Any ideas on what could cause random temp rises. Normally gauge is at about 8 o'clock, but lately will rise to 11 o'clock then after about 15-20 min, drop back. At first I thought it was thermostat and local shop diagnosed as same. Replaced but still getting temp spikes. Fans are turning on normally and system fluid is full. Any thoughts (pump?). My Max is an '01 w/113k miles.

Thanks

 

Through Air bleed after filling coolant is necessary. Air pockets fit your picture... see for the proper procedure - clic via top left 'Favorite Links' below. General bleed is driving one hour over 2k rpm with heater hose bleedin/dripping continuously.

Pump may also fail, but that problem would be constant.

If main hoses collapse or their inner lining collapse, temporary blockades may form. Very seldom.

Edit: Funny how one ring missin changes all... should be --->"Thorough Air bleed after...

 

Thank you. I will try your suggestion and report back.