How long after you start the truck does this happen. Also, how long does it bounce between 190-200, and how long does it take it to bounce between the two numbers. Have you had any overheating problems? If you increase engine speed, does the temp drop? Is it a new thermostat? Sorry for all the questions, but I'll need some more info.

If I let my 250 idle for a while then the temp will increase to 200 or so, but it doesn't bounce back and forth. Also, she only does that if she's been idling for about 20 minutes or more. Good luck. John.

'68 C-10 - 250 with Edelbrock 600cfm 4 barrel, Offy intake, Hedman headers and true duals, HEI, MSD 6A box, relocated gas tank
Soon to have: T-5 tranny