Transmission overheating can be a double whammy. Not only does a hot transmission perform poorly, but when the transmission fluid is heated beyond 240 degrees, it starts to break down, losing its lubricating properties. This can cause even more heat from friction and risk grinding the gears and damaging other moving parts.
If you’re noticing signs of your transmission overheating, such as hot smells, gears slipping, or getting stuck in gear, you must pull over to cool the transmission down as fast as possible.
The more you drive with an overheating transmission, the more you risk serious damage to both the engine and the transmission. So, knowing how to cool down and care for your transmission when the temperature inside starts to rise can save you a lot of money.
If your engine temperature gauge is climbing toward the redline or you notice potential signs that the transmission is overheating, you should pull off to the side of the road as soon as possible to let the engine and transmission cool down.
While sitting on the shoulder, you’ll have some time to consider why the transmission started overheating in the first place and what you can do to keep it from happening once you get back on the road.
What Are the Signs of an Overheating Transmission
Signs that your transmission is overheating and needs to be cooled down can sometimes start out subtle. Such as the transmission hesitating to change up or the engine revs too high when braking. As the transmission gets hotter, you might find it getting stuck in gear or slipping into neutral. Depending on the severe overheating, you might also notice strange smells like burning plastic and possibly even a check engine or transmission light.
1. Engine Revs Too High When Braking
An overheating transmission can make it hard for the torque converter and the TCM to effectively downshift the transmission. The engine revs too high before shifting down and might catch the next gear hard.
2. Hesitated Gear Changes
Hesitating gear chances is one of the more obvious signs of an overheating transmission that can cause delayed gear changes or erratic shifting. At this point, the transmission is either overheating or about to overheat, and you need to cool it down as soon as possible.
3. Transmission Slips Into Neutral
An overheated transmission can slip into neutral unexpectedly or get stuck in neutral. This could also be due to low transmission fluid where there isn’t enough fluid to keep it in first gear. The low pressure lets the fluid drain back into the pan, where the filter can pick it up again, and suddenly you can get it back into first gear. Only to have the problem recur.
4. Burning Plastic Odors
When a transmission starts getting dangerously hot, it will begin to give off odors like burning plastic or melting wires. If your heating is set to fresh air, you might even notice them coming through the dash vents. This might also be the transmission telling you that the fluid itself is starting to break down, and you need to cool it down fast or risk running on bad transmission fluid for the rest of the drive.
5. The Car Grinds or Vibrates When Accelerating
Degraded transmission fluid with poor lubrication caused by an overheating transmission can cause gears to grind as you accelerate. This might feel like shuddering, jerking, or vibrating when you step on the accelerator.
6. The Check Engine or Check Transmission Light Comes On
The way overheating affects transmission performance can eventually cross a threshold that causes the ECU or the TCM to turn on the check engine or check transmission warning light. When it does, the car’s computer will throw a code.
Code P0218 is the blanket code for Transmission Over Temperature. This could be due to a stuck solenoid, low transmission fluid, or other mechanical faults. No matter what, you need to pull over immediately to let the transmission cool down.
Codes P0750 thru P0770 indicate a transmission solenoid failure, which might also prevent transmission fluid from circulating through the radiator. Even if the transmission hasn’t overheated already, it’s likely about to, and you need to cool it down fast.
7. Limp Home Mode
In newer cars, the performance issues caused by an overheating transmission can cause the car’s computer to activate the limp home mode. This will limit your gear range to one or two gears and govern the engine’s RPMs to prevent further damage.
What To Do When Your Transmission Overheats
If you’re noticing signs of an overheating transmission or have a transmission temperature gauge telling you it’s running too hot, you must pull over as soon as possible. Then the following steps can help you cool down the transmission as fast as possible.
Some leaks are more active when the vehicle is moving, recently stopped, or the transmission is hot. If you see a leak, note it and take a picture with your phone.
The engine radiator helps cool the transmission, and if it has a problem, your transmission will likely overheat again, even once you get it cooled down.
The fluid on the dipstick should be near the HOT line. The fluid should be a semi-translucent pink color.
If the transmission fluid is near the low or COLD line on the dipstick, your overheating is likely caused by low transmission fluid. This is usually related to a previously unknown leak.
If the fluid on the dipstick is dark or turning brown, the overheating causes it to degrade, losing or losing most of its lubricating properties.
If the fluid has metal flakes or other signs of solid particulate matter, you have likely also suffered damage to the gears and other moving parts inside the transmission.
Cooling an Overheated Transmission with Low Fluid
If your transmission overheating is caused by low transmission fluid, you can help cool it down by adding fresh fluid. The bad news is a leak likely caused the low transmission fluid, and if it’s a serious one, you might find yourself right back in this situation a few miles down the road.
How to Add New Transmission Fluid
Adding new transmission fluid to help cool down your overheating transmission is relatively straightforward. However, you must ensure your car is parked on a level surface. It also helps to have a long funnel with a narrow spout tip.
If your transmission fluid is degraded and at the HOT line, and/or you see metal flecks in the transmission, the wise thing to do is have the car towed to a transmission specialist.
If the transmission fluid looked normal or was simply low, you can take the next half hour to an hour to let the transmission cool down while you investigate what caused the overheating problem.
What Causes Transmission Overheating?
Transmission overheating can be caused by driving conditions, severely hot weather, low transmission fluid, bad transmission fluid, or mechanical failures in the transmission. Ferreting out what caused your transmission to overheat will factor into whether or not you should still drive it again, even after it cooled down.
1. Long, Heavy Towing Sessions
Towing adds excess energy and heat from friction inside the transmission, which can overheat a transmission to the point where you need to stop to let it cool down. In a heavy towing session, the engine is probably also running hot, which makes it harder for the radiator to dissipate heat.
In a perfect world, you should never tow over 80% of your vehicle’s maximum towing capacity. If you see your engine temperature gauge climb on the dash display, you can bet the same thing is happening to the transmission.
If you’re over the 80% mark, or you’ve been towing for a long time, but the transmission fluid still looks good on the dipstick, you might get away with letting it cool down. Then you can drive again for a short distance. At some point, you’ll have to reduce the load or be stuck in this cycle of heating and cooling a transmission until something finally breaks.
2. Heavy Stop-and-Go Traffic
If you get caught in heavy stop-and-go traffic, and the weather is hot, it can increase the transmission temperature and engine, causing both to run hot. If your transmission fluid is old or slightly degraded, it can increase the transmission’s friction and increase the risk of overheating.
If, after you let the overheated transmission cool down, you find the fluid looks dark, you might want to consider getting the car towed. Though if it’s just a little brown, you might be able to make it a short distance without the risk of severe transmission damage due to degraded transmission fluid.
If the fluid looks translucent pink still, you might be able to let the transmission cool down. Then perhaps find an alternative route with smooth traffic flow. Then when you get a chance, the wise move is to have a mechanic perform a complete transmission flush and fill.
3. A Leak That Causes Low Transmission Fluid
Even if you cool down your overheated transmission by adding new fluid, chances are good that a serious leak caused the low fluid levels. Transmission fluid is an oil and essential for lubricating all the moving parts inside the transmission. If you drive with an undiagnosed fluid leak, your transmission will inevitably overheat again, and you might not be able to cool it down in time to prevent serious damage.
If you’re lucky, it’s a minor leak in an axle seal or a slightly deformed oil pan gasket, which will let you drive a short distance home once it’s refilled.
If it’s a major leak around the output shaft, a hole in the oil pan, or a blown transmission line leading to the radiator, you’ll quickly lose transmission fluid again once it’s refilled. In a moment like this, the wise move is to have the car towed.
4. Bad Transmission Fluid
If your transmission overheated before and went unnoticed, the degraded fluid will have lost some or most of its lubricating properties. However, transmission fluid has a lifespan of roughly 30,000 to 50,000 miles before it starts to break down, regardless of overheating.
Getting the car towed is best if your transmission fluid looks dark, brown, or sticky. Even if you top the transmission up with fresh fluid, it will still not have the full lubricating properties you need to drive it without risking unnecessary transmission damage.
5. Contaminated Transmission Fluid
If you manage to cool your transmission down but check the fluid to find particulate matter or metal flecks in the fluid, then you should still consider the car undrivable. In a case like this, something has broken down in the transmission, gear, and grinding, or something has degraded. It’s causing excess friction or preventing important components like solenoids from operating correctly. The car needs to be towed to a transmission specialist.
6. A Problem with the Radiator
If the engine radiator has a problem, gets clogged, or the blower fan fails, it can impede the transmission’s ability to dissipate heat as you drive. This type of fault causes gradual overheating, and you’ll also notice the engine’s temperature gauge is running hot.
In a normally working radiator, the coolant passes through the core and cools, settling into the bottom, where it passes over a metal tube that holds recirculating transmission fluid. This tube within a tube allows the cool engine coolant to pass over the transmission fluid, extracting heat energy.
In a case like this, you might be able to let the engine and transmission cool down after an hour or so. Then you can drive a short distance before you’ll see the engine temperature gauge rising. Then you must pull over to cool the transmission down and keep the engine from overheating.
7. A Problem with a Transmission Solenoid
Your transmission relies on solenoids to help move transmission fluid for shifting gears and shunting fluid to the radiator to dissipate heat. If a solenoid gets stuck, the engine can rev too high, heating up the cooling system. It can also make it difficult for fluid to circulate efficiently between the transmission and the radiator, causing it to overheat.
Sometimes a stuck solenoid will cause the transmission temperature to slowly creep up until it reaches a point where the overheating in the transmission fluid and moving parts causes erratic gear changes. It might drop into neutral or get stuck in neutral, leaving you stranded and hoping you can cool down your transmission fast.
How to Maintain Transmission Temperature
Maintaining a safe operating transmission temperature starts with good maintenance habits and thoughtful driving. Being aware of your engine and transmission temperature will also reduce the risk of you ending up on the shoulder trying to cool your transmission down as fast as possible.
1. Good Maintenance Practices
Good transmission maintenance practices are the first step in keeping a properly cool transmission. This means changing the fluid every 30,000 to 50,000 or as the manufacturer recommends. It also means caring for the engine cooling system to ensure the transmission lines can efficiently dissipate heat.
2. Check Your Transmission Fluid
Maintaining a cool, properly functioning transmission also means monitoring your transmission fluid. Check the level and look for signs of degradation, metal flakes, or discoloration on the dipstick. Catching fluid problems early will keep you off the hard shoulder.
If your transmission fluid is low, you must do your due diligence checking for leaks and having them repaired.
3. Upgrade to a Larger Oil Pan
A larger transmission oil pan increases the total fluid volume passing through the transmission and the radiator. This gives you a larger overall heat sink to dissipate transmission heat. If your transmission does get hot, a large transmission oil pan will also help it cool down faster!
4. Have a Transmission Radiator Installed
There are aftermarket transmission radiators that you can have installed for around $250 to $350. They are designed to cool the transmission without interference from engine heat specifically. Some heavy-duty pickup trucks are starting to come with them standard, and many people experienced with towing heavy loads will tell you they’re a “Must-Have” accessory.
How Does a Transmission Cooler Work?
If your transmission overheated due to the routine stop-and-go traffic on your daily commute or because you were towing something reasonably heavy, the smart move might be installing a transmission cooler. Also known as a transmission radiator, it’s an additional reservoir with cooling fins, making it much easier for the transmission to dissipate heat.
It will increase the volume of transmission fluid in the system, which you’ll need to account for when you install and top up your radiator fluid. Though this also increases the heat sink potential of the transmission.
Many contractors and construction workers who do a lot of towing will have an aftermarket transmission radiator installed as insurance against overheating.
Once installed, it slightly modifies the transmission cooling process. Hot transmission fluid is diverted from the transmission to the radiator like normal, releasing a modest amount of heat energy.
The transmission fluid then travels back through the return line, passing through the cooler, which is larger than the tube moving through the engine radiator. The still-warm fluid then moves over the fins of the transmission cooler to further lower the fluid’s temperature. Then the much cooler transmission fluid is returned to the transmission to complete the loop.
This extra step in the process and the significant cooling potential of the transmission radiator. It’s the perfect way to keep your transmission cool when you’re towing heavily or frequently dealing with bad traffic conditions.
Choosing the Right Transmission Cooler
There are three different types of transmission coolers to consider. They are tube and fin, plate and fin, and stacked plate. The best automatic transmission coolers are typically made out of aluminum, which does a very efficient job of dissipating heat.
i. Tube & Fin Transmission Coolers
With these transmission coolers, a tube weaves throughout the radiator, maximizing the surface area interaction with the air. At the same time, the fins on the outside absorb some of the heat energy, which naturally dissipates into the surrounding air in the engine bay. However, tube and fin coolers are often the least efficient type of cooler.
II. Plate & Fin Transmission Coolers
These transmission coolers use a series of horizontal parallel plates that give it a look similar to a miniature engine radiator. Hot transmission fluid moves through each row of smaller plates which helps to cool the fluid faster and more effectively. They tend to be more efficient than the tube and fin transmission radiators as the increased surface area allows more fluid to contact the cooling surface.
III. Stacked Plate Transmission Coolers
Stacked plate transmission coolers are the most popular and efficient type of transmission radiator. They look a little like plate and fin coolers. However, they have larger internal tubules that offer superior airflow and heat dissipation. Stacked plate transmission coolers force fluid through the cooling plates to lower fluid temperature faster and more efficiently.
Stacked plates are also the easiest transmission radiator to install and remove. If you’re looking to save a lot of money by handling a DIY transmission cooler install, then a stacked plate cooler is what you want to go with.
What To Look For In a Stacked Plate Transmission Cooler
When looking for the best-stacked plate transmission cooler, you must prioritize one made from aluminum. You also want to prioritize the highest possible GVWR comparable to your vehicle.
This is proportional to the transmission’s load when the vehicle is fully loaded. You can usually find the GVWR statistics for your make and model in the driver’s side door well.
To help save you time, we’ve found some of the best online options. The price for the following transmission radiators is the same or less than what you’ll pay at most auto parts stores.
Best Transmission Cooler for Trucks & Full-Size SUVs
Our Product Choice: Acmango 19 Row AN10-10AN Stacked Plate Oil Cooler
Best Transmission Cooler for Sedans & Mid-Size SUVs
Our Product Choice: EVIL ENERGY 15 Transmission Engine Cooler
Best Transmission Cooler for Small Cars
Our Product Choice: EVIL ENERGY KT01075BK Transmission Engine Cooler
How to Install a Transmission Cooler
Installing your own transmission cooler will save you around $150 to $250 in mechanic labor costs. However, this is the sort of DIY job that’s best reserved for accomplished DIY mechanics. Time-wise, you can expect installing a stacked plate transmission cooler to eat up a Saturday afternoon completely.
When you have the correct transmission cooler for your size vehicle, you can install it using the following steps.
This can vary by make and model; you might need to get creative. Most of the time, it’s best to mount it just in front of the AC condenser grid. Just be sure not to touch or puncture the condenser accidentally.
Keep a rag close by to catch any drips of transmission fluid.
You might need to use a utility knife to cut the hose down. Ideally, you want it to marry back to the transmission cooler with less than half an inch of slack.
Frequently Asked Questions
Can I Take a Car with an Overheating Transmission to a General Mechanic?
If your car’s transmission overheated due to a serious mechanical fault within the transmission, and you see signs like metal flakes in the fluid and grinding gears, it’s best to have it towed to a transmission specialist. They have more experience working with transmission problems and special tools for transmissions. This will also translate to slightly lower labor costs, which is usually the biggest part of a transmission repair job.
If your transmission overheated due to a situational issue, such as towing too heavy or abusive driving practices, and the fluid looks a little degraded, then you can have it towed to a general mechanic. In most of these situations, the fluid and filter must be replaced, and hopefully, the transmission will run like normal again.
Does Idling Cool Down a Transmission?
When an engine is idling, it does a very poor job of cooling via the radiator. The transmission fluid also moves very slowly through the system, which makes it increasingly hard for the radiator to have any appreciable cooling effect, especially if the radiator fan isn’t working well, even though you’re not getting any additional heat from the friction of the transmission gears moving.
Ultimately, if you want to cool your transmission down fast, you need the engine to be off. Ideally, you could park the car nose into the wind with the hood open.
How Long Does It Take Transmission To Cool Down?
If you catch it early, a small transmission as you’d find in a hatchback or a small sedan, could cool down in around half an hour. A large pickup truck that was badly overheating while towing a heavy load might take as much as 60 to 90 minutes to completely cool a hot transmission.
How Do I Check My Transmission Temperature?
The easiest way to check the temperature of your transmission is to point an infrared thermometer at it. When you pull the trigger, the little red dot will give you the surface temperature. You’ll get the most accurate temperature reading by taking at least 2 to 3 samples from the transmission oil pan under the car.
If these readings are over 240 degrees, your transmission gets too hot. The threshold for severe transmission fluid breakdown and transmission damage starts at around 260 to 270 degrees. If you’re getting a temperature reading that high, chances are good that even once the transmission has cooled down, the fluid will have lost much of its lubricating properties.
Conclusion
If your transmission is overheating, you need to get cool it down as fast as possible. This starts with pulling over, setting the parking brake, and popping the hood. Take a quick look around for leaks and check the transmission fluid.
If the fluid is low, you can help cool the transmission down by topping it up. Though you likely have a transmission fluid leak somewhere that you need to deal with in the mix, or you will end up right back at square one again.
If the fluid is dark or has metal flakes or other contaminants in it, the wise move is to have the vehicle towed to a transmission specialist.
If the transmission overheated from stop-and-go driving or you’ve been towing near the 80% threshold of the maximum towing capacity, you’ll have to let it cool down. From there, you’ll need to lighten the load or choose an alternative route with more smooth-flowing traffic.
Written By
Jason Farrell
Jason Farrell is a certified master technician, the editor of Mechanic’s Diary in Pittsburgh, Pennsylvania. He is ASE (Automotive Service Excellence) certified and earned a Bachelor’s Degree in Automotive Technology from Pittsburg State University. With nearly 18 prior years of experience in the automotive field, he has extensive knowledge about Domestic, European, and other foreign makes and models of cars and light trucks. Jason’s experience working as a technician and service manager at dealerships, gave him the experience and know-how of most aspects of inspection, diagnosis, and repair from engine and drivability to electrical, HVAC, brakes, steering and suspension and everything in between.