Temperature sensitive transmission
I have a 2001 Vauxhall Astra 1.8 16v Elegance automatic with engine type Z18XE and have had to take it to a Vauxhall agent on two occasions with overheating problems. The agent has informed me that there is no fault. Nevertheless, in very hot weather, the transmission is lumpy and tightening up, while the temperature gauge reads well over the halfway mark, although not boiling up. The vehicle has now done 90,000 miles.
I have noted below everything I have done in the past:
Full service every 12 months since new. Oil and filter changed every six months. Transmission oil flushed every 12 months. Radiator flushed six months ago.
Coolant changed every two years.
Thermostat, water pump and cambelt
changed two years ago.
New ECU three months ago.
George Green
Although you say that the thermostat is only two years old, this would be the first candidate to check. I have known genuine thermostats to fail after a few months and if the thermostat is sticking it can cause the symptoms you describe.
I’d also check the operation of the cooling fans. It may be that one or both of the cooling fans are late to come into operation and are allowing the coolant temperature to rise further than would be desired. If this is the case, the problem may be due to the control module or one of the fan relays. It could also be the case that the coolant temperature sender is reading incorrectly and not triggering the fans at the correct temperature.
All of these points should be easily checked using diagnostic equipment to ensure the system temperature senders are giving the correct info to the ECU.