I've noticed lately that anytime the RPM's go past 3000 the coolant temp drops, but as soon as I get below 3, its back up to normal again. The fault codes I got were for the knock sensor (KS).
If anyone has this issue, or even better could point me in the right direction so I can learn more about whats goin on here.
Thanks

 

You need a new thermostat. The higher RPM's are making the water pump pump the coolant through the radiator quicker. The thermostat is supposed to regulate that and maintain proper coolant/engine temp. When the thermostat gets weak, it opens to early and flows to much coolant through the radiator cooling the system down to much. You should notice this more so on the highway because more air is also flowing through the radiator adding to the cooling process.

 

ya on the highway it was burried, thanks for the help