Mazda RX-8 Overheating

Your Mazda was designed to run at a set temperature in order to deliver the best performance for its engine. Any temperature outside of the recommended range can result in damage to the engine and its components. That is why if you find your Mazda engine running too hot, you need to locate and repair the problem. 

Here's the rundown on overheating in a Mazda Rx-8 (something we wish would come back), and what you can do about it.

Causes Of Overheating

Anytime a part of the cooling system can no longer transport, absorb or dissipate heat, overheating of the engine may occur. Things like low coolant levels, coolant leaks, heat conductivity within the engine from clogged water jackets, faulty thermostats, bad radiator airflow, or defective cap can cause overheating. Additionally, if the fan clutch slips or is inoperative, you can get overheating. Hoses that have collapsed or water pump impeller that is loose can also cause overheating.


Heat will always flow from the higher temperature to an area that has a lower temperature, so the only way to cool hot metal is to keep cooler liquid on it. That is why the coolant is constantly circulated within the engine components, and should that circulation stop, the temperature will begin to rise.

When the coolant is heated by the engine, it has to be able to get rid of the heat before it goes around again. This happens in the radiator, and if the radiator is not working or is clogged with debris, its ability to lower the temperature of the liquid is greatly diminished. All the tubes, hoses, and internal workings can become clogged with rust or junk. Your cooling fan must be working in order to cool the liquid down.


The thermostat is responsible for maintaining the right temperature, and if it does not open, it will not allow coolant to flow to the engine. This can cause overheating.


The exhaust takes the heat away from the engine and dissipates it, so if you have a restricted catalytic converter or a crushed pipe, you put a restriction on the flow of heat. This can cause the engine to run too hot.

Temperature Gauge

It may be that the temperature gauge is faulting, and you are not really overheating. There may be a warning light on due to a bad coolant sensor due to air trapped underneath the sensor or a low level of coolant.

Consequences Of Overheating

Should your RX-8 overheat for long enough, it can cause catastrophic damage to its engine. Think damage to the pistons, rings, and rod bearings. If the overheating is too extreme, you can blow a head gasket. Since aluminum swells three times faster than the cast iron, it distorts and swells the head, and this can squeeze the gasket until it gives under pressure.

Never ignore your hot warning light. Stop driving as soon as you see it illuminated. Let the car cool down and look for the problem. Do not drive while the car is running hot or you risk destroying your engine.

Troubleshooting For A Solution

Cooling system diagram

System Leaks – This is the number one reason why a vehicle overheats. You should check hoses, caps, heater cores, the radiator, water pump, head gasket, freeze plugs, thermostat housing, automatic transmission oil cooler, block and cylinder heads for leaks.

Take a look around your cooling system, and then run a pressure test to locate internal leaks. This will show you where fluids may be seeping out around hoses or even cracks in the head. Your system should be able to handle 12 to 15 psi for at least 15 minutes without a loss of any pressure. Any pressure leaks usually point towards an internal leak like the head gasket, a cracked cylinder, or block.

Be sure to do a pressure test on the radiator cap in order to determine that the boiling point is correct.

Thermostat – You can test your thermostat to see if it is the problem by starting the engine and putting your hand on the upper hose to the radiator. It should not be hot until the engine has warmed up. If the hose is not hot at all, it is because the thermostat is not opening up. You can also test it by taking it out of the vehicle and dropping it into a pan that contains boiling water. It will open up if it is good.

Replace a faulty thermostat with one that is recommended for your Mazda RX-8. Using an incorrect thermostat can prevent the RX-8’s computer from operating properly.

Head Gasket – This is an expensive repair. A leak in the head gasket lets coolant run into the cylinder or the crankcase. You will notice white exhaust smoke when you start the cold engine. Run a pressure test on the cooling system, or use a block checker to pull air from the system and place it in a container filled with a leak detection liquid. If there are gases in the coolant, the leak detection liquid will change colors from a blue to a green color. You may temporarily seal a head gasket leak with a sealer that can be added to the radiator. Some leaks cannot be sealed, and the gasket needs to be replaced.

Fan - A bad fan clutch can cause the fan to stop working. The clutch can wear out over time, and if it leaks, freely spins, wiggles or wobbles when the fan is pushed in or out, or has no resistance, you should replace it.

Make sure that an electrical fan that it cycles on and off when the engine heats up or cools down. If it does not come on, check for wiring problems, a faulty relay switch or a bad temperature sensor. You can jump the fan with a jump wire and the battery, and should it jump-start, there may be a problem in the wiring, sensor or relay. If you cannot jump-start it, then it is bad.

Additionally, if you are missing the fan shroud, you need to replace that because it improves the cooling ability by 50 percent. A loss of that much in cooling ability can cause the engine to overheat.

Water Pump – A water pump that has a leak or has a wobbly pump shaft needs to be replaced. The pump can be the cause of an overheating vehicle due to corroded or loose impeller vanes. Additionally, if the water pump is the wrong one for your car, you may also see an overheating issue. Serpentine belts that are loose or broken can cause the water pump to stop working.

There have been occasions where the impeller comes loose and stops turning. The water pump pulley will appear to be working properly. Without the impeller spinning, there is no circulation of the coolant to the engine. The only way to check this is to take the pump off and look at the impeller for corrosion or check to see that it is secure. Corrosion reduces the clearance between the impeller and the housing, which reduces the flow of coolant.

Belt – Check the belt condition and ensure that it is tight. If the belt is slipping, it can keep the water pump from operating properly.

Lower Radiator Hose – This hose can collapse or become pinched, which will block the coolant’s flow. There is a metal reinforcement wire inside this hose to help keep its shape, and the wire may have rusted or corroded enough to allow the hose to collapse.

Radiator – The radiator can become dirty or plugged from debris, dead bugs, and dirt. This will block the airflow through it, which results in a loss of the ability to cool down. There may also be internal debris that blocks the flow. You can use an infrared thermometer to check the radiator for spots that are cold. If it is clogged up, then take it off and clean it out. You can backflush the system in order to remove any rust or scale, but you still need to remove the radiator and clean it out.

When you refill it, make sure that you refill it completely, so there is no air trapped inside. It can get trapped under the thermometer, in the head, or the heater core and retard the cooling circulation. You may need to loosen up a heater hose to get the air out if there is no bleeder valve.

Exhaust Backpressure – A catalytic converter that is clogged will slow down the exhaust flow and cause the engine to heat up. Check the pipes for damage since an exhaust pipe that is crushed can cause the engine to overheat. Take a reading of the vacuum at idle to determine if there is a restriction in the exhaust system. If the intake is low and keeps dropping, there may be a problem in the exhaust.

Overheated Air – On a vehicle that has a throttle body injection or a carburetor, look for heated air within the intake system on the air cleaner. The temperature control valve could be stuck and letting air from the exhaust manifold enter into the air cleaner without any offsetting cooler air. This can cause an overheating engine. Additionally, look at the heat riser valve to make sure that it is not stuck shut. There will be manifold heat on the older V6 and V8 engines.

Brakes – If your brakes are dragging due to a stuck caliper, your engine is trying to work harder and may be overheating because of this. Look at your brakes and your parking brake to see if there is a problem.

Overworked Engine – Any vehicle that has been overworked by trying to pull the excess weight up mountains or towing over its capacity will overheat. If you are planning on doing this type of driving normally, then replace the stock radiator in your Mazda RX-8 with a larger radiator built to deliver more cooling power to the engine.

If your Mazda is overheating, these suggestions may help you determine the cause of your overheating. Should you be unable to determine the cause of the overheating, then you may need to consult with your local Mazda dealership and get professional assistance.