The fluid in your transmission is as vital as your vehicle's engine oil. If you've noticed your transmission fluid is running low and are wondering if it's because of reasons other than a leak, we can help. We researched several professional sources to find out the cause.
A vehicle will lose transmission fluid only when there's a leak. Because there is no combustion with this fluid, it cannot burn off or evaporate while in an air-tight space. If you are running low on this fluid, it is because of a leak. You can trace the leak to many points including:
- Faulty transmission pan gasket
- Corroded transmission pan
- Leaking transmission drain plug
- Damaged transmission pan
- Transmission fluid pipe
- Clogged transmission ventilation
Now that we know that the only way to lose transmission fluid is through a leak, we'll look into where these leaks occur. You might also have questions about the best way to add transmission fluid or how to tell when this fluid is low. Keep reading to get the details.
Can Transmission Fluid Evaporate?
Earlier, we discussed that transmission fluid will only leave your vehicle through a leak. This fluid will not evaporate or burn off. But, there are multiple places where a leak can happen. Let's look at where this is most likely to take place.
1. Faulty transmission pan gasket
The transmission fluid is stored underneath your vehicle in a thin steel pan that is fixed in place and sealed with a rubber gasket. Over time, gaskets can wear out or corrode.
A faulty transmission gasket is the first thing you should look for if you notice you are leaking transmission fluid.
When you remove the transmission pan, you can better inspect the gasket. We recommend that anytime you remove the pan, the gasket should get replaced. There's a chance that, if someone removed it before, they didn't affix a new gasket to the pan.
If you see signs of damage to the gasket, replace it and your transmission leak should be solved.
2. Corroded transmission pan
Sometimes, the leak comes from the transmission pan itself. Typically, these are steel, but they get exposed to a lot of harsh elements. Those who drive in snowy and icy conditions might discover their pans get corroded over time due to salt on the roadways.
If you have an older vehicle, rust may have eaten through holes in the transmission pan. If you notice rust anywhere on the pan, replace it.
Some pans are aluminum. This material is nowhere as strong as steel. A rock bouncing off the pan from the road can dent or crack the pan. If you notice dents or damage to the pan, it's time to replace it.
3. Leaking transmission pan drain plug
If your transmission pan has a drain plug, there might be fluid leaking from there. If the pan and gasket are in great shape, carefully check the plug. When you or someone else changed the fluid in the past, a new O-ring might not have gotten installed.
The O-ring seals between the plug and the pan. Every time you drain fluid out of the pan, it should get replaced. This could very well be the source of the leak if the ring becomes cracked or worn.
4. Damaged transmission pan
Whether your transmission pan is steel or aluminum, it might received some damage the last time it was removed. Technicians will often use a flat-blade screwdriver to pop the pan away from the vehicle.
Sometimes, if someone uses too much force, the pan gets bent. Inspect the edge of the transmission pan to see if it has a bend. Should you notice any spot where the seal isn't firm, that is the likely source of your leak.
5. Transmission fluid pipe
Most transmissions will have a transmission cooling line. Over time, this line can also become damaged or corroded. If your transmission pan and its rings and seals are in great shape, there's a good chance the problem is with this line.
Carefully inspect the fluid pipe from the transmission pan all the way up to the transmission cooler. Any holes, cracks, or otherwise damaged areas indicate that the fluid pipe requires replacement.
6. Clogged transmission ventilation
Most transmissions have a ventilation system. Usually, this is located at the top of the transmission itself. When it becomes clogged, it can make for some pretty messy leaks.
If you have exhausted all possibilities that we mentioned earlier, take your vehicle to a trusted mechanic. Ask if your transmission has a ventilation system. If it does, have them inspect it.
This area of a transmission is rather difficult to reach. We recommend letting a professional take over at this point, as you will need them to diagnose this as a cause and to fix the problem.
What Are Signs That My Transmission Fluid Is Low?
Aside from leaks, there are some signs that your transmission fluid is low. If you notice any of the following while you are driving, check your transmission fluid levels as soon as possible.
If you have a manual transmission, you might notice that you have trouble shifting from one gear to the next. Whether you are shifting up or down if you have difficulty getting the shifter into position, this should warrant your attention.
A slipping transmission can mean that your transmission needs serviced or replaced. But it can also mean that the fluid is low from leakage.
A grinding sound is another sign to be aware of. You'll likely hear this whenever you try to shift manually, or when you accelerate if driving an automatic.
Transmission fluid works as a lubricant, cooling off the transmission as it works. Low fluid will create metal-on-metal friction between the moving parts, resulting in the grinding sounds.
Dark transmission fluid
If you are driving an older vehicle, check the color of the fluid. Transmission fluid will turn darker over time, but will also darken faster if it is low. Contaminated transmission fluid will also darken.
Should the fluid be dark, have your vehicle thoroughly checked out for transmission fluid leaks. Once the leak is located and fixed, ensure the fluid gets replaced.
For manual transmissions, the feel of the clutch may indicate a low level of transmission fluid. When the fluid is low in the line, it won't have the amount of pressure it needs for the clutch to work properly.
So, this results in a soft or 'spongy' feel when pressing down the clutch while shifting.
How Do You Add Transmission Fluid?
If you find you need to add transmission fluid to your vehicle, it is easy to do with most vehicles. Keep in mind, some trucks might require a bolt to be removed from the transmission to check the fluid.
If that's the case, these steps do not apply to you and you should have a trained technician show you how to check and add the fluid.
- Park your car on a level spot and apply the emergency brake. Check your owner's manual to see if you need to leave your vehicle running, or if it will suffice to just have the engine warmed.
- Locate the transmission dipstick. It will be orange or yellow, usually. Just don't confuse it with the oil dipstick!
- Pull it out and wipe it clean of fluid with a shop towel or rag.
- Reinsert the dipstick and pull it out again. The fluid should be between two hatch marks. If it is below the bottom one, then your fluid is too low. If it is, follow steps five through eight.
- Place a funnel where the dipstick goes. Be sure that the tip is fully inserted before you go to the next step.
- Slowly pour the fluid in small amounts. Only add a bit at a time. You can always add more fluid, but it's really hard to remove it should you overpour. So, pour slowly, and only a small amount at a time!
- Check the level again. You should check the level after each pour so that you don't overfill.
- Repeat steps six and seven if necessary.
How Far Can I Drive On Low Transmission Fluid?
If you are aware that you have low transmission fluid, add it as soon as possible. Should you have a slow leak, it's best to always carry transmission fluid with you.
We recommend getting any leak identified and fixed as soon as possible. We also don't recommend driving far when your fluid is low. Slow leaks can become major ones in an instant.
Driving on low transmission fluid is a risk. If you run too low, the transmission will overheat. And, doing this will probably result in needing to get the entire part replaced, which isn't cheap.
Transmission fluid will only leave your vehicle through a leak, which could occur in several places. Modern vehicles won't need their transmission fluid changed until at least 100,000 miles unless you do a lot of heavy towing.
It's best to keep this vital fluid up to the fill line so that you don't damage the transmission. Drive safe!
If you found this post on transmission fluid helpful, we think you'll get a lot of great information out of the following automotive posts:
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