Has Your Car Caught A Winter Cold….. It’s Probably Got A Faulty Thermostat?

Diagnosing a Faulty Thermostat

At Alfa Men, we can’t tell you how often we examine a first-time customer’s car and find that the thermostat is faulty. It’s just one of those parts that everyone forgets about. We understand why…. when it fails, it makes no noise, there’s no vibration… in fact the issue is so subtle that some drivers go years without ever noticing it.

Why write a post about it you may ask? Well, the thermostat is a vital components of your car’s engine. With a faulty thermostat, engine life is reduced by approximately half, fuel consumption increases by about 5-10% and your engine is certainly not performing at it’s peak. In fact, most engines will be down on power by a significant amount. Additionally, your cabin heater is not able to pump out the same amount of heat that it should.

To understand why a functioning thermostat is so important, I should first explain what it does. Put simply, the thermostat regulates the amount of cold water (flowing from the radiator) that circulates through your engine so as to regulate the temperature of the engine to approximately 90 degrees celsius. This temperature is critical if the engine is going to burn fuel efficiently and release horsepower from the combustion process.

If the engine is too cold, the car’s own computer adds additional fuel in an attempt to ‘get the fire going’ (a process that never ends with a faulty thermostat). That extra fuel is often burnt poorly and large amounts of carbon (soot) are formed in the combustion chamber. That carbon makes it’s way into your engine oil and gums up the engine (both inside the cylinders and in the crankcase) with carbon deposits. It’s mainly the carbon deposits that lead to excessive wear, black engine oil and other issues. Other outcomes from a failed thermostat include aspects such as temperature cycling which also contribute to expensive head gasket failure…. that’s a whole larger can of worms that we’ll discuss another time.

So how will you know when your thermostat is faulty? There are some simple tests that owner’s can perform to determine if their thermostat is functioning correctly. Firstly, take notice of how long your engine takes to warm up (to half way or 90 degrees on the gauge) in cool weather… is it a 5 minute process on a winter’s morning or is it closer to 10-15 minutes? It should be close to 4-5 minutes and if it’s not… suspect a faulty thermostat.

Another test which is a little harder to judge because it’s more dependant on traffic is: When your next driving down a freeway (or any continuous road) for a distance of 3-5 kms at high speed (anything above 70km/h) have a look at what your temperature gauge reads. If your engine is sitting at anything below 85 degrees, your thermostat is almost certainly faulty!

How do I test customer’s thermostats? Well that’s a trade secret…. kidding. With the engine idling in the garage (and already warmed up), I activate the car’s radiator fan using Alfa diagnosic software. After 5 minutes with the fan on, I use the diagnostic software (and potentially a infra red thermometer if I think the temp sender is faulty) to test the coolant temperature. Anything below 85 degrees is a fail.

So why do thermostats fail so often? Thermostats generally only last 6-8 years. Sure, some last 10 years but they are the exception not the rule. Some even fail as early as 2 years. This means, that if you own a car that a 2007 model or earlier and you haven’t had a new thermostat installed, chances are, your car’s thermostat is faulty.

Is it expensive to repair? Not at all. Most thermostats range in price between $30 and $150. Some come as just inserts, other come as larger assemblies with alloy casings. To install a new thermostat, most mechanics will charge for one hour of labour plus a little coolant.

At the end of the day, replacing the thermostat might be one of the best repairs you’ll ever get done. Firstly, you’ll be saving fuel and saving the planet (i can’t believe I just said that). You’ll be extending the life of your engine significantly and unleashing more horsepower in the process. As far as repairs go, it’s the ultimate win win. A cheap repair that unleashes extra horse power and economy… who can complain!

If you have any questions about your own car or any of the information given in this post, please give us a call.

Regards, Matthew Long

Workshop Manager at Alfa Men.

Written by

As a keen car enthusiast and with a strong background in automotive workshop management, I always wanted to establish an Alfa Romeo specialist workshop in Melbourne's west. Alfa Men is the product of that desire and I cannot thank our loyal customers enough for their support and input to our family owned business.

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