If you’ve got a Toyota that’s running hot, odds are the problem is related to one of the following issues.
Coolant Level is Wrong
If your coolant level is too low, your engine is going to warm up hotter than it should. This is because there’s not enough coolant to make your coolant system 100% functional. So, step one when you see a hot temp gauge is to check the coolant level of your vehicle. If it’s low, add coolant (but be sure you’re adding coolant the right way, so check your manual).
NOTE: Do *not* open the radiator cap on a hot or warm engine. That’s a great way to burn yourself. Just check the coolant level in your vehicle’s overflow tank, or – if your vehicle is sufficiently aged – wait for the engine to cool off and check the radiator by removing the cap.
Cooling Fan Problems
Your Toyota is almost certainly equipped with an electric cooling fan, which helps to draw in cool air through the radiator in situations where your vehicle isn’t traveling fast enough to cool off otherwise (like when you’re stuck in traffic and not moving). If you’re having a heating issue and happen to notice that the temperature heading up while sitting in traffic, you may want to check the function of the electric fan. You should hear the fan kick on at some point. If it doesn’t, odds are:
The fan motor is bad – You may have a bad fan motor. You can test this when you are at home by finding the radiator fan switch and disconnecting the wiring harness. Use a jumper wire and insert it into the two contacts. If your fan does not come on, the motor is bad. Another way to check the fan is to turn on the air conditioning in the car. The cooling fan is usually activated when the air is running at medium or high speed.
The fan switch is bad – The fan switch comes on when the coolant is a set temperature. You can test the switch by disconnecting the wiring harness and using a jumper wire on the contacts. If the fan starts, the switch is bad and needs to be replaced.
Replacing The Thermostat
A symptom of a bad thermostat is an engine that overheats at highway speeds. It may never overheat at lower speeds because it is not working as hard as it does at higher speeds. A closed thermostat will not allow enough coolant to reach the engine to cool it. If you’re only overheating on the highway, you might just replace the thermostat (especially if you’re driving an older vehicle).
Clogged or Damaged Radiator
Over time, radiators can become clogged or damaged. This is due to contaminated coolant (which can cause a clogged radiator) or a lot of debris that’s damaged the cooling fins on your radiator. Either way, if you’ve got a lot of miles on your car, a clogged or damaged radiator is a possibility.
To improve the performance of your radiator, you can try flushing the cooling system. This can often dislodge any “gunk” inside the radiator and restore a lot of the radiator’s original cooling ability. If a flush doesn’t work, and/or you see a lot of damaged to the cooling fins on your radiator, you’ll want to replace the radiator.
When it’s time to buy a new radiator, it’s important to understand that there’s a often big difference in quality between OEM radiators and discount brands (or even name brands and OEM parts). This is because OEM radiators are designed to function at higher than expected pressures, and because they’re expected to provide sufficient cooling performance even in extremely high temperatures. Toyota, for example, tests all their new vehicles in Death Valley to verify that the cooling systems will function even when it’s 120+ degrees outside.
If you replace an OEM radiator with a cheap after-market radiator, you might not notice much of a difference at first. But the first time you sit in traffic for 20 minutes, or take a road trip on a hot day, you may find that your cheap after-market radiator isn’t up to the challenge of daily use.
Contaminated Coolant and Head Gasket Problems
Last but not least, an overheating vehicle can have contaminated coolant or even a head gasket leak. Contaminated coolant is often associated with head gasket problems, but it can also be caused by a rusting or damaged cooling system component or the use of incorrect coolant.
The tell-tale signs of a head gasket problem are:
Dark coolant that contains engine oil
White smoke coming from your vehicle’s exhaust, even on a warm day
Unusual readings on your temperature gauge
If you suspect a head gasket leak, be sure to get your vehicle checked out right away. If you suspect contaminated coolant, you can try to replace the coolant and see what happens.