Temperature spikes?

[cdk348]

Hello. I'm having issues with my motor temp spiking 40 degrees or so in a few seconds and then back down to normal. I have noticed that some times the motor will heat up very quickly from cold but the temp keeps going up and never drops. During this occurring both hoses are full. This is my second thermostat and it still happening. I have a 350 with about 2k on it with a new radiator, new edelbrock water pump, new fan and fan clutch and new 160 deg thermostat.