I need some help/advice on a regular temp-guage spike. First, the back story. I've had my '56 Chevy for 25 years. Engine is a 327, 60-over, 1.94 heads, mild cam. The build on the engine is 20 years old, but very few miles and it runs strong -- no smoke, no oil consumption, etc. But the car has always had a problem with overheating when sitting in line. Running at speed, never a problem. Over the years I've gone from stock radiator to a big Griffin; stock blade to electric puller that runs constantly. About two years ago I had a lot of work done on the car: AC, serpentine belt system (new water pump); Classic Instruments dash insert (replacing manual temp guage). Car ran cool as a cucumber, but after driving 10 miles or so and coming to a halt, the guage goes from 190 to full hot in about 10 seconds. This usually occurs when I get from from a ride, or yesterday when I got to the local cruise night. No detonation, no dieseling, no overflow puking, etc. And, when you lift the hood the engine doesn't seem to be throwing off a ton of heat. This happened last fall and I switched from a 180-degree to 190-degree thermostat and it seems to cure the problem. I drove the can all winter (on nice days) and never had the problem. Sat in slow traffic a couple of times and the car never got above 200. Yesterday it's hot. On the drive to the cruise, the car ran at 190, including a couple of stops at lights. But, once I stopped at the cruise entrance to get a raffle ticket, the guage climbed to full hot. Drove to a spot, stopped. When I shut the engine off there were a few (three or four) little "bump noises". Not dieseling, though. Same thing on the way home -- normal temps, but in the time it took to stop outside the garage, back up a little and then pull in, the thing spiked once again. Same little "bump" noises. But, underhood seemed fine. No overflow, no hissing or bubbling, no apparent excessive heat. Sorry for all the detail, but I've been fighting this gremlin for years and I'm stumped. Thanks in advance for any suggestions.