Cars,  Auto Engines

What Happens When Too Much Transmission Fluid Is Added

Your transmission fluid is of great importance for the smooth running of your vehicle’s engine. The transmission generates a lot of heat due to friction, and to prevent this heat from damaging your vehicle, you have to add transmission fluid to the engine.

When you add too much transmission fluid, damage to your vehicle can occur. Here are some things that might happen: oil starvation, erratic shifting, transmission damage, excessive pressure resulting in immediate or long term damage. 

A majority of people seldom replace the fluid, and even those who do often leave the replacement to a service garage. You can change the transmission fluid yourself using only a few tools, however the level of fluid is important to the smooth functioning of the engine.

TIP: Ensure you only use the recommended transmission fluid for your engine because using the wrong one can end up damaging some parts of your vehicle. Go through your owner’s manual to see if you need a specific type of transmission fluid for the vehicle. The most affected auto engines in this situation are the latest ones that usually come equipped with electronically controlled transmissions.

How Much Transmission Fluid Should You Add?


You should only put in fluid about half-a-quart at a time. The dip-stick might show full, even when it is really not. Start the engine and leave it running for about five minutes, then recheck the level after the engine is warm. Put in as much fluid as needed until the dip-stick reads full.

The transmission fluid level ought to be at the upper end of the cold mark when the engine is cool, whereas in hot engine it should be at the upper end of the hot mark. Ensure the level of the fluid is in the safe zone’ between the two marks in a warm engine.

Most transmissions usually take about 9 to 13 quarts to fill completely. The amount of transmission fluid you put in will vary depending on whether you are just topping it up or draining and replacing it all. Again, put in little fluid at a time to avoid adding too much. That said, let’s look at what really happens when you add in too much transmission fluid.

Overfilling and What It Means It Does To Your Vehicle


If you add too much transmission fluid, you will notice that it may foam, and that can bring about erratic gear shifting. Some other problems that may arise include oil starvation and transmission damage.

In an engine or a transmission, foaming occurs when rotating parts (rotating gears in a tranny, crank-shaft weights in an engine) splash in the overfilled fluid/oil crankcase or reservoir. This splashing results to excessive fluid temps, the transmission end up failing, and the tranny fluid as well degrades very quickly.

When an automatic transmission is overfilled, the fluid foams, leading to gear shifting problems, oil starvation as well as transmission damage. On the other hand, an overfilled manual transmission results in fluid-leak from the vent and the shifting the gear becomes a problem when the clutch is depressed. All transmissions, auto or manual, have some ways to relieve excess pressure.

Adding too much transmission fluid can also cause early failure and damage of parts as result of excess pressure. The pressure in shift from low to maximum in this condition making some parts of your vehicle completely unstable. A pressure jump from very low to 300 PSI gauge’s or more is what we are talking about in this situation.

When you try to change the gears more so on the 3-4 and 2-3 as well as the reverse gears this condition can become even worse. You can easily guess how that could do a lot of damages to your transmission. The pressure would result in friction and easily push out snap rings, break parts, etc. Causing sudden failures and/or serious damage.

Modern vehicles have transmissions that include a pressure valve which regulates pressure after the pump. However, as previously mentioned excess pressure can result to pre-mature wearing out of some parts – the valve included, thus causing it to fail. Failure of the valve can in turn create pressure related problems in other engine components.


So yes, adding too much transmission fluid can lead to pre-mature failure of the car’s system over time, and may most likely void any warranty you may be having, if reason for the failure is found to be the presence of excess fluid.

However, there are vehicles that are equipped with transmissions that cannot be overfilled due to their design. They may have a hole on the side to allow any extra fluid to flow out.

How to Fix Too Much Transmission Fluid

If you overfill your transmission, you can fix the problem by draining it yourself or going to your service garage. The solution is simply to drain off the excess transmission fluid by using a pump to siphon it out (Amazon Link), draining off by taking out the pan drain plug (for cars that are equipped with it) or removing the cooler line.

You might have thought about siphoning it by mouth. It will take time sucking out the fluid and you may accidentally get some in your mouth if not careful. It's not recommended, but if you do, use your thumb on the top of the tube to prevent the oil from draining out and use a suitable container to drain it off into.

You can also make use of one of those affordable extraction pumps you find in most auto parts stores. Once you are done draining, you will need to replace the fluid to the appropriate level if the fluid was not in good condition.

Check the Dip Stick

This is an oil dip stick. My truck has a sealed transmission, so no dip stick. 

You may see a reddish colored dip stick handle. If the only handle you see is the yellow oil dip stick, you may have a sealed transmission. Wipe the dip-stick on a white wipe or cloth, and check the color. It should be pink.

If it is brownish or if you find some black spots in the fluid, you must have the transmission fluid changed immediately. Thickening of the transmission fluid due to friction/metal particles, temp degradation, or even just pure dirt can clog the drains and cause foaming.

If the oil is black and smells burned, then you may have already damaged your transmission, and getting new fluid will likely create problems because of the damage and clogs that have occurred with old fluid.

TIP:  When the oil is black and you flush your transmission fluid and replace it with new fluid your gears may start to slip because the clutch packs have started to wear out. In addition your valve body may start to clog, causing poor shifting also. It's likely that you'll need some expensive repairs. (More info from ChrisFix Video)

Should I Replace My Transmission Fluid?

If you are fond of driving your car in stressful conditions where transmission gets hotter than normal, you should regularly check the fluid for wearing out and burning.

Some people will tell you that it is not really necessary to replace the transmission fluid, but it does eventually wear out. The heat generated when driving can at times become so hot that it begins to lose its lubricating capabilities, and the seals will begin to harden, resulting in leaks and pressure losses. Eventually, the transmission will wear out under these conditions.

Look at your owner manual to find out how often and what type of transmission fluid you'll need. If you have a sealed transmission, you have to change your fluid less often but get it inspected at recommended time period or before if you've run your engine hard.

Keeping an eye on the condition and the amount of transmission fluid you have, and save yourself a huge repair bill in the long run.

Additional Questions

How can I check my fluid in a sealed transmission?

If your a DYI kind of person, then you can remove the bolt that holds in the transmission fluid in or the check level bolt. You may need to do some research about where the bolt is located at bottom of your vehicle and how it operates. Most owner manuals don't have that information, so you may need to ask a mechanic if you can't find it online.

Getting a mechanic to help you check the fluid might be the easiest way, without causing more problems caused by incorrectly checking a sealed transmission. 

What should my transmission fluid look like?

Your transmission fluid should be a pink color when wiped on a white paper towel. If it is brown, it's time to change it. It should also appear very similar to motor oil in viscosity. If it seem too thick, that may be an indication of a problem.