Coolant temperature variability/failing rad?

[Click]

So to drag an old thread to life, I recently replaced my rad and fan clutch. Nissens rad and Behr clutch. It almost always stays similar to the first pic now.



Going up long hills it will cover the middle mark but does not go past it like it did previously.

[jlevie]

In 50F ambients and with the car traveling at speeds of 35mph or faster a rise in engine temperature under load and then the temperature going back down when the load is removed sounds most like a bad thermostat or clogged radiator. Since the thermostat has been recently replaced, I'm going with a clogged radiator.