What Will Happen When You Overfill Transmission Fluid?

All of us understand that transmission fluid plays a really important role in keeping the engine of your car run smoothly. Due to friction, the transmission produces a lot of heat, and to keep it from damaging your car, you need to apply transmission fluid for the engine.

Many people rarely change the transmission fluid, and even those who usually leave this task to a professional service garage. In fact, you can replace this fluid on your own just by using a few tools available. But how do you know the suitable transmission fluid level for normal functioning of the car?

How is The Suitable Level of Transmission Fluid?​

Generally, you should only add about half-a-quart fluid each time. Even when the dip-stick is really not full, it would show that. Start the car and let it running for approximately 5 minutes, then check the level again when the engine is already warm. Add in as much transmission fluid as needed till the dip-stick shows full.

In a hot engine, the level of transmission fluid needs to be on the upper part of the hot mark, while in the cool one it must be on the upper part of the cool mark. Make sure that the fluid level is also in the safety zone between the 2 marks at a warm engine.

Most transmission fluids often take from 9 to 13 quarts to be full completely. Depending on whether you are replacing, draining or topping, the transmission fluid amount that you add will vary. Again, remember to add in little amount at the same time to prevent putting too much.​

What Will Happen When You Overfill Transmission Fluid?

If you put too much amount of transmission fluid to the engine, you will see that it might foam, which can lead to unpredictable gear shifting. In addition, transmission damage as well as oil starvation are other possible problems.

In a transmission or an engine, foaming happens when rotating elements (rotating parts in crank-shaft weight, tranny in the engine) splash into the overfilled oil/fluid reservoir or crankcase. This will result in excessive fluid temps, which make the transmission fail and the tranny fluid degrade very quickly.

When you overfill an automatic transmission, the fluid would foam, resulting in problems with transmission damage, gear shifting or oil starvation. While an overloaded manual transmission would lead to fluid-leak in the vent and gear shifting becomes an issue once the clutch is pressed. All transmissions, auto or manual, have some ways to relieve excess pressure.

Putting too much fluid could also cause damage of elements and early failure due to excess pressure, which is in shift from minimum to maximum (often 300 PSI) and makes some elements of your car totally unstable.

When you attempt to change or reverse the gears more, the problem could get even worse. You can notice easily how that would do a lot of damage to the transmission. The pressure could result in friction and break parts, push out snap ring easily, leading to serious damage or sudden failure.

Most modern cars are designed with transmissions that have a pressure valve to controls pressure after a pump. Nevertheless, as mentioned earlier excessive pressure can lead to the wearing out of several elements, including the valve, thus make it fail. As a result, this failure will in turn generate pressure related issues in other components of engine. In other words, putting too much fluid can result in to pre-mature damage of the vehicle’s engine over time. In addition, it might most likely prevent any warranty that you may have if the reason for this failure is attributed to overfilled transmission fluid.

In fact, there are still some car models that are made with transmissions which could not be overfilled thanks to modern design, which has a hole at its side to allow any excessive fluid to come out.

What Should You Do After Overfilling Transmission Fluid?​

When you overfill the transmission, you can have it resolve by a service garage or drain it on your own by applying a filler tuber changing the cooler line or taking the pan drain plug out. It would take time to suck out the transmission fluid but you just need to hold the filler tube till it nearly reaches your mouth’s cap, then pull out the tube by your thumb, stick the end to a can and drain it.

You can also take advantage of some reasonable extraction pumps, which are available in most car parts shops. After draining, you will have to change the fluid to the suitable level if it is not in appropriate condition.

Wipe a dip-stick on the white cloth or wipe, and check the color left, which needs to be clear. If you see several black spots or it is fairly brown, you should get the transmission fluid replaced immediately. Due to dirt, temp degradation, metal or friction particles, the thickening of transmission fluid can block the drain and lead to foaming.

If you are interested in driving your vehicle in stressful condition where transmission is hotter than usual, you should frequently check the transmission fluid for burning and wearing out.

Several drivers will say replacing the transmission fluid is not really necessary, but it is actually not true. The heat produced when running can get so hot that it starts to lose the lubricating capabilities and the seal will start to harden, which lead to pressure losses and leaks. As a result, the transmission will be damaged in those conditions.

To sum up, keeping a close eye on the amount of transmission fluid that you put can save you a huge amount of repair expense in the long term.​

John Henry
 

I am John Henry and I have begun to work in automotive industry since the 90s, specializing in car rebuilding and repair. After nearly two decades of working in this complex section, with extensive experience in repairing, troubleshooting and maintaining thousands of cars, I started to work as an auto blogger to share my practical knowledge as well as skills with car owners all around the world through a wide range of articles in online magazine.

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