Popular articles

Probably every transmission repair specialist was keen on LEGO constructions or at least enjoyed making some minor things with their hands. Here's the game taken to a new level of creativity!

Modern auto industry is full of sophisticated drivetrain technologies which are supposed to make your driving experience even more pleasant and trouble-free. Despite a great abundance of sophisticated technical solutions, it is highly likely that very few people know a transmission solution operating like a manual CVT.

Over recent years engineers developed a lot of gear shifting solutions for different car brands, which may seem a bit unusual for oldtime drivers. In this article we will review the most peculiar gear stick technologies and provide video materials related to these technologies.

Only few people know about transmission concepts which were popular 70-90 years ago. For men of today, these gearboxes may seem very unusual and weird, but even now some gearboxes that date back to those years are quite competitive in comparison with modern transmissions.

Nowadays Extroid CVTs are commonly known as “toroidal” due to the fact that the working surface of driving and driven discs in this transmission has the form of a torus. Extroid CVT is not a V-belt transmission, but a friction drive CVT.

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.

Popular articles

Probably every transmission repair specialist was keen on LEGO constructions or at least enjoyed making some minor things with their hands. Here's the game taken to a new level of creativity!

Modern auto industry is full of sophisticated drivetrain technologies which are supposed to make your driving experience even more pleasant and trouble-free. Despite a great abundance of sophisticated technical solutions, it is highly likely that very few people know a transmission solution operating like a manual CVT.

Over recent years engineers developed a lot of gear shifting solutions for different car brands, which may seem a bit unusual for oldtime drivers. In this article we will review the most peculiar gear stick technologies and provide video materials related to these technologies.

Only few people know about transmission concepts which were popular 70-90 years ago. For men of today, these gearboxes may seem very unusual and weird, but even now some gearboxes that date back to those years are quite competitive in comparison with modern transmissions.

Nowadays Extroid CVTs are commonly known as “toroidal” due to the fact that the working surface of driving and driven discs in this transmission has the form of a torus. Extroid CVT is not a V-belt transmission, but a friction drive CVT.

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