2003 VW GTI 1.8 Turbo Thermostat Replacement

This 2003 Volkswagen GTI 1.8 Turbo came into the shop with a customer request of replacing the Thermostat. The CEL had illuminated and the customer had taken the vehicle by an auto parts store and had the codes checked. The code was a Tstat code and he was advised to replace the thermostat.

Below is a picture of where the thermostat "lives" on these vehicles. Basically, if you notice the alternator to the left; the thermostat "lives" to the right of the alternator (as you look at the picture). It is between the oil dip stick and the alternator. As you can see, it would be very difficult to "fish" out as is. Many manuals and data services will tell you to remove the alternator assembly to replace the thermostat. But we have found an easier, less time consuming method for doing this job.

First, of course, we drained the coolant. Next we removed the plate. There are two Allen head fasteners that need to be removed. In the picture below, I am removing the one on the left (again, with the orientation of looking down) and have already backed out the one on the right.

The picture below shows both bolts removed and now the plate can be moved out of the way. The plate must also be removed from the oil dipstick (simply by pulling up, gently on the plate) and the electrical connector needs to be detached.

Below is a picture of the disconnected wiring harness.

Once that is done, the plate can be moved over to the driver's side and positioned out of the way. It is still connected to the car, so it cannot be removed from the vehicle completely; though you could go through the trouble of doing that. But it will position out of the way just fine to do the job. (You may have to keep it held by a bungee cord or the like: be careful not to break anything though!)

Now, the thermostat neck and radiator hose can be clearly seen, with the plate moved out of the way.

Below is a closer look at the tstat housing and hose.

We then remove the hose from the tstat housing. Below is a picture of that.

Now there are two bolts that hold the tstat housing in place. We used a 3/8 rachet, an extension and a flex socket to remove these two bolts. Sorry, we did not take pictures of this, but it is pretty easy to do. You may need a magnet to remove the bottom of the two bolts (and to put it make when reassembling the housing).

In the picture below, the bolts have both been removed from the housing.

In the picture below, the tstat is visible as the housing has been removed. 

Below is a picture of the tstat.

Below is a picture of the tstat housing/neck.

 To reassemble, we simply reversed the steps. We refilled the vehicle with coolant. We then cleared the codes and made sure the new thermostat worked properly; that the temperature hand read normally; and that the cooling fans operated normally.

When everything checked good, we shipped the vehicle to the customer.