In this guide, we’ll discuss how long can you drive with low transmission fluid. Transmission fluid is a viscous oil that keeps the gears lubricated and helps carry heat away from the internal components of the transmission.
The automatic transmission works on a hydraulic system, meaning that the clutches and bands are engaged by the pressure of transmission fluid when shifting gears. If the transmission is not using the transmission fluid or the transmission fluid is low, the gears will begin to grind, the clutches will slip and the transmission will overheat.
Driving with low transmission fluid is possible for about 10-30 miles with a 1-2 quarts deficiency, yet risky. It can cause jerky movements or prevent gear shifting. Always check the fluid level regularly, particularly if hard-driving or towing. Though generally changed after 30,000 miles, keeping transmission fluid optimal is vital as replacing a burnt transmission can cost over $5000.
Table of Contents
How To Check The Level Of A Transmission Fluid?
To check the level of transmission fluid:
- Park a car on level ground.
- Start the car to warm up the engine to an operating temperature as the minimum and maximum marks on the transmission oil dipstick are based on the transmission temperature of around 90ºC to 100ºC. The engine should not be run for more than 90 seconds to warm it up.
- With the engine running, depress the brake pedal and place the gear lever in each gear position, holding for approximately 5 seconds in each position. Then, put the gear lever in PARK.
- Turn off the engine.
- Remove the dipstick from the transmission and wipe it with a clean cloth.
- Insert the transmission dipstick all the way into the transmission.
- Remove the dipstick and check the transmission fluid level.
- If the level of transmission fluid is below the lower mark on the dipstick, it means that the transmission oil level is low.
Note: If the car has been driven for an extended period, at high highway speeds, in city traffic, during hot weather, or while towing a trailer, the transmission fluid must cool down to 90ºC to obtain an accurate reading.
The above-explained method to check the level if transmission fluid consists of general steps. Each vehicle has a certain method of checking the level of transmission fluid. So, you should always check the owner’s manual.
Can You Start A Vehicle With Low Transmission Fluid?
Yes, you can start your vehicle with a low transmission fluid but your vehicle will be jerky or rev high without moving.
Transmission fluid has the following main functions:
- Transfers power from the engine to the transmission (torque converter)
- Lubricates the gears in the drivetrain and prevents gears from grinding
- Prevents overheating of the transmission that is generated due to friction of gears and clutches
- Engages clutches and bands by applying a certain pressure and prevents slipping of the clutches
If transmission fluid is too low i.e. the transmission dipstick is bone dry, starting a vehicle with transmission fluid can damage the front pump (a pump that carries transmission fluid).
Moreover, if the transmission is dry and you continue to drive your vehicle, the transmission will overheat which will damage your engine. Moreover, as a rule of thumb, every 20-degree increase in the temperature of transmission above 175 degrees cuts the transmission fluid life by half.
In addition, low transmission fluid levels will cause the transmission to “lurch” when you engage gears or shift, or at times when you accelerate or brake. When low transmission fluid levels are combined with excessive heat and friction, transmission fluid may vaporize and form bubbles.
Bonus Read: Car jerks when shifting to reverse
What Happens If You Drive With Low Transmission?
Driving with a transmission fluid below manufacturer specifications can cause premature wear, and eventually lead to transmission failure.
While most transmission fluids are the same across the board, manufacturers typically specify a transmission fluid for a specific vehicle. It’s a bit like oil in your engine, only it affects the internal gears that connect your transmission.
Transmission fluid serves several purposes i.e. lubricating the gears, cooling the transmission, transferring power to the torque converter, and engaging the clutches with their optimum pressure.
If you drive with low transmission fluid:
- Transmission will not cool properly and will eventually burn up
- Clutches will wear out and slip due to insufficient lubrication
- The vehicle won’t move in any gear with the engine revving
- Gear shifting will be rough as there would be insufficient pressure applied to the clutches
What Are The Signs Of Low Transmission Fluid?
Transmission fluid acts as a lubricant and coolant to the transmission, an essential component to power up the transmission. There are multiple ways to tell if your transmission fluid reaches an insufficient level. When these symptoms occur it’s necessary to have it checked out immediately.
1. Delayed Gear Shifts
Low transmission fluid causes delayed gear shifts. When transmission fluid is low, it can’t generate enough pressure to engage the clutch, due to which delayed gear shifts occur. It also causes jerkiness in the vehicle as the gears are not shifted based on the demand of the vehicle’s speed.
2. Slipping Clutches
When the transmission fluid level drops below a certain level, it creates problems like slippage of the clutches, and there is not enough pressure to grip the clutches. Therefore, the gears do not shift as smoothly as usual. Moreover, low transmission can’t provide sufficient lubrication due to which clutch pad material wears out faster. As a result, the clutch can’t develop a sufficient grip to shift the gears.
3. Transmission Overheating
The transmission will run hotter than normal if the fluid level drops too low. If the fluid level is below the minimum amount required to lubricate the gears, the temperature of the fluid will increase due to friction and the vehicle may experience overheating issues.
When there is excessive overheating of transmission:
- Smoke will billow out of the transmission
- Transmission oil will oxidize and will form varnish-like substances. As a result, transmission oil life will decrease
- Metal parts of transmission will warp
- Sensors could damage
- Grinding noise from gears could be heard
Here is a universal chart that shows the relation between transmission operating temperature and the life of transmission fluid when the temperature of transmission goes above 175° F.
|Transmission Operating Temperature (°F)||Transmission Fluid Life (miles)|
Will A Light Come On For Low Transmission Fluid?
Check engine light and a flashing D (drive gear) light might come on for low transmission fluid. This is a warning signal that your transmission has a fluid leak or some other fluid issue. And if you continue to drive with low transmission fluid, the gears will start making an excessive grinding noise and the transmission will burn up.
If the flashing drive light or check engine light comes on, you should also check the transmission line pressure sensor/pressure switch, transmission pressure sensor, and solenoids in the valve body. Overheating of the transmission due to low transmission fluid could also damage the sensors. You can read my guide on transmission shifting hard to learn more.
You can use this OBD2 scan tool to pull related trouble codes.
How to Identify a Transmission Fluid Leak?
If there is a red fluid leaking under the transmission pan of your vehicle or you find spots of red fluid on the driveway, it indicates the leakage of transmission fluid. You could also see leakage of transmission fluid from the hoses going in and out of the transmission cooler. Moreover, if the seal of the gear pump in front of the torque converter is damaged, transmission fluid will also leak into the bell housing (a casing that encloses the torque converter and pump). You can read my guide on low transmission fluid without a leak to learn more.
Can I Just Add Transmission Fluid?
It depends on the condition of your transmission fluid. If the vehicle has been driven for less than 30,000 miles after the last transmission fluid service, you can just add transmission fluid without changing it. In these cases, when you see that the transmission fluid is sprayed all over the engine due to leakage and its condition is pretty fine, you can just add transmission fluid.
In cases when you have driven over 30,000 miles and the transmission fluid is dark brown and lumpy, you should change the transmission fluid and transmission filter.
Note: Transmission fluid filling requirements are different for a transmission flush and transmission change service. If you perform transmission flush, you are also changing the fluid in the torque converter in addition to the transmission pan. In transmission change service, you are just changing the transmission fluid in the transmission pan.