I have a 1993 Chevy k2500 5 speed with a 5.7L engine. My problem is that when I start the truck after about 5 mins of driving it over heats to a little over 200 then drops back down to proper operating temp. This happens every time I start the vehicle. After the temp drops back down it doesn't matter how far I drive it will not over heat again until I turn the truck off and restart it. The fan seems to be operating properly. Could it be the thermostat? When it is over heating it is causing the coolant to boil over and out the radiator cap so I have to refill about once a week depending on how much I'm driving. Any help would greatly be appreciated. Thanks in advance.