Transmission Fluid – What If You Put Too Much?

too much transmission fluid

Understanding the right usage of transmission fluid can’t be ignored. Paying no attention to it may result to expensive repairs, transmission replacements, or worst, the junking of the malfunctioning vehicle. A common error drivers commit is overfilling or putting too much transmission fluid.  

What is transmission fluid for? 

Transmission fluid plays the role of a lubricant. It is the substance used to make car engines run smoothly. Specifically, it targets the transmission whose parts create friction as they move during the operation of the car.

While lubrication is the main purpose for using transmission fluid, it also has other functions:

  • It conditions gaskets.
  • It protects metal surfaces from wear.
  • It helps control temperature.
  • It helps increase rotational speed.

Symptoms of an overfilled transmission

There are three symptoms to check out for:

  • Formation of a puddle of the fluid under the transmission - check for leakage on the transmission’s seals.
  • Failure to properly shift – caused by foamy fluid.
  • Overheating – due to failure to negate friction.

Consequences of overfilling

Some of the things that can happen to a transmission that’s overfilled include:

  • Increase in temperature
  • Reduced lubrication and cooling
  • Jerky, erratic shifting
  • Fluid overflowing (for certain engine designs)
  • Seal damage
  • Oil starvation

From Foaming to Irreparable Damage

In a normal setting, a large amount of the fluid goes to areas with fixed volumes; the rest of it goes to the pan that’s located below the rotating shafts. That’s comparable to engine oil. Much of it stays at the bottom of the engine under the rotating crankshaft.

You know what it means to sprint in water – it will decelerate you! Those shafts are not going to spin easily if drenched in fluid or oil.

Above the fluid is gas or air. The spinning shafts will then cause fluid and air to mix, forming foam. Foam will then be thrust into the hydraulic system, but since foam hardly flows as smoothly as oil, proper lubrication and cooling will not be possible.

Severe damage can happen next. If you’re talking about an automatic transmission, foam will implode when compressed in the hydraulics. On the other hand, if you’re dealing with a manual transmission, foam implosion will occur between gears. In both cases, part pitting will take place.

In automatic transmissions, expect poor shifting and higher temperatures, as they depend on firm hydraulic pressure, not soft foam in making bands and clutches move.

The next thing that can happen is seal failure. Where there is a rotating shaft that gets inside a hole of an immovable part, there is a small part that prevents leakage – usually called a seal. In engines and transmissions, there are several seals and the most common culprit in their destruction is - guess what – excess fluid! Generally, the man-hour used in replacing them is huge! Thus, it isn’t too much of an effort that you ensure the oil is drained before damage occurs.

In many cases, seal damage calls for a transmission rebuilt. That, of course begins with removing the transmission out of the car, which entails labor cost. Transmission repair can cost high enough that the owner may just consider scrapping the old car to purchase a new unit. This is why it always pays to give enough attention to the transmission to make sure it will last.

How to check fluid levels

The correct way to check the fluid level depends on the kind of transmission your car has. For automatic transmissions, use the dipstick that’s located either near the in-line engine or the transaxle.

It is necessary to do the dipstick measurement only if the engine is running and take note of how increases in heat change measurements. When the transmission is cold, make sure the fluid does not reach the top.

Some automatic transmissions have no dipstick. If that is the case with you, you need to get measurements using the plugs at the transmission’s side. Check instructions from the manual.

Most manual transmissions don’t come with dipsticks but with plugs. Fluid levels for these are normally at the plug’s level, not above it. For cars with this type of transmission (and without dipsticks), checking must be done when the engine is off as it requires the use of a finger.

Warnings:

  • If the engine has been running for quite some time, hot components can burn you. Other conditions where a fluid level check is not advised include getting stuck in city traffic under hot weather and when your vehicle is towing another vehicle.

  • Keep any part of your body away from the radiator fan. For some brands and models, the radiator automatically starts even if the engine has already been turned off.

  • When fluid level is low, don’t refill right away. Always check for leaks before refilling.
  • How to avoid overfilling

    It’s easy to see the right level if one is dealing with plugs, but when it comes to using a dipstick, the advice is to add bit by bit or quart by quart to avoid overfilling.  Adding by half a quart each time is more preferable.

    Don’t let the dipstick mislead you. It may give a false reading. Turn on the engine and let it run idle. When the engine is already hot, it is time to get a measurement. Add a little each time until the reading says it is already full.

    When the engine is cool, the reading should fall on the top end of the “cold” range. When it’s hot, make sure that it reaches the top end of the “hot” range. For a warm engine, the reading should be between these two extremes.

    Most transmissions have a full capacity of 9 to 13 quarts. The amount of fluid to add depends on whether you are just adding to a remaining amount or you’re completely draining the transmission and will replace it to the full afterwards.

    When checking and refilling, make sure that your car is on a level surface.

    Other transmission matters to pay attention to

    Besides problems associated with too much transmission fluid or incorrect fluid level, avoid other issues such as burnt fluid, fluid contamination and dirty filters. Regular maintenance and checks can make your car and its transmission go a long way.

    About the Author Simon Adams

    Simon Adams here. a tech geek and an industry wizard. One of the original members of the CurateView team to offer unbiased product reviews.

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