transmission heat exchanger

Symptoms of a Failed or Bad Transmission Oil Cooler

In Transmission by Magnus Sellén3 Comments

transmission oil cooler symptoms

The oil cooler is an essential component of every vehicle, whether it is a sedan, SUV, or a full-sized truck.

It is designed to keep your vehicle running smoothly day after day. Whether you own an expensive vehicle or a cheap day car like a Toyota, you need to take care of the oil cooler to keep it running perfectly.

Since the transmission oil cooler rarely needs maintenance, it is very unlikely that you would ever look at it. Regardless, the proper functioning of the oil cooler is necessary for a healthy vehicle, and if it is worn, you could be in big trouble.

Functions of an Oil Cooler

transmission heat exchangerThe actual function of a transmission oil cooler is to remove excess heat from the transmission oil. Basically, oil is used in the transmission to reduce the friction that occurs when gears change position. And from what we know about friction, it can be reduced but not eliminated.

In addition, friction generates heat that needs to be dissipated. In a transmission oil cooler, this heat is channelled through the transmission oil. This oil moves from an outlet in the transmission to the radiator. The radiator uses a coolant to cool the oil as well as the water and returns it to the transmission.

There are two types of transmission coolers: one is the aforementioned radiator system, while the other is located in close proximity to the air conditioning condenser. Both coolers have the same effect and differ only in their practicality and operation. The correct oil temperature makes it easier for the transmission to work effectively. You can also have a heat exchanger between the coolant and the transmission oil.

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The good news is that if you have your car serviced as usual, including routine oil and filter changes, then your car’s oil cooler should last a very long time. But even regular maintenance cannot prevent a component from failing.

An oil cooler will show some symptoms before it fails completely. You just need to have the right knowledge to recognize these symptoms and take the right measures. Here we have listed some symptoms that may help you on your way.

1. There is an Oil Leak

One of the first signs you will notice before your oil cooler stops working is leaking oil. This leak can occur in many places. The oil can leak either near the transmission output, near the cooler connection, or at the rear of the transmission. The first two locations form a small puddle directly under the front of your vehicle. This leak is easily visible and can be detected every time you come back in the morning to start your car.

If the leak is located at the rear end of the transmission near the shaft, you may not be able to detect it easily. It is therefore advisable to always look for an oil spill immediately after you pull your car back from the driveway. Otherwise, you will keep damaging your transmission and end up paying for much more than just an oil cooler.

2. Noise While Shifting Through Gears

The oil inside the gearbox is necessary to maintain a healthy working environment for the gears. If the oil leaks or does not cool to operating temperature, your transmission may make a clunky noise every time you shift gears. When the oil is heated and reaches a very high temperature, it begins to boil and evaporate. This can cause the oil level in your gearbox to run out and eventually make it more difficult for the gears to shift effectively.

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Fortunately, you can feel a change when you shift gears. If it takes a lot of effort to shift a gear, especially a low gear, you may have transmission oil problems caused by a defective oil cooler.

3. Hose Damage

The oil cooler receives the transmission oil through a number of hoses which are connected between the transmission output and the oil cooler in the radiator. The hoses used for oil transfer are usually very stiff and tough, which means they can withstand high pressure.

In other words, they are not easily damaged. However, if they are damaged, they lose oil. If the oil does not reach the oil cooler in its entirety, it will not be cooled properly and the transmission will overheat.

4. Engine Overheats

If the transmission does not receive cool oil due to a defect in the oil cooler, your gears will not shift correctly. Improper shifting creates additional resistance that the engine has to overcome. This requires the engine to work harder than usual, and this causes the engine to overheat.

If you drive your car and experience slow gear changes and then find that your temperature reading is rising, take your car directly to a certified mechanic. A mechanic will have the appropriate remedy for your car problems.

Transmission Oil Cooler Replacement Cost

Each of these symptoms requires you to take your car to a professional mechanic. A mechanic will check your transmission oil and then check for leaks. If there are signs of oil cooler failure, you are advised to either decide to have the oil cooler repaired or consider replacing it.

Repairing the oil cooler is less expensive than replacing the oil cooler because replacing the oil cooler requires modifications to your radiator. The oil cooler is basically just a pipe that goes through the radiator. If it is worn, your mechanic will have to replace it with a new one, which will increase your labor costs. Typically, an oil cooler replacement will cost you about $100 to $200 with no labor cost. Depending on the amount of work the mechanic must do, you can expect labor costs of $100 or more.

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If you do not want to pay that much money, you should make it a habit to check all fluids in your car regularly and without fail. This simple exercise will help you make a diagnosis earlier and make the necessary repairs.

Hello I'm Magnus, the owner and the writer of this website. I have been working with cars since I was 16 and I'm specialized with in-depth Automotive diagnostics. Also been driving drifting for the last 6 years. I'm here to give you answers to all your automotive questions and I hope that you enjoy our content.

3 thoughts on “ Symptoms of a Failed or Bad Transmission Oil Cooler ”

  1. My vw one time had dirty brown oil mixed with the coolant and my mechanic straight blamed the gear box oil cooler and changed it. In about a week, same dirty oily mix in the coolant. I have decided to park and seek opinion first.
    So what causes oil to mix in the coolant, is it failing oil cooler or head gasket ?

  2. hello i have a vw mk4 1.6 sr edition germany 2003 when i go to the mountain suddenly my car decrease accelerate when i push fuel it doesnt accelerate what i want just the rpm go high and go slow and ma shifting gear take long to change and i smell something burned like oil burned i dont know. the next day when i go to work its doing fine my work its near my house some mechanic they said to me you have change the cooler oil for cooler air bc vw have this pro is this ok and thank u.

  3. I have stripped two Cat D8R transmissions from the same customer, and both had water mixed with the oil, and both pumps had seized, would this be due to a failed oil cooler?

  4. Due to a very high demand and high ammount of comments, you have to wait for some time for your car questions to get answered. If you want to get fast answers from a certified master technician you can ask your questions here:
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