Mercedes W201 Overheating? How to Replace your 190E Thermostat

Is your Mercedes W201 overheating? This is a common issue and we are here to show you one of the easiest solutions that would possibly save you from having to replace something costly like the head gasket. You wouldn’t want to go through that trouble without knowing for sure if that is the issue. If your 190E thermostat is bad, it’s a potential quick and cheap fix to get your car running at the proper temperature again.

What is Causing My 190E to Overheat?

Overheating is a symptom of head gasket wear, but it doesn’t always have to be. If your car is reaching temperatures well above 100°C, or even maxing out the gauge, you should stop driving it until you diagnose the issue. Operating your car at those temperatures for extended periods of time can cause costly damage to your engine. I was able to fix my overheating issue on my 1992 190E 2.3 by making one simple repair: changing the thermostat.

There are many different reasons that could cause overheating from a simple thermostat to a costly head gasket. If you are not losing coolant (which means there isn’t a coolant leak) checking up on your 190E thermostat is a cheap and great first step to diagnosing the issue.

To hear about my experience with overheating on my W201, continue reading. If not, feel free to skip to the bottom to read about how to change the thermostat on a Mercedes W201, and where to buy one. The thermostat I recommend below fits many classic Mercedes models, and it also offers a nice 2-year or 40,000 mile warranty!

My Experience with an Overheating 190E 2.3

I’ve always noticed that my 190E 2.3 tends to run a bit hot, especially because I only drive it in the summer heat. It also doesn’t help that most of my miles are in heavy city traffic, which contributes further to the overheating. I had just replaced the battery on my car, when of course, another issue arose.

For a week, I noticed my temperature gauge on the highway would read about 90°C (slightly higher than the usual 85°C). In traffic, it would slowly creep up to about 100°C, at which point the auxiliary fan would kick on. I knew something was wrong when that auxiliary fan would never turn off again. The fan was not providing enough cooling to bring the engine down in temperature.

The auxiliary fan kicks on somewhere around 100°C, and then it cools the engine enough to where it would turn off again. Since the fan itself was working fine, I decided to look elsewhere for an issue with my cooling system. The first spot I looked was where the issue was, the thermostat.

What Does a Car’s Thermostat Do?

The thermostat on a car serves a crucial role in both allowing the engine to heat up, and also cooling it down. Thermostats have a temperature rating on it, my 190E thermostat was 88°C. The thermostat opens up at that temperature and sends coolant to the radiator for cooling. As your car’s thermostat gets old, it may get stuck and unable to open. This will prevent coolant from reaching the radiator, causing your engine to overheat.

If you are experiencing similar symptoms, I would first recommend you to stop operating the vehicle, as driving at heightened temperatures can cause engine damage. Secondly, I would recommend you check your car’s thermostat with the tutorial below, or bring it to a trusted mechanic.

How To Change Your 190E Thermostat

1. Before attempting this tutorial, allow your car to cool off completely. When hot, your coolant system is under pressure and will spray hot coolant if opened. Coolant is very toxic, use gloves and have a cloth handy, as some coolant may spill during the process.
2. Gather your items for the process. You will at least need a 10mm socket, a new thermostat, a new thermostat gasket, and gloves to protect your hands. I reccommend you also have a cloth and pliers if necessary.
   
3. The thermostat is located at the top of the water pump beneath the thermostat housing. The thermostat housing has two hoses attached to it, and it is secured on with three 10mm bolts.
   
4. With a 10mm socket, remove the three bolts that hold down this thermostat housing. Be cautious not to drop the bolts or washers into the engine bay.
5. For the next step, use a cloth in case any coolant spills out. Once the bolts are removed, carefully remove the thermostat housing without pulling on the hoses attached to it. Be ready to catch any spilled coolant with a cloth, as you don’t want it spilling all over your engine bay.
   
6. Once the three bolts are removed, you can now check the condition of your thermostat. In the photograph, you can see that my old 190E thermostat was quite corroded. It needed to be replaced, and was the culprit to my overheating problem. I used a set of pliers to grab the top of the thermostat and remove it, as it was a bit difficult to pull out. The picture below shows the condition of the bad thermostat off the car.
   
7. Installing the new thermostat is as simple as placing the new one in the same spot as the old one. Ensure you installed a new seal around it as well. 
8. Replace the thermostat housing on top of the new thermostat, and secure the three bolts back in place.
9. If any coolant spilled out while working on this project, ensure you replace it. Whenever working on the cooling system, it’s possible to introduce air into the system. In that case, you would have to bleed the air out of the system afterwards as well.

Let us know in the comments below if this fixed your overheating issue. Read more about the technical specs of the Mercedes 190E here!