Car Transmissions

Transmission Overheating Symptoms And Causes

Mike Cross
Updated Oct 31, 2021
Transmission Overheating Symptoms And Causes

One common problem with aging cars is the transmission overheating. There are a few different things that can cause this. Some are simple to fix, while others will cost you an arm and a leg. If the transmission is overheating, you need to act right away. Running just twenty degrees too hot can cut the lifespan of your transmission in half.

There are many plastic and rubber parts in the transmission that can't stand high levels of heat. If you run the car too long with the transmission too hot, these parts will fail. Your vehicle will leak more transmission fluid, causing metal parts to slip. When the metal parts slip and grind, they stop working right. If you drive very long with an overheated transmission, you are begging for an expensive repair.

Fortunately, it’s easy to tell if your transmission is running too hot. There are also some easy fixes that you might be able to employ, too. Knowing that you have a problem and treating it quickly is the best way to head off a complete transmission rebuild.

How to tell if your transmission is overheating

There are several signs that your transmission is overheating. The most obvious sign is that the transmission warning light comes on. This light looks like a gear with an exclamation point in the center. Other signs that you might notice while driving are:

  • A burning or smoky smell while you are driving.
  • Shifting gears takes a long time.
  • The transmission slips or has a hard time shifting gears.
  • You hear a grinding noise when the vehicle shifts.

Other than the warning light, the other clear sign that the transmission is overheating is the color of your transmission fluid. You need to get under the car to check the fluid. Fresh transmission fluid is bright pink or red. As the fluid ages (or scorches), it turns dark red, brown, and eventually black. Old transmission fluid doesn’t cool or lubricate as well as fresh fluid.

If the transmission fluid is brown or black, you need to change it. Drain the old fluid and dispose of it properly, then add new fluid. You may find it easier to take the car to a mechanic for this; they have equipment in place to handle the old fluid.

Transmission Overheating Symptoms And Causes
Transmission Overheating Symptoms And Causes

Causes of overheating transmission

Several things can cause your transmission to overheat. Some can be fixed quickly, while others will require an expensive trip to a mechanic. The causes of a hot transmission are listed here from easiest to hardest to fix:

Operating conditions

Extreme operating conditions can cause the transmission to overheat. Towing a heavy trailer is the top operating cause of overheating. Climbing long, steep hills can also get the transmission hot. Extreme stop-and-go driving or high outside temperatures can also cause problems. Things get even worse if you combine two or more of those conditions. The best way to stop these conditions is to avoid them if you can.

Be aware of conditions that can cause transmission overheating. If you pull a trailer, know the rated capacity of your vehicle and don’t exceed it. If you frequently encounter harsh conditions, you may want to consider adding an auxiliary transmission cooler to your car.

Low transmission fluid levels

Transmission fluid serves to reduce friction in the transmission and carry away heat. If the fluid level is low, the transmission will get hot. Check your transmission fluid level by getting under the car and finding the transmission dipstick. You may need to check the manual to locate the dipstick and learn how to read it.

If the fluid level is low, you should also check for leaks. Transmission leaks will show up as oily stains around seams or bolt holes. Tighten the bolts around the leak to guarantee that everything is tight. Adding Stop Leak to the transmission fluid can seal up small leaks, while significant leaks will require a trip to a mechanic for new gaskets.

Cooler problems

If the transmission fluid is full, check the radiator to make sure it’s clean. A radiator that is clogged with leaves, dirt, or other debris won’t cool the fluid. Cleaning the junk out of the radiator will make a world of difference. Use an air compressor or a garden hose to flush the mess out of the radiator.

Check the filter for the transmission fluid, too. A clogged filter will prevent the fluid from circulating correctly. If the fluid can't flow, it can't cool. You can also check the lines circulating fluid between the transmission and the radiator. Clogged lines also stop circulation and cooling.

Faulty temperature sensor

Faulty temperature sensor
Faulty temperature sensor can make transmission overheating

If the fluid level is adequate, and the fluid is circulating, the problem could be the temperature sensor. A defective sensor can lead to the warning light coming on when it shouldn't, or it could keep the fluid from circulating when it should. The temperature sensor is a relatively easy fix, but you may need a trip to a mechanic to check it.

Serious transmission problems

If none of the items listed here are a problem and the transmission is still overheating, that is a bad sign. It means that something inside the gearbox is rubbing and generating friction. If there is a mechanical problem in the transmission, you need to see a mechanic. This will almost certainly be an expensive repair, so get your pocketbook ready.

Wrapping Up

The transmission is a vital part of your vehicle. It is the part that brings power from the engine to the wheels. It also keeps the motor working at its most efficient level while you drive. If your car experiences trouble shifting, makes grinding noises, smells smoky, or has a warning light – you may have an overheating transmission problem.

If you think there is a problem, make sure you are operating the car within normal parameters. Check your transmission fluid and verify that the cooling system is working correctly. An overheated transmission isn't a big problem by itself but left untreated, it will lead to massive headaches later on.

Mike Cross
Life is too short to drive with stock audio

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