Hi Moedip,

For one thing, the higher the temperature the faster the oil degrades and loses its lubricity. One has to be more conscientious about oil changes and fluid level checks (engine coolant and oil) with hot running engines. Also, heat damage being cumulative, check for operating temperature creep over time as this is a sure sign that something is going wrong. As you said, temperature gauges are not very reliable in absolute terms but they can tell you, in relative terms, if your maximum operating temperature is creeping up.

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Reno

'93 300E 4Matic
'98 Nissan Altima
'00 Yamaha Road Star Silverado