Your car’s transmission is one of the most hardworking yet most neglected components. Very few car owners think of checking transmission fluid levels let alone replacing it.
This behavior is cultivated by the notion that transmissions and their fluid can last for a lifetime. Well. Manufacturers say this, but their definition of life isn’t similar to what car owners have in mind.
Most manufacturers define a car’s lifetime as the mileage or years they are willing to issue warranties for a car.
For instance, if your car gets a five-year or 100K miles warranty, the manufacturer believes that to be the car’s lifetime.
We all know cars last way longer than this.
Most industry specialists recommend changing transmission fluid every 30,000 to 60,000 miles. If you push your car harder by carrying heavy loads, towing, or driving in start-stop urban traffic, you should change your fluid more often.
What Does Transmission Servicing Entail?
A couple of things goes into servicing your transmission. This depends on how many miles you’ve put into your transmission and what you want to overhaul.
It doesn’t matter whether it is an automatic or a manual transmission. The servicing is more or less the same.
Transmission Fluid Exchange
This is the most common transmission servicing procedure for car owners. It is as simple as replacing your car’s engine oil.
All the mechanic has to do is open the drain valve at the bottom of the transmission pan to drain the old fluid.
After this, they use a funnel to fill up the transmission with the manufacturer-specific transmission fluid.
You will need a funnel that fits in the transmission fluid dipstick pipe as there is no bigger opening to fill up the transmission through.
Ensure that you use your manufacturer-specific transmission fluid. This information is often printed onto the transmission fluid dipstick’s handle.
Transmission Filter Replacement
Over time, the metal shavings created when gears change in the transmission fill up the transmission fluid filter screen.
This could impair the flow of the fluid. To avoid this, you have to open up the transmission fuel sump.
Can You Clean and Reuse a Transmission Filter?
Yes. You can clean transmission filters. In most cases, they are wire screens. If you can still see some bit of the mesh in your filter, you can clean it out until it is clear of debris again.
However, transmission fluid cleaners are cheap. If your’s is too clogged or already looks old, it will do no harm to buy a replacement. Ensure it is of the same quality as the original or you will be changing it sooner.
How to Clean Transmission Fluid Filter
Once you open the transmission oil sump, you will see the filter. If it is not too dirty, you can clean it in place and rinse off the residue. If it is very dirty, follow these steps.
- Disassemble the filter carefully. Note how the different parts go in so that you can reassemble it correctly
- If the filter is held on by crimps, use a bench grinder to cut free the filter
- Drill through the mounting hole crimps to separate the different halves of the filter
- Hold the fluid filter pieces over a pan. Spray them with disc brake cleaner and use a toothbrush to carefully brush off stuck pieces
- Don’t be too vigorous. You could damage the fine mesh when overenthusiastic
- Carefully file clean the filter edges
- Reassemble the pieces in order and use new crimping metal to reinstall them in place
Most people opt to clean their transmission fluid filter in place and avoid the extra hassle of removing it. While this is a bit inefficient, it’s still better than driving around with a dirty and clogged transmission fluid filter.
What Happens if Transmission Filter is Dirty?
A dirty transmission fluid filter will interfere with the flow of your transmission fluid. It will make your transmission work harder and exhibits some tell-tale signs.
How Do I Know if My Transmission Filter is Clogged?
Here are some common signs to be on the lookout for. They could indicate that your transmission fluid filter is faulty.
Your Car is Slipping Gears
This is common in automatic transmission vehicles. The gearbox uses transmission fluid pressure to switch gears.
If your filter is clogged, it will interfere with fluid flow and make the car hit desired pressure to swap gears slower.
This will make it feel as if gears are slipping and not engaging completely.
If the problem is very serious, your car won’t engage gears at all. It will be undrivable.
Whirs and Whines
Your car might also make abnormal whirring or whining noises. The engine will sound as if it is revving up between gears if you are driving a manual. The noises will be more prominent.
If it is an automatic car, you should expect a very high-pitched whine. You will notice it more when you shift between park, drive, and reverse.
Normally, your car should shift smoothly. If you get any grating sounds when shifting, chances are that something is faulty. This could be anything including a clogged transmission fluid filter.
Transmission Fluid Leaks
A clogged filter increases the pressure in the system and also prevents your transmission fluid from being at the right place at the right time.
If this happens, chances are the fluid will either leak through old gaskets or even out through the vent tube.
Losing transmission fluid is never good news. Always have your transmission system serviced if you notice some leaks.
Check out the section of this article on signs that you’re losing transmission fluid for more on this.
A Burning Smell
Since your transmission fluid also cools the transmission, you’ll most probably smell the burning transmission before you notice any other symptom.
A clogged filter starves the transmission. This keeps the flow of fluid over the transmission slower. Your car’s transmission will quickly heat up and start burning.
If your transmission has a temperature monitor, it will send a transmission overheat warning and most probably put the transmission in limp mode to prevent further damage.
Having Trouble When Changing Gears
This is the same feel as slipping gears in an automatic transmission. Your car will feel uncertain when selecting gears and won’t shift as fast as it used to.
In a manual transmission, your gears will grind even if you still depress the clutch fully. However, this could also mean you have a worn out clutch, bad gears, or faulty transmission synchronizers.
Your Car is Noisier When in Neutral
Another sign that you have a clogged transmission filter is if your car makes abnormal noises when in neutral and at a standstill.
A good car should be very silent in neutral – unless the AC is on. The only noise you should hear is the steady hum of your engine idling away.
Any extra noise could mean trouble.
You Will Need Multiple Symptoms to Narrow Down
Frankly, all the above symptoms could point to different problems. You will need combined observation to deduce that your transmission filter is the problem.
Follow these steps to narrow down.
- Check your transmission fluid levels. If they are below the recommended level, changes are topping up could fix the problem
- Check your transmission fluid pan for any leaks
- If you recently changed the transmission fluid and it doesn’t seem to be leaking, look into other problems – especially if you cleaned/replaced the filter too
It’s always good practice to service the entire transmission instead of just changing the fluid. This means you should
- Clean up the transmission fluid filter
- Install the transmission pan with a new gasket after examining it for damage
- Refill the transmission with new transmission oil
How to Tell if Your Transmission is Leaking Fluid
Another thing that could push you into servicing your transmission is finding out that it is leaking.
With other fluids like coolant and engine oil leaks possible, knowing how to identify and differentiate a transmission fluid leak is crucial.
If your transmission fluid leaks, you will get symptoms similar to what we discussed in the clogged filter section.
Here are some additional things to check when doing a routine car fluids check. It will help you identify and sort out a transmission fluid leak on time.
Keep Checking the Dipstick Levels
A leak will definitely lead to a transmission fluid level drop. Note that manual transmissions don’t have dipsticks. The oil is pre-filled and will only be replaced if you service the transmission.
- Pull out the dipstick from its pipe in the transmission
- Wipe it clean and reinsert it into the transmission
- Wait for a few seconds and pull it out
- The level should be at the Max or near it. If it is slightly below or way below the minimum level, you have a problem
If your transmission fluid level is slightly low, there is no problem in topping up as long as you use the right transmission fluid.
Be careful when topping up and only add very little at a time. Removing excess transmission fluid is hard.
You should, however, get your transmission checked if:
- You noticed leaks below the car that could be transmission fluid
- You have to top up more than a quart of fluid
- You are topping up transmission fluid regularly
A Dashboard Warning Light
Some modern cars don’t have a dipstick or have a dipstick and a transmission fluid level sensor.
If this is the case, you will get a warning on your dashboard once your transmission fluid levels are low.
Fluid Leak Under the Car
The last sign to be on the lookout for is a pool of fluid beneath your car after parking for a while. Transmission fluid leaves dark spots on the floor.
In most cases, you will find a puddle of red and slick liquid at the front middle part of your car’s parking. Checking beneath the transmission could reveal a trail of the leaking fluid.
If you are not sure, you could confirm by checking the transmission fluid and oil levels. If the oil level is steady and the transmission levels are dropping, then you have your culprit.
Is it OK to Drive With a Transmission Leak?
Even though driving with a transmission fluid leak isn’t necessarily life-threatening, it could cause expensive damage to your transmission.
Transmission replacements are expensive. Park your car and have an expert look at and fix it before you can start driving again.
Is it Expensive to Fix a Transmission Leak?
The cost varies depending on what caused the leak and if further damage has happened to the transmission.
You could be looking at as low as $40 to something as high as $1000. Moreover, if the leak went unnoticed for a while, there could be more internal damage that is expensive to fix or calls for a completely new transmission.
Is it Better to Flush or Drain Transmission Fluid?
Most people argue that a traditional transmission fluid swap using the drain plug only replaces around 70% of your transmission fluid.
The remaining 30%, they argue, will contaminate the new fluid. While this is true, manufacturers accounted for this when coming up with the recommended service schedule.
Flushing your system forces more fluid out making you replace more. This is unnecessary if you will still stick to the regular servicing schedule. It could also have potential problems like:
- A flush could force loose metal particles back into the transmission
- The unexpected pressure could damage aging but otherwise fine gaskets
- If some of the fluid leaks on parts like the clutch, it will make it slip more
Flushing your transmission is normally unnecessary. Save your money and stick to servicing your transmission more often if you want it to stay healthy for longer.
What Happens if You Use the Wrong Transmission Fluid?
Mixing transmission fluids is not okay. Only stick to what the manufacturer demands for. The wrong transmission fluid could lead to:
- Poor lubrication
- Overheating
- Transmission failure
- A voided warranty
- Erratic gear shifts
What Should I Do If I Use the Wrong Transmission Fluid?
Stop driving your car as soon as you realize or suspect that you used the wrong transmission fluid. This will mitigate damage and ensure that repairs won’t be as costly.
If you are lucky enough to have noticed before driving a couple of miles, the remedy could be as simple as draining the wrong fluid and adding a fresh batch.
Note that you might have to drain twice in quick succession (or flush the system) to get rid of as much of the errand fluid as possible.
If you had already driven some distance, have an expert mechanic check your system. They will help you determine if the transmission can be saved or has been damaged beyond repair.
Should I Check Transmission Fluid When Cold or Warm?
It’s best to check transmission fluid levels when your car is up to operating temperature. Since the fluid expands when the car warms up, checking it on a cold engine could give you a false low.
Also, topping up on a very cold engine could have you overfill the transmission fluid reservoir.
What Happens When You Overfill Your Transmission Fluid?
Just like the case with oil and coolant, overfilling your transmission fluid is never a good idea. It could lead to a couple of problems like:
- Overheating
- Pressure build up
- Excessive transmission wear
- Eventual transmission failure
Signs That You Overfilled Your Transmission
High Levels on Your Dipstick
Your dipstick is your ally when checking fluid levels. They’ll tell when it’s time to refill or if you have too much.
Follow the normal procedure to check the transmission fluid levels. If the fluid is above the MAX level, then you have more fluid than you need.
Leaking Fluid
Excessive transmission fluid forces the transmission to work at higher pressures than it was designed to.
In most cases, this will make it easier for the fluid to leak around gaskets and the drain valve leading to a transmission fluid leak.
Weird Noises
Any humming, grinding, or whining is a bad sign. Your transmission shouldn’t make noise that overpowers the engine.
Your transmission will whine when you overfill and grind when the transmission fluid levels are too low.
Issues Changing Gears
Since too much fluid causes pressure to build up, it could also encourage foams to appear in the coolant.
This affects its efficiency making it harder for gears to shift smoothly.
How to Fix an Overfilled Transmission
Your only hope to remedy an overfilled transmission is draining the excess fluid. While some people try siphoning, this is often complicated as the transmission fluid sump isn’t as easily accessed as the oil sump.
The easiest way is to slightly open the drain port under the transmission and let out some fluid.
Remember to get a pan to catch the draining fluid.
You will also need extra fresh fluid to top up the transmission should you drain it below the ideal level.
Remember to take all your transmission fluid level readings while parked on level ground and on a car that has warmed up to normal operating temperature.
Bottom Line
Servicing your transmission frequently will keep it operating at its optimum. It might be an additional cost but it will extend your transmission’s lifespan. It is especially important if you own a second-hand vehicle that is beyond its manufacturer’s warranty.