely change. If potential risks of lower ATF level are intuitively clear to most of car owners (oil starvation can lead to numerous malfunctions or even failure of the whole transmission unit), the situation with the fluid overflow may be misleading.

Some inexperienced car enthusiasts mistakenly believe that if the low ATF level can be extremely harmful for the transmission, then it is better to fill as much lubricant in the automatic transmission as possible. But it is a serious misconception. In this article, we will discuss negative consequences of ATF overflows for automatic transmissions and how to solve this problem.

How it happens?

When performing regular maintenance procedures, which necessarily include the ATF level check, you may unexpectedly find out that the ATF level is somehow above the norm. As a rule, this situation frequently occurs after adding the fluid filling-up or its complete change. Less often, this issue can be caused by some malfunctions in the transmission unit. It should be noted that it would be a mistake to measure the ATF level without the transmission warm-up.

Consequences of ATF overflow

In some automatic transmissions, too much ATF can lead to instant transmission faults that manifest themselves in jolts, kicks or error codes, while in some cases transmissions can continue operating without any symptoms of the existing problem. Anyway, it is important to understand that the ATF level must be kept normal, avoiding its scarcity or excessiveness, even if the transmission operates normally. The thing is that ATF, in addition to its main functions (lubrication, protection, cleaning and heat removal), also plays the role of a working element of the transmission. The process of torque transfer in the torque converter is implemented by means of the transmission fluid. Moreover, ATF is a key element in the valve body operation, as its circulation via valve body channels ensures automatic gear shifting.

Now let us pay more attention to actual consequences of the transmission fluid overflow. First of all, in the process of operation, ATF heats up heavily and its volume increases as well. If there is too much fluid in the transmission, then it usually starts foaming, causing leakages in gaskets and seals. Thus, we can say that overflows can lead to potential faults in air-tightness and emergence of leakages. Moreover, ATF can leak through the dipstick.

Learn more about the symptoms of ATF overflow and possible solutions

If leakages are unpleasant, but not critical, then other “hidden” consequences of the fluid overflow can bring much more harm. For instance, the pressure of the foamed fluid is not enough for proper operation, as it leads to deterioration of lubricating qualities and slippages of friction elements. Bubbles noticed on the dipstick during the ATF level check, can become an additional symptom of the fluid overflow and its foaming. Excessive fluid also can reach seals and damage them.

As a rule, fluid overflows manifest themselves in kicks and jolts in the automatic transmission during shifts, consequently leading to wear of transmission parts and poor cooling of the transmission unit. In this case, it is necessary to check the fluid level after the transmission warm-up. If the fluid level is too high, it should be adjusted.

How to drain excessive fluid

There are several ways to remove excess oil from an automatic transmission. Many transmission specialists use a special fluid syringe. It is just necessary to put a thin rubber tube on the syringe and then insert this into the dipstick hole and pump out excessive fluid.

If you have to deal with so-called maintenance-free transmission that does not have a dipstick, then it is possible to drain excessive fluid after removing the external oil filter. It is also possible to disconnect hoses from the radiator cooling system or unscrew the drain plug. It is also important to remove the excessive fluid by parts, constantly checking the fluid level during the process.

Useful tips

Before checking the fluid level, it is necessary to warm-up your car properly. For this purpose, it is necessary to drive your car for at least 10 km. Then the car should operate at idle speed for about 5 minutes, after that it is necessary to shift through all gears with the help of the shift selector, lingering at each gear for 2-3 seconds. Do not shut off the engine and leave the selector in P mode. After that, you can get out of the car, remove the transmission fluid dipstick, wipe it with a clean rag and insert it back firmly for 2-3 seconds. Then the dipstick can be removed once again and check the fluid level.

When examining the dipstick, do not forget that the normal fluid level must be between marks HOT and COLD. A shift towards HOT by 2-3 mm is allowed, but not higher. In some cars, there is only one mark and in such cases this mark should be used as an orienting point. For some cars (especially models equipped with so-called maintenance-free transmission without a dipstick), specialists recommend filling in the same amount of fluid as has been previously drained. When changing ATF, do not forget to use the fluid that is recommended by the manufacturer of the car or transmission unit itself. If you decide to use an alternative ATF variant, then make sure that it complies with all tolerances and recommendations specified by the manufacturer in the manual.

All in all, it can be concluded that it is extremely important to avoid both the low fluid level as well as its overflows. To avoid serious trouble with the transmission, it is necessary to devote considerable time to examining the car manual and learning peculiarities of ATF change.