Internal combustion engines are like bowls of porridge from Goldilocks and The Three Bears – they work best when they’re not too hot but not too cold. So what happens if you have an engine running cold all the time? Is that harmful to the engine? What causes this problem and how to fix it? Join us as we explore the answers to all of these questions.

The Nominal Operating Temperature

Some drivers, especially those who aren’t interested in how cars work, think that the engine temperature scale has only one bad side – the hot one. After all, we’ve all seen what happens when an engine overheats, right?

Here’s the thing, though – just like an engine can run too hot, it can also run too cold. As it turns out, every engine has its optimal working temperature that revolves around 200F, give or take. Every engine is different in this regard. Some work at temps closer to 100C, others work at much colder temps.

Why is that 100 Celsius figure so important? Because that’s the boiling point for water, which just so happens to make up a decent amount of your coolant. Don’t worry, though. Most engines can reach temps higher than 100C and survive. However, it’s not something you want to experience regularly.

How Does the Engine Achieve and Maintain Optimal Operating Temperature?

We’ve already mentioned that every engine has its optimal operating temperature range, and for a good reason. The materials used and the tolerances within the engine are all calculated for a unit that runs at a specific temperature. If the block is colder than it should be, those tolerances are affected.

The key is to keep the engine in that narrow temperature band. So how do we do that? By utilizing a temperature operated valve known as the thermostat. A thermostat is an essential part of any engine cooling system.

The system itself runs coolant, often antifreeze mixed with distilled water, through the engine block using a water pump. The coolant is there to soak up the heat from the cylinders and release it at the other end of this closed-loop, within the radiator.

However, if the coolant was constantly circulating within the engine, it would never reach its operating temperature. That’s why we use thermostats.

What is a Thermostat?

As we’ve mentioned before, a thermostat is a type of valve that is activated by heat. Once the coolant reaches a specific temperature, the valve opens, and the fluid is allowed to circulate through the entire system. Until that point, the thermostat is shut off, thus preventing the engine’s coolant from leaving.

Needless to say, it’s terrible when a thermostat fails. Fortunately for everyone, a bad thermostat often gets stuck in the open position. We can thank a built-in safety feature for this little luxury. Otherwise, every thermostat failure would essentially cause engine overheating, blown head gaskets, and warped heads.

What are the Symptoms of a Bad Thermostat?

A thermostat is a very simple device, so it’s not that hard to recognize the symptoms when it decides to go bad. There are a few things that can happen:

• Car Overheating – The worst symptom caused by a bad thermostat is the engine running too hot. If this happens to you, crank the heating on your AC to the max and pull over as soon as you can.
• Temp Needle Moving Erratically – Another common symptom of a bad thermostat is the temperature gauge showing all kinds of different readings. This is caused by the thermostat remaining stuck in the open position. When the car is stopped and idling, the engine will warm up since no cold air hits the radiator. However, as you start moving, the engine will begin to cool down.

That’s about it as far as thermostat symptoms go. It’s important to address the issue no matter which one of these two symptoms you notice. As tempting as it is to drive with the thermostat stuck in the open position, it’s not advisable by any means.

How to Test a Thermostat?

The absolute best way to test a thermostat is to remove it. Since it’s a temperature operated valve, you can test it by throwing it into a pot of boiling water. If it opens when the temperature reaches around 200F, it’s good. On the other hand, if it remains closed or if it’s closed, to begin with, you’ll need to get a new one.

As far as testing it without removing the thermostat from the vehicle, you don’t have too many options. If the car is overheating, you rule out the thermostat by touching the lower radiator hose. If it’s cold and the upper hose is hot, there’s a solid chance that your thermostat is stuck closed. At that point, you shouldn’t drive the car as you’re risking overheating it.

How Long Can an Engine Run Cold?

This is a difficult question to answer. Most car people in the know will tell you that it’s just not healthy for an engine to work for any significant amount of time outside its optimal temp range. That being said, you’re not going to have an exploded engine just because you’ve decided to drive it cold to the shop.

It’s when you completely ignore the problem and continue to operate the vehicle for weeks or months that the issue can turn into a severe problem.

Here’s where the main issue lies. Sure, a cold engine wears out quicker. That’s a given. However, modern cars have a cooling system linked to the ECU. When the engine is cold, the ECU is feeding it a richer mixture to get it up to temperature faster.

If you run your engine cold all the time, you’ll most likely experience increased fuel consumption across the board. Additionally, you’ll find higher amounts of carbon buildup at various parts of the engine.

The most damaging effect of feeding a fuel-rich mixture to the engine is excess fuel reaching the exhaust. More specifically, the problem is when unburned fuel reaches the catalytic converter, causing serious damage to this component.

How Difficult is Thermostat Replacement?

Swapping out the thermostat on your car doesn’t necessarily have to be difficult, but it depends on the car itself. It’s a breeze on older cars where thermostats are standalone units bolted to the engine.

In this case, all you need to do is unhook the hoses that run to the engine and remove the broken part. However, it’s not always that easy.

In modern European cars, thermostats are built into water pumps or hoses. That can complicate things for a DIY enthusiast, but it doesn’t make the whole process impossible.

Where to Find Quality Replacement Thermostats?

If you’re looking for quality thermostats for your European car, you’re in the right place! Here eEuroparts.com, we offer one of the largest catalogs of genuine, OEM, and aftermarket parts for European vehicles.

To find a thermostat that fits your car, simply head over to our store, input your car’s year, make, and model, and our system will show you what components are available.
In case you have any questions, feel free to get in touch with our customer support service via email or by phone. Our reps are standing by to help you out.