Finding and Fixing Leaks

Transmission Fluid Leaks

You can have a leak in both an automatic transmission or a manual one, but leaks in these different transmissions should be treated differently. The fluid colors are often different depending on which type of transmission you have.

Automatic Transmission Fluid Leaks

Automatic transmission fluid is usually red. In fact, I can’t think of an automatic transmission fluid that isn’t red, but I could be wrong. Come to think of it, I think Porsche uses some form of manual transmission fluid in some of their automatic transmissions. Let’s just say, for the most part, automatic transmission fluid is red. Consult your owners manual or service manual to be sure. Believe it or not, the red color is added to the fluid to give it its distinction. Before the dye is added, automatic transmission fluid looks much like motor oil. The dye is added to make the fluid more identifiable.

That said, it doesn’t always mean your automatic transmission fluid will appear red in color. As the fluid ages, it turns a darker red or dark brown. As a result, it can sometimes be confused with motor oil. For this reason, you might need to find the location of the leak to determine whether you have an automatic transmission fluid leak. Even then, it might not be conclusive. For instance, if you find a leak between the engine and transmission and it appears dark brown, you might think it’s an engine oil leak. In this instance it’s very difficult to tell. About the best method I can offer here is to use the recommendation for finding engine oil leaks with dye. You can put the dye in either the engine or transmission and then run it for a while. If you see the dye show up under florescent light, then you know the component you put the dye in is the one that’s leaking. Either way, you’re likely going to have to remove the transmission to repair the leak.

Knowing that this is likely, you might just go ahead and remove the transmission to inspect for the source of the leaks. Sometimes it’s like a Band-Aid: It might be easier to just rip it off instead of removing it slowly. Less pain that way.

Automatic transmission fluid leaks can be debilitating. The automatic transmission is dependent on the fluid within it to operate properly. If enough fluid leaks out, it can cause shifting issues or even transmission damage. This means that if you have a leaking automatic transmission, it should be addressed sooner rather than later. Until you can fix the leak, do what you can to keep the fluid topped off.

Another concern is automatic transmission fluid leaking onto the exhaust. Automatic transmission fluid can be more flammable than other fluids. For this reason, if you have an automatic transmission fluid leak that’s getting onto the exhaust, repair it sooner rather than later to help eliminate the possibility of fire.

You might not always find an automatic transmission fluid leak at the transmission. Cooler lines often run from the transmission to the radiator or external cooler. If this is the case, be sure to check these areas for the source of your leak. In addition, if the cooler is part of the radiator assembly, transmission fluid can get into the cooling system and coolant can get into the transmission. Neither is good. When automatic transmission fluid mixes with coolant, it usually gets milky and frothy. So if you see this on the dipstick, check the cooling system to see if it’s contaminated as well.

One other note on automatic transmissions. You might not find a dipstick on your transmission. If this is the case, don’t be alarmed. Many new transmissions are made this way. You can still check the fluid level on most of these, but it often requires that you raise the vehicle and remove an inspection plug. Consult your service manual for the procedure on your vehicle.

Manual Transmission Fluid Leaks

This is where it can get tricky. Most manual transmission fluid is the same color as motor oil. However, sometimes manual transmissions use automatic transmission fluid. This can be confusing if you’re trying to find a leak in your manual transmission. Once again, you can use dye to help you find the source. If you put the dye in either the engine or transmission, you can then use that information to nail down which one is leaking.

To be honest, I don’t often see leaks with manual transmissions. That’s not to say they don’t leak; leaks just don’t seem to be as prevalent. Normally what I do find are the occasional axle seal leaks. For the most part, manual transmissions give me less trouble. In addition, clutches are serviceable items. This means that you need to remove the transmission periodically to service the clutch. When doing this, it’s a good idea to inspect for leaks and repair them while the transmission is removed from the vehicle. It’s also not a bad idea to inspect the engine’s rear main seal as well as the back of the cylinder block for leaks when performing a clutch service. There’s no better time to address leaks than when you have the transmission removed from the vehicle. Be sure to check your owner’s manual or service manual to find out what type of transmission fluid your transmission is supposed to take. I’ve seen countless manual transmission problems as a result of not using the correct fluid. As I said, there are a lot of different types of manual transmission fluids. Using the correct one will ensure a long and fruitful life for your manual transmission.

As with the other leaks, stop leak products are not recommended for the same reasons listed above.

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