Engine Coolant in Automatic Transmission Case. Nature of the Problem and Possible Solutions.

Transmission repair specialists frequently have to deal with such an issue as the mixing up of engine coolant (antifreeze substance) with the automatic transmission fluid. It is a very serious problem which can lead to the transmission failure and highly-priced repair or even transmission replacement. In this article, we will consider causes of this problem and possible solutions.

Typical car cooling system

The design of modern vehicles allows the use of the engine and transmission under severe conditions. In the process of driving, car components (engine and transmission) are exposed to high temperatures, thus a certain amount of heat must be removed to avoid thermal destruction of automatic transmission elements. For this purpose, cars are equipped with a special cooling mechanism which ensures heat exchange between two environments, namely, between automatic transmission fluid and engine coolant. Coolants are responsible for keeping a temperature balance at a certain level, which ensures a long-term operation of crucial car components.

Design of transmission cooling system

As a rule, all “old” transmissions were cooled by supplying oil to the engine radiator, which had not only engine pipes for the engine coolant, but also connection hoses for circulation of transmission oil. The oil circulated inside the radiator via a special pipeline. Over the years, this basic design solution was modernized by automotive engineers in every possible way: additional air coolers, valves, filters, thermostats, etc.

Today, engineers prefer to install a special heat exchanger (cooler) directly on the automatic transmission case. This solution enhances the efficiency and durability of automatic transmissions.

Automatic transmission fluid cooler (heat exchanger)

Based on the above, it can be concluded that ATF and engine coolant can get mixed in the faulty engine cooler (radiator) or out-of-order automatic transmission cooler. There are no other points of contact for these fluids.

“Victim” of engine coolant leakage

The design of modern automatic transmissions includes friction discs (also known as friction clutches). These clutches are responsible for meshing between gears (like a clutch in manual transmissions). At a certain moment, these clutches close up (with the help of oil pressure) and stop the necessary gear (a certain gear is engaged), at another moment they open up — the gear starts rotating (the gear is disengaged).

In terms of design, friction clutches (discs) consist of two main components:

• Metal disc (hard part). These discs are in mesh with the automatic transmission case, and almost always remain in fixed position.
• Friction lining (made of various material combinations; cheap options include cellulose and durable options are Kevlar, Carbon, etc).

It is worth noting that friction discs in old automatic transmissions were only one-sided (without friction linings). Modern automatic transmissions are equipped with upgraded friction discs with friction linings made of modern materials. Friction discs are assembled in friction clutch packages. Standard 4-speed automatic transmissions have 2-3 clutch packages, depending on their design.

Automatic transmission clutch package

Friction clutches can last long under normal operating conditions. Automatic transmission clutches, however, easily absorb water. When friction clutches are exposed to moisture (in our case to coolant or antifreeze substance), it may lead to corrosion of metal discs and friction linings come unglued. According to numerous studies, even a small amount of water or engine coolant will be enough to cause serious damage.

That’s how friction clutches (plates) look like after a contact with engine coolant

Main causes of the problem

• Micro-cracks in engine cooler or automatic transmission cooler caused by car accidents. Dents, which may seem harmless at first sight, can lead to development of micro-cracks which result in leakages of engine coolant.
• It is recommended to change cooling fluid regularly (every 3-5 years). If drivers ignore this recommendation, it can lead to corrosion of aluminum-made radiators and coolers and subsequent leakages.
• Pressure issues in the cooling system.

If the antifreeze substance gets inside the gearbox, it will lead to the following consequences:

• Friction linings gradually come off;
• Transmission rubber elements swell, become flabby, and lose their sealing qualities, resulting in leakages and functional disorders;
• Valve body and electronic elements of the transmission get out of order.

If you do not take urgent measures, the transmission will be completely damaged.

How to prevent the problem

If you want to prevent the mixture of transmission fluid and cooling liquid, it is necessary to do the following:

• Regularly, check the level and state of ATF. If the fluid has a pinky color, then the transmission fluid must be changed;

When ATF mixes up with antifreeze substance it looks like a strawberry milk shake

• Periodically, check the level of coolant in the engine radiator. Pay attention to presence of oil (oil emulsion) in the expansion tank. If you notice that something is wrong, it is necessary to visit the nearest repair shop.

What if engine coolant (antifreeze substance) mixes up with transmission fluid?

The first rule in such situation is: never try to flush the automatic transmission! This measure is absolutely pointless – the friction coating (especially particular to that consisting of cellulose) absorbs the water and glycol and this process is irreversible. Several “heating-up-cooling-down” cycles will do its job and the coating will come off.

This video proves the point

If you have to deal with the abovementioned issue, we recommend the following measures:

• Complete automatic transmission disassembly;
• Flushing and replacement of all friction elements;
• Replacement of rubber elements;
• Torque converter maintenance services;
• Replacement of filters and change of transmission fluid;
• Finally, it is necessary to eliminate the cause of the problem. It is necessary to replace the radiator or cooler. You can install a remote air-cooling radiator.

Learn how to fix a coolant leak

However, sometimes the level of damage to metal and electronic parts of the transmission is so high, that the price for transmission repair may exceed the price for remanufactured or used transmission. It such cases, it is better to replace the damaged transmission unit. In any case, before making any decision, it is better to get expert advice from transmission repair specialists and to visit a reliable repair shop to perform required services.