The vehicle’s transmission is the second most crucial part of the drivetrain after the engine; it is a torque multiplier by gearing down the engine to pull away easier and gear up so the engine can cruise at an optimal RPM and save fuel.
When there is too little oil, it can cause damage to the transmission and driveline, so what are the low transmission fluid symptoms?
- Transmission Slipping
- Transmission Whining
- Transmission Overheating
- Delay In Gear Changes
- Erratic Shifting
- Transmission Unable To Shift
- Transmission Failure
With the symptoms listed, let us go more in-depth into each one.
7 Low Transmission Fluid Symptoms
1. Transmission Slipping
On automatic vehicles, when it is too little or no oil in the transmission, automatic cars can start slipping.
The engine RPMs will rise, but the vehicle won’t accelerate as intended, as if the transmission isn’t connected to the differentials.
Since everything in the automatic gearbox is wet, lubricated by the transmission oil, when it starts running dry, it will wear out the wet clutches like those fitted in dual-clutch transmissions and solenoids controlling the flow to and from the torque converter on typical automatics.
If these parts fail, the automatic transmission starts slipping.
2. Transmission Whining
When there is low or no oil in both automatic and manual transmission, the gears inside will start whining or hum as the lubrication dissipates.
It starts whining because the friction between the gears increases as the transmission oil gets worked out between them.
Here is an excellent example from @tte_si1866 demonstrating gearbox whine in his Audi:
3. Transmission Overheating
As mentioned above, as the gears in the gearbox aren’t sufficiently lubricated anymore, they will start humming or whining and generate a lot of heat.
In an automatic vehicle, the transmission overheats icon will appear on the instrument cluster.
If a manual transmission vehicle is 4wd, 4×4, or rear-wheel drive, you will feel the heat radiating from the transmission tunnel and gear lever.
At this point, the lack of oil will do significant mechanical damage to the transmission.
4. Delay In Gear Changes
The delay in gear changes is typical with automatic transmission vehicles with too little or no oil.
The whole transmission is controlled with the transmission fluid, solenoids will push oil to gear selectors to engage and de-engage gears, so if there is low oil, it will take much longer to pressurize the solenoid.
This insufficient pressure in the solenoids causes the gear changes to take longer.
5. Erratic Shifting
The shift delay caused by low oil in the transmission can also cause the automatic transmission to hunt and miss a shift.
The car will hesitate and do weird shifting while driving; some cars will gear down, others will gear up, and some might even engage neutral as a safety to protect the transmission.
6. Transmission Unable To Shift
On a manual transmission, the gear shifts will start getting harder and harder as the synchromesh starts breaking or seizing up to the point where you won’t be able to shift anymore.
Another issue that can start is the gear lever will jump out of gear as the shift rod and fork start wearing out.
On automatic transmissions, when there is little to no oil, the gearbox won’t be able to shift gears anymore.
7. Transmission Failure
When all of the above symptoms are ignored, there will come the point where the transmission will just fail; it can be a catastrophic failure that can put you in danger of losing control of the vehicle.
The gearbox will seize up, and it can either break a part of the gearbox, usually the tail portion, or lock up the entire driveline and cause the vehicle to lose traction.
When the tail portion of the transmission breaks off in a 4wd, 4×4, or RWD car, it can cause the driveshaft to piledrive itself into the ground and even flip the car in the process.
Here is a Ford Mustang drag car where the driveshaft stuck into the track and almost flipped the car, and broke off the rear suspension:
Final Thoughts On Low Transmission Fluid Symptoms
If you suspect that your vehicle has too little oil in the transmission, have it checked, or if you know how to check it yourself, please do so.
Replacing or rebuilding a transmission can cost just as much as rebuilding an engine, and it can get pricey.
Hopefully, you found this article helpful and will help you keep your car on the road for longer and give you many trouble-free miles.
FAQs
What Happens When Transmission Fluid Is Low?
In both manual and automatic transmissions running too low in transmission fluid will cause the gearbox to overheat, as the transmissions also use oil for cooling.
In automatics, the transmission will also start slipping, while in manual transmission, it will get harder to put it in gear.
What Does It Sound Like When Transmission Fluid Is Low?
The transmission will start humming or whining as the gears inside start running dry, and the friction between them increases.
Can I Just Add Transmission Fluid?
When you react quickly and don’t drive the vehicle any further when you realize there is too little oil in the transmission, you can add oil, and there will be no consequences.
If you keep driving and it is at the point where the transmission is overheating or whining, topping it up won’t fix it, as something inside the transmission has already failed.