If it take 30 mins to get to 80C and the coolant temp gauge is accurate, then I would say it is running too cold. A new thermostat should cure the problem. The thermostat is an 87C part. That means it starts to open at 87C, and it will be fully open at 102C. As they age, they start to open at slightly lower temps and the bottom range of the coolant temp creeps lower.

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Ali Al-Chalabi

2001 CLK55
1999 Dodge Ram 2500 Cummins Diesel
2002 Harley-Davidson Fatboy
Merlin Extralight w/ Campy Record