Overfilled Transmission Fluid: Symptoms, Effects And How To Fix

Transmission fluid is the lifeblood of your automatic transmission. Without it, everything goes awry.

In brief, you must always drive with a sufficient level of transmission fluid. Too much or too little – both are dangerous.

This guide examines what you should anticipate to see if you overfill it – even by a small bit.

What Is Transmission Fluid?

Transmission fluid lubricates and cools your automatic transmission. It’s a completely separate thing from the gearbox oil used in traditional manuals.

Automatic transmission fluid – which I’ll occasionally refer to as ATF – is also used in the torque converter. It’s a complicated system composed of an impeller, a propeller, and a stator. This allows you to stop without stalling the engine.

Traditional transmission fluid was, unsurprisingly, derived from crude oil. These days, they’re much more likely to be artificial.

As might be becoming clear, transmission fluid is vital. Overfilling it could lead to severe problems.

How Do I Know If I’ve Overfilled My Transmission?

The most evident sign of overfilling your transmission with ATF is the dipstick. You should use this while filling up to ensure you never exceed the limit.

The dipstick might show your transmission fluid levels are higher than the MAX mark. That means – at the risk of sounding arrogant – there’s too much in it!

Driving on an overfilled transmission could be hazardous. The internal components and torque converter feel excessive strain and are increasingly prone to fail.

You will likely observe several additional symptoms along with the elevated ATF level on the dipstick.

Symptoms Of Overfilled Transmissions Fluid

Here are some of the most evident signs of overfilled transmission fluid.

High Transmission Fluid Level

I’ve mentioned this one before. It’s remarkably obvious but worth listing here anyway.

You’ll see it on the dipstick if you have an excessive transmission fluid level.

Of course, you need to confirm this manually, following the instructions in your owner’s manual.

Transmission Warning Light/Notice

Most contemporary cars will warn you when there’s a problem with the transmission. Sensors often pick up on issues long before we realize they’re present.

You might notice a transmission warning light or an alert on your display. If it’s about the transmission and you’ve added excessive ATF, chances are they’re connected symptoms.

Heavy Gear Changes

When you’re in Drive and the car changes gear, you might feel more of a significant *thunk* than usual. If this happens on repeat, you can be sure there’s a developing transmission problem.

In reality, this could stem from any internal component (or a mount), but the transmission fluid is a common culprit.

In short, the ATF isn’t lubricating the gears. This lack of cushioning means they ‘clunk’ into position instead of smoothly gliding.

Rough Revving (Especially Acceleration And Idle)

The above video demonstrates how a torque converter works. It’s especially relevant for this brief section.

A coarse idle and poor power while accelerating could be symptoms of almost anything. This includes high levels of transmission fluid.

Too much transmission fluid might damage the torque converter or affect its flow.

It’ll also otherwise stop the gears from meshing smoothly. This results in that sensation of the car struggling.

Overheating Transmission

Your transmission could start to overheat, even though you have too much fluid as opposed to not enough.

Because there’s too much ATF in your transmission, it isn’t circulating as it should. Increased pressures due to more volumetric space occupation also mean elevated temperatures.

The fluid deteriorates and begins to lose its capacity to cool.

These combine to result in an overheating transmission. This is often displayed via a dedicated warning light or message.

Sounds From The Transmission

Transmissions aren’t quiet by any stretch of the imagination. But they shouldn’t be clunking, excessively vibrating, screeching, or juddering.

Any unusual sounds coming from your engine bay could be caused by the transmission. In turn, the underlying issue could be excessive transmission fluid.

Car Struggles When Slowing Down (In Gear)

The torque converter is also responsible for slowing down. Without it, the transmission would be fighting you as you brake – a dangerous situation!

Torque converters utilize the transmission fluid. Problems with it can be caused by high ATF levels.

Foamy Or Bubbly Transmission Fluid

The transmission fluid should still be vivid and clear. Bubbles or foam means the liquid is being churned up by the internal components too much.

This happens when there’s too much of it.

You’ll also notice it when the transmission fluid is stale. Either way, you need a system flush!

Broken Transmission

This is the most adverse-case scenario and should only happen if:

• The transmission has been massively overfilled
• You drive your car for an extended period with overfilled transmission fluid.

The torque converter is the most probable part to go. It’s handling the brunt of the pressure applied by excess fluid.

That said, any mechanical component could fail. They’re all lubricated by the fluid and thus aren’t being safeguarded or appropriately cooled.

Is It Bad To Overfill Transmission Fluid?

Indeed.

You mustn’t overfill transmission fluid, the same way you mustn’t overfill motor oil.

Anything above the MAXIMUM level on the dipstick is too much.

If you put too much transmission fluid in, you should remove some. Only drive once you’re at a level appropriate for your car.

What Should You Do If You’ve Overfilled Transmission Fluid?

I wouldn’t advise driving anywhere because it’ll damage your transmission. Yes, you might get away with a quick trip to the mechanic, but I don’t condone risking it.

Overfilling your transmission can be readily remedied at home. You might need help from a mechanically-adept friend, though.

Here are two techniques you could try if you know what you’re doing.

1. Transmission Drain Plug

Nearly all modern cars have a transmission drain plug.

This works in exactly the same way as an engine oil drain plug. It’s loosened (or removed entirely) to allow the transmission fluid out.

Only do this if it’s safe to do so and you know what you’re doing.

Using axle stands, a drain pan, and a suitable tool, the drain plug can be loosened. In some cases, it’s straightforward to only let a small amount out. Sometimes, this is more difficult, and it might make more sense to flush the whole lot and refill it.

Remember to reinstall the plug and never start your car until you’re out from underneath it and it’s lowered off the axle stands.

You don’t need to remove the bottom half of the transmission (like some blogs say) unless it’s a sealed unit. But that’s not an easy job; that’s one to leave to the professionals.

2. Extraction Tool

The alternative is getting yourself a removal hose.

Poke the end down the transmission dipstick housing. Next, use the syringe on the opposite end to remove a specific amount of transmission fluid.

Now, recheck the levels. Repeat this procedure (and add more if necessary) until the ATF is at an appropriate level.

3. Call-Out Mechanic

If it comes to it, use a call-out mechanic. This is undoubtedly the most expensive option, but it’s the best way forward if you’re really out of your depth.

You shouldn’t drive if you have too much transmission fluid, so a call-out mechanic is the next optimal thing.

They’ll most likely perform one of the two techniques mentioned above. You’ll be on your way again in no time.

For tranquility of mind, this is the option for you, and thus the one I officially recommend.

Conclusion

So, to sum up – your transmission fluid must be at a safe level. If it’s too high (or too low), you’ll find yourself in a costly or even perilous situation.

It will prevent an expensive transmission repair or replacement.

Keep an eye on your transmission fluid, and check it as part of regular maintenance. That way, you can be certain you’re doing your bit to look after your vehicle.

Stay safe out there!