Bubbles In Transmission Fluid: Everything you Need to Know

Aside from lubricating purposes, fluids (ATFs and CVTs) play other essential roles in automatic and continuously variable transmission. ATF in an automatic transmission, for example, lubricates the internal automatic transmission parts for proper operation, controls the workings in the valve body, and sends power and torque to the torque converter. It is also a cooling agent in the transmission unit that keeps the transmission at normal operating temperature during operation.

During regularly scheduled maintenance, drivers with a continuously variable or automatic transmission may notice bubbles in transmission fluid when inspecting the state and level of the fluid.   Bubbles on the transmission dipstick indicate issues in the transmission. It may result in catastrophic damages if not handled on time.

The common causes of these bubbles are low or overfilled transmission fluid and air in the system. So, this article has provided sufficient information on the causes, symptoms, and how to remove bubbles from the transmission fluid.

Wait, scratch that! Let’s get high.

What Causes Bubbles in Transmission Fluid?

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In most cases, the common causes of fluid boiling or bubbles are improper fluid levels and air in the system. In either case, you may have to contact a certified mechanic to track down and fix the culprit. If you have overfilled transmission fluid, the bubbles are created when reciprocating internal transmission components pull the fluid from the crankcase without breathing space.

Similarly, if you have a low fluid, the oil pump sucks the fluid along with air. Other causes of bubbles in CVT transmission fluid include fluid leaks via gasket and seals, wrong oil type, and depressurization of fluid galleries. In some other cases, the bubbles and foaming are caused by a lousy transmission filter and huge contaminants in the fluid.

Transmission fluid boiling can also occur as a result of pouring more than one fluid into your tranny. That is to say, the chemical reaction of pouring different transmission fluids equals bubbles. It is worth noting that formulation ATFs and CVTs include several chemical and functional additives for the proper operation of car transmission. As different additives are used in the fluid formulation, they often become incompatible with mixing.

Enough said it is, therefore, not recommended to mix two or more transmission fluids.  Mixing transmission fluids may cause a clogged transmission vent, channels, valves, and other system components failures. It can also pollute the operating surface.

Another cause of bubbling is the use of old ATF. Auto manufacturers have a specific duration that ATF or CVT should last in your tranny. While the time of changing transmission fluid differs from manufacturer to manufacturer, on average, transmission fluid should be changed at every 60,000 miles.

Driving in hot weather conditions, stop-and-go driving, and aggressive driving habits may reduce the replacement interval to 40,000 to 45,000 miles without waiting for the fluid color to change to brown or start foaming.

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Q: What are the symptoms of bubbles in transmission fluid?

At the initial stage, the air in transmission fluid symptoms, one will notice is a display of jolts and kicks when driving and shifting to a different gear range. In any case, automatic transmission can jerk when stepping on the brake pedal. Regardless, it is appropriate to check your fluid level if the car starts to jerk when breaking because it could result from improper fluid level.

Other symptoms of air in transmission fluid include bubbles on the transmission fluid dipstick.

Q: How do I remove air from the transmission?

Having known the causes and symptoms of foaming transmission fluid, it is imperative to learn how to get the air out of transmission fluid.

Since there are several causes, there are also different ways to get rid of the bubbles. If the foaming results from a low fluid level, the best solution is to inspect the fluid and adjust it appropriately.

On most vehicles, you need to check the fluid level when warmed up and running at an average operating temperature. Other cars like Honda products require warning the engine to keep it at normal operating temperature but must be turned off before checking the fluid level.

If you see bubbles on the dipstick, check the overall conditions (viscosity, smell, color, transparency).  If you recently mixed the trans fluid, drain and replace it with a recommended fluid for your car. Do not continue driving with bubbles in transmission fluid. It can endanger your transmission unit.

Q: Are bubbles in transmission fluid normal?

Tiny bubbles in the transmission fluid are expected because the transmission incorporates reciprocating components that move inside the transmission fluid. But if the liquid is full of foams and bubbles, you’re probably driving with an overfilled transmission fluid.

Q: Should I change the brown transmission fluid?

A dark brown or black transmission fluid indicates a dirty, contaminated, or oxidized fluid that is incapable of adequately lubricating the internal transmission moving components. Oxidation is bad for transmission fluid. It will damage system components if you fail to change them on time.

Q: Can I check my transmission fluid?

Yes. It is recommended to change your transmission fluid after covering certain miles. As alluded above, some vehicles require checking the transmission fluid when the engine is running at an average operating temperature. Others require warming the transmission before checking the fluid after turning off the engine.

 Consult your owner’s manual or service manual to know when and how to check your transmission fluid.

Q: Can too much transmission cause shudders?

The primary function of the transmission system is to lubricate the reciprocating system components and minimize friction between them. However, it won’t carry out this function properly if it is overfilled. The outcome will be shuddering transmission. Why is it so?

Overfilled transmission fluid will cause bubbling and foaming in the gearbox. This happens when the reciprocating parts submerge into the overfilled fluid. It then causes chemical reactions, resulting in transmission shuddering.

Q: Is it better to change or flush transmission fluid?

Transmission fluid change is a cheaper option that’ll help restore your transmission unit to running optimally. It is a quick-fix job that a car owner can do without consulting a technician.

In contrast, transmission fluid flush is costlier. It is a more complex job that needs professional attention and takes more time, but it’ll get rid of any contaminants that have been stored in the system.

Final word

Bubbles in transmission fluid should be a significant concern to you. It can cause catastrophic damages to any CVT and automatic transmission.

Ensure you regularly check your transmission fluid state and level. Running with an appropriate transmission fluid level and the condition is essential for the proper performance of an automatic gearbox.

Bubbles will pretty much lead to system overheating. Do not forget that your automatic transmission is susceptible to overheating. Apply the measures outlined above whenever you notice foaming in your tranny. Consult your mechanic if it doesn’t curb the issue.

Osuagwu Solomon

Osuagwu Solomon is a certified mechanic with over a decade of experience in the mechanic garage, and he has over five years of experience in the writing industry. He started writing automotive articles to share his garage experience with car enthusiasts and armature mechanics. If he is not in the garage fixing challenging mechanical problems, he is writing automotive repair guides, buyer’s guides, and car and tools comparisons.

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