Hello Paul, my VW Golf with a 1.8 litre petrol engine has a poor starting and idling when the engine is cold. The engine fans also seem to delay coming on so the car leaks coolant in traffic jams on hot afternoons. We have changed spark plugs and coolant during service but the car still acts up. What could be the cause? Akong
Hello Akong, your VW may have a faulty engine coolant sensor (ECT). This sensor monitors engine coolant temperature and helps the engine computer (ECM) to regulate or raise engine revs for cold start warm up and lower them when your engine attains normal running temperature.
The ECT sensor helps to regulate the timely switching on and off of the engine cooling fans to prevent overheating. Failure to service engine coolant every two years with a good coolant product leads to a buildup of corrosion on the surface of the engine cooling system components and thermistor switches like the ECT sensor or thermostat.
This makes them less sensitive or out rightly damages them. A good mechanic should be able to inspect and clean the ECT sensor or replace it after testing its resistance with appropriate tools.