October 19, 2011New on here so not sure if this is in the right category,but I have a `91 silverado 350 tbi 4x4, my truck temperature max`s out then drops to normal. I installed a fail safe thermostat (190*f) twice, replaced every coolant sensor even the gauge itself, and the temperature never stays constant. I`m not sure why it wont stay normal. Im completely stumped as to why it fluctuates up from 260 degrees back down to 200 degrees. Any info that may help is greatly appriciated.