Your Mazda Miata relies on a thermostat to control the temperature of the engine. When it goes bad, you’ll experience a number of different problems. Some of the most common symptoms of a bad thermostat are no heat, a spiked temp gauge, blown head gasket, and more.
Symptoms of a Bad Thermostat: Mazda Miata
There are a few ways that your Miata will tell you that your thermostat is bad. Hopefully you’ve caught them before any damage was done. Thermostats are very inexpensive, f you do end up needing one. Here are the most common signs of a bad thermostat.
The most common symptom of a bad thermostat is overheating. The thermostat doesn’t open up. This keeps the coolant from entering the engine. When this happens, the coolant in the radiator stays relatively cool, and the engine overheats fast.
Blown Head Gasket
If your Miata runs too long without coolant circulating through the engine, the head gasket can blow. Signs of a bad head gasket include:
- rough idle
- bad fuel mileage
- water in the oil
- a lot of white smoke from the exhaust
A head gasket is a very costly and time consuming repair. Hopefully you’ve caught your bad thermostat before this has happened.
If your Miata has no heat at all, it is entirely possible that the thermostat is stuck open. When this happens, coolant constantly cycles through the engine. On very cold days, this cooling capacity is not needed, and the engine never warms up. Here’s more on no heat diagnosis if this is what you are experiencing.
Warning Light or Temp Gauge Spiked
The first sign of a bad head gasket that most people are going to notice is a warning light or spiked temperature gauge. If you’ve noticed this, you need to get off of the road and get your Miata’s engine shut down as soon as possible, before any lasting damage can occur.
A bad thermostat can cause the temp gauge or warning lights to come on. But, it’s not the only reason. Other things that can cause the temp gauge to spike are:
- Low Coolant- If your Miata has been losing coolant, it’s possible that you’ve finally leaked out enough that the cooling system can no longer do its job.
- Bad Radiator- If the radiator has been clogged enough that coolant can no longer pass through efficiently, your Miata will overheat.
- Water Pump- The water pump is responsible for pushing coolant through the radiator and the engine. When it goes bad, water can’t circulate through the cooling system, even if the thermostat is open.
Coolant Leak Around the Thermostat
As pressure builds around a bad thermostat that is stuck shut, you’ll notice that there may be coolant leaking around the thermostat housing. This leak is not the cause, but rather a symptom of your Miata’s bad thermostat.
Conclusion: Miata Bad Thermostat Symptoms
Replacing a thermostat is a relatively affordable repair. If you have reason to believe it’s gone bad, ignoring it will only end up costing a lot more money in the long run.
Good luck diagnosing your Mazda Miata. If there is anything that you would like to add, please leave a comment below.