Heat is the number one cause of premature transmission failure. Not manufacturer errors, or even defective parts. It accounts for approximately 90% of all automatic transmission failures.
In This Guide
- How Automatic Transmission Fluid Cools a Transmission
- Transmission Fluid Life Expectancy vs Temperature
- Fluid Temperature & Damage
- How to Prevent Transmission Overheating
- When to Install a Transmission Cooler
- Other Transmission Heat Sources
Excessive transmission heat is responsible for the start of many transmission problems including; ruptured seals, cracked gears, slipping transmission bands, failed bearings, inoperable solenoids, and delayed clutch engagement. You name the part, and too much heat can cause it to break.
This silent killer has claimed the service life of countless transmissions, and it could be wreaking havoc on your vehicle every time you put it in gear. An overheated transmission can often go unnoticed until it’s too late and something breaks.
The most common causes of overheating include solenoid problems, transmission fluid leaks, low fluid levels and burnt/old fluid. Other heat generating factors are if you live in a hot climate, often drive in stop and go traffic and/or tow heavy loads with your vehicle.
How Automatic Transmission Fluid Cools a Transmission
Transmission fluid contains chemical additives that provide lubrication and the fluid pressure to change gears, but its primary function is heat removal. The spinning gears, expanding springs, and whirring turbines that make up a transmission generate friction as they move about.
This friction produces a lot of heat, which can cause stress fractures, varnishing and other forms of damage to the internal components if it isn’t dealt with quickly.
For this reason, automatic transmission fluid (ATF) is formulated to absorb the heat as it flows through the moving parts. It then carries the heat out of the transmission to the radiator, where the hot fluid is forced through a special cooling chamber that uses aluminum fins to extract heat from the ATF.
As air flows through the radiator, the heat is dissipated and the cooled transmission fluid is then piped back to the transmission for another round. If the fluid isn’t able to remove and expel heat through the factory transmission cooler fast enough, the transmission will overheat and damage will start to set in.
Transmission Fluid Life Expectancy vs Temperature
Over time, heat breaks down the organic compounds inside transmission fluid, causing it to take on a darker red, then brown, then black color. It also becomes thinner, which significantly reduces the amount of heat that it’s able to carry away from the moving parts.
If a transmission isn’t serviced (new fluid + filter) every 20,000 to 30,000 miles or once every 12-18 months, the fluid will become ineffective, and the normal operating temperature will increase.
The ideal operating temperature of transmission fluid is 175 degrees. Overheating occurs after the temperature surpasses 200 degrees, and the failure rate doubles for every additional 20 degree increase after that.
So if you drive the vehicle with the fluid temperature at 240 degrees, your transmission will develop significant problems and fail 4 times sooner that it would have otherwise. Fresh, clean fluid on the other hand, will make it run cooler, shift better, and last longer.
Fluid Temperature & Damage
- 220-degrees = varnish forms on metal surfaces
- 240-degrees = seals harden
- 260-degrees = transmission bands and clutches begin to slip
- 295 degrees = seals and clutches burn – call a tow truck
For every 20 degree reduction in fluid temperature, your transmission’s lifespan will approximately double!
Low transmission fluid levels will also cause the transmission to overheat, rather quickly. Without enough ATF to remove the heat, the temperature can skyrocket past 260-degrees, resulting in a slipping transmission, along with serious damage to the clutches, bands, and torque converter.
To keep this from happening, check your transmission fluid level once a month, or every two weeks if you spend a lot of time on the road. And don’t forget to leave the motor running when you check the transmission fluid, otherwise you won’t get an accurate reading.
How to Prevent Transmission Overheating
You should check your vehicle’s fluid at least once a month in order to spot issues such as a low fluid level or worn out dirty/burnt fluid. This will allow you to fix these early warning signs before they cause serious transmission problems that can damage or destroy your transmission.
In addition to checking the level and quality of fluid using the dipstick, be sure to look under your car occasionally for stains on the driveway or transmission pan to make sure that your fluid isn’t leaking.
Your vehicle’s transmission fluid should be changed every 30,000 to 60,000 miles. You can change the fluid yourself or have a transmission shop flush the fluid from your vehicle.
If you drive in a hot climate, a lot of stop and go traffic or haul heavy loads, the fluid should be changed more often than the suggested range – every 15,000 to 20,000 miles for example. That way your transmission is always running on fresh, effective fluid that will keep it cool.
3) Add an External Cooling System
Your vehicle’s radiator is responsible for cooling down the transmission fluid, so be sure to change the coolant inside it every 2 years or so.
If you haul or tow heavy loads, the radiator alone may not be enough to keep the fluid cool and you should consider installing an external transmission cooler. A stacked plate cooler for example is easy to install and attaches to the front of the radiator.
4) Add a Deep Pan
If your transmission has overheated, then it is worth considering adding a deep pan. A deep pan allows you to add more transmission fluid to your vehicle, which helps spread out the heat and remove it from the transmission faster. Aluminum pans dissipate heat better than those made of steel.
When to Install a Transmission Cooler
Towing causes a serious amount of strain/heat buildup. So does the constant up-down shifting the occurs when you’re crawling through traffic, or driving in hilly/mountainous terrain.
If you regularly do this type of driving, then you need to seriously consider having an aftermarket transmission cooler installed. Most are designed to work in tandem with the manufacturer’s original transmission cooler, and they provide increased fluid capacity so that more heat will be removed, faster. To keep your transmission temperature from exceeding safe levels, this is the best way to go.
Other Transmission Heat Sources
Worn transmission bands, clutches, and solenoids can also cause your transmission to overheat. If the part isn’t functioning correctly, it can generate excess friction heat and overwhelm the transmission fluid.
Even though just one part is worn or broken, the high temperature can do things like warp the valve body, and destroy the torque converter internals. So if you can help it, try not to drive the vehicle until the transmission is repaired.
What to Read Next
- Common Transmission Problems
- What is a Transmission Flush?
- How to Check Transmission Fluid
- How to Change Transmission Fluid
- Transmission Solenoid: Common Problems
Over to You
We’re interested to know – has your transmission overheated? If so, how did you fix it? Let us know by leaving a comment below!