Fluid Foaming (bubbles) in Automatic Transmissions: Causes and Possible Solutions of Foamy ATF


Fluid Foaming (bubbles) in Automatic Transmissions: Causes and Possible Solutions of foamy ATF

It is well-known that fluids (ATFs) in automatic transmissions serve not only as a lubricant, but also perform a wide range of other tasks. First of all, ATF is a working medium that controls the transmission operation in the valve body unit and transmits torque in the torque converter. ATF also helps to cool the transmission unit during active transmission operation.


During regular maintenance services, drivers of cars equipped with automatic transmissions sometimes can notice numerous bubbles on a dipstick when checking a transmission fluid level/condition. As a rule, this symptom indicates certain faults in the transmission operation. In most cases, transmission fluid foaming is caused by abnormal ATF levels. In this article we will consider the main causes of these problems, its negative consequences, and possible solutions. You can use our tool to check which type of transmission oil is used in your car and how much of it you will require. If you need a transmission mechanic in your area use this transmission shops map to find closest and reliable transmission service.


If transmission oil (ATF) is normal colour

Symptom
Possible cause
Solution
Bubbles on dipstic, ATF is clean, transmission is slipping or engaging slowly
Insufficient ATF level, the oil pump also intakes the fluid with air
Adjust the fluid level
Depressurization of the oil passage, leakages of ATF through seals and gaskets
Inspect the transmission unit for ATF leaks, at a local transmission shop


Symptom
Possible cause
Solution
Bubbles on dipstick, but ATF is clean, transmission
engages smoothly
Result of mixing different transmission fluids
Do transmisison flushing, at a local transmission shop
Use of improper fluid type
Do transmisison flushing, at a transmission mechanic
Use of “old” ATF
Check fluid type, transmission flushing is recomended
Overflow of the transmisison fluid level
Remove excessive oil off

Check out our transmission shops map to find closest and reliable transmission specialist in your location.

You can use our tool to check which type of transmission oil is used in your car and how much of it you will require.


If oil (ATF) is strange colour (light brown or dark brown)

Symptom
Possible cause
Solution
ATF smells like burned and is brown colour
Transmission is damaged. Due to overheating, and ATF is "cooked". Transmission might have worn out friction discs.
Visit your transmission mechanic
Aggressive driving style
Check safe driving tips, consult a local transmission shop
Contamination or failure of the automatic transmission filter
Check filter
Use in hot weather with stop-and-start driving
Check safe driving tips, consult a local transmission shop


Symptom
Possible cause
Solution
The fluid has a milky brown appearance
It indicates coolant contamination. There is probably a leak in the ATF oil cooler inside the radiator that is allowing coolant to mix with the ATF.
Visit your transmission mechanic
Engine fluid used instead of ATF
Do transmisison flushing, at a local transmission shop

Check out our transmission shops map to find closest and reliable transmission specialist in your location.

You can use our tool to check which type of transmission oil is used in your car and how much of it you will require.


Causes of ATF foaming

In most cases, bubbles on transmission dip stick caused by insufficient ATF level or its overflow and you might need to contact your local transmission mechanic. If the fluid is above the norm, the foam is formed when moving elements inside the transmission unit “grab” the fluid in the pan and make ATF foamy. If the fluid level drops, the oil pump also intakes the fluid with air.Depressurization of the oil passage, leakages of ATF through seals and gaskets can lead to the fluid foaming, too. In some cases, ATF becomes foamy because of severe contamination or failure of the automatic transmission filter.


That’s how foamed ATF looks like


The foam can also appear as a result of mixing different transmission fluids, i.e. foaming is the result of a chemical reaction that causes the loss of fluid properties. The thing is that compositions of modern ATFs include a great number of chemical additives, which ensure proper operation of transmission units. As different transmission fluids include different sets of additives, they often turn out to be incompatible.


For this reason, it is prohibited to mix mineral and synthetic transmission fluids. Disregarding this rule can lead to fallout of precipitation that pollutes operating surfaces, clogs valves, channels, and other components. One more reason for ATF foaming can be the use of “old” ATF. Manufacturers recommend changing transmission fluid every 60,000 kilometers. Aggressive driving style, driving in hot weather with stop-and-start driving can reduce the service interval to 30-50, 000 kilometers without waiting until ATF starts foaming and blacken.


Negative consequences of ATF foaming

It should be noted that if you see large and rare air bubbles on the dipstick during ATF check after intensive driving with high RPM rates, this does not mean that the fluid is foaming. But when there are many evenly spaced bubbles on the dipstick, it is a dangerous symptom that requires a detailed diagnostics.



The process of ATF foaming can be quite harmful for any automatic transmission. The level of transmission fluid and its density are crucial for proper operation of the automatic transmission unit. The appearance of foam, in turn, leads to negative changes in ATF density. As a result, the foamed fluid becomes compressible and cannot create the necessary pressure on friction packages. This leads to oil starvation, slippages of clutches, etc. With ATF foaming, wear products quickly contaminate the oil and hydraulic system, damage valve body channels, destroy valves, etc. Moreover, it should be remembered that automatic transmissions are extremely sensitive to overheating. The appearance of foam in ATF leads to significant reduction in heat removal capacity, thereby increasing the risk of the transmission unit overheating.


Possible solutions and recommendations

At the initial stage, the main symptoms of ATF foaming are kicks and jolts when driving and shifting from P and D or R. Moreover, automatics can also jerk when braking. In any case, if the transmission starts jolting, then it is time to check the transmission fluid. As has been mentioned before, the main reason for ATF foaming is the incorrect fluid level. Ii it is the case, then it is necessary to adjust the fluid level. (Note: the fluid level should be measured after a proper warm-up of the transmission unit.)


ATF levels


If there is a fluid overflow (when the fluid level is higher than the HOT mark), the excessive fluid must be removed. In case of the fluid overflow, the foaming will not appear immediately after the engine start, but after driving under loads and at high RPMs. The ATF removal can be done with a special fluid syringe and a thing tube.


Learn how to check ATF level accurately


In case of a low ATF level, it is necessary to inspect the transmission unit for ATF leaks (pan, cooling pipes, half-axles installation locations). If there are no visible leaks, then it will be enough to add the missing amount of ATF. At the same time, it is necessary to use the same ATF that has already been used in the transmission unit.


As has been mentioned above, there are several reasons for appearance of foam in ATF. If the car owner notices bubbles on the dipstick, then it is necessary to check the ATF level as well as the general condition of the fluid (color, smell, transparency, viscosity). If there is visible ATF foaming, then it is recommended to stop using the vehicle and tackle the problem without any delays, since driving with foamed ATF can lead to the transmission failure and consequent costly repair of the unit.



Finding quality transmission insights and reliable information is not an easy task for transmission specialists who are often either busy with transmission repairs or have their hands covered in oil after a transmission fluid change. All in all, we may be exaggerating a bit but finding these materials is a timely process indeed. We at go4trans.com have got it covered for you! There is a lot you can learn about transmission problem solutions and new transmission models being launched, we also try to interview transmission industry professionals so they can share some of their experience and stories with our readers. We have also included what we find to be events of interest for anyone related to the transmission industry: you check dates, venues, profile and more details on the upcoming industry events. We have got food for thought that you need!

You can add your own material at go4trans.com. If you want to share a story related to your business or if you want to highlight some industry news and introduce it to fellow specialists, we encourage you to submit your material to us by contacting us through the contact form or this email: info@go4trans.com.



Latest articles

There are so many problems with electrification development. No infrastructure, no stations to charge the batteries. And charging takes too long. Also, many cars don’t match the charger, many vehicles have to

In the last couple of articles, we used terminology relating to pressure control solenoids such as PWM, Frequency, and Duty Cycle. In this article I thought I would go into depth on what these terms really mean and how they relate to

As far as I know, we are the only company that manufactures frictions clutch plates, steel clutch plates, and similar products, that is vertically integrated. In other words, not only can we test new designs, we also develop our own resins, and we can design and make our paper.

Share this page with your friends