Overheating

Hi and thanks for using 2CarPros. Com.

What you have described indicates that the cooling fans are not turning on. At highway speed, air circulates without the fans. When stopped, there is no longer circulation and the fans should turn on to produce circulation.

First, I would check to see if the fan motor is working. You can make a jumper wire and supply power directly to the fan motor (once it is unplugged from the vehicle). If it works, the next thing I would recommend is to check the cooling fan relay. Simply switch the relay with a different relay with the same part number in the relay box. If that does not change the problem, suspect the coolant fan control thermal switch, which is located in the lower left part of the radiator. Here are the directions for testing one:

Testing Procedure

Place sensor in a suitable container of liquid that contains a thermometer an may be heated and cooled.
Connect a suitable ohmmeter or continuity tester to terminals one and three of the sensor to test the 1st stage circuit.
Heat liquid while observing thermometer and continuity tester, circuit should close between 92-97°C (198-207°F).
Cool liquid while observing thermometer and continuity tester, circuit should open below Approx. 84°C (183°F).
Connect continuity tester to terminals two and three, then repeat above procedures to test 2nd stage circuit, noting the following:
Second stage circuit should close between 99-105°C (210-221°F).
Circuit should open below Approx. 91°C (196°F).

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Let me know if this helps or if you have other questions.

Take care,
Joe

Hi.

If the same codes are returning, chances are it is not the sensor but rather a rich or lean fuel mixture, partially plugged catalytic converter, bad wiring to the sensor. If your friend has a scanner that will read VAG codes, it should be able to read real time/live data. If that is the case, ask him to check short term fuel trims. They should hover around 0. Let me know what you find with that if possible.

Now for the cooling, since the fans are working, there has to be a different problem. Since it happens regardless of the fans running, either you have a partially plugged radiator, bad thermostat, or the water pump itself is bad. I have attached a picture of the thermostat for you to see. If you decide to check or replace it, here are the directions for checking to see if it is working.

https://www.2carpros.com/articles/how-an-engine-thermostat-works

At this point, if you have not already, I would suggest replacing the thermostat and flushing the cooling system. You should inspect the water pump for play or damage to it. If you decide to replace the pump, it is an involved process. It requires removal of the timing belt. If you choose to do that, let me know and I will provide you with the directions.

Let me know what you find. I am interested in the codes and if the cooling system has ever been serviced.

Take care,
Joe