Now It's My Turn for Help

[Roscoe]

I am having a serious overheating problem which just started last week. Here is a chronology:

Thursday evening: Nice and cool. Took the car out. I was out on the interstate and noticed my temp gauge was pinned! Made it back home with the cap screaming like a tugboat.

Friday: Checked the water and topped it off. Idled the engine and it seemed fine for 25 minutes or so. Shut it off and let it cool. Checked the water level and topped it off. Started it and ran it up to 150 deg. Took it out to the interstate. It was running between 150 and 180. Ran it through the gears getting on the highway. Just after that the gauge went up as fast as a gas gauge when filling the tank. Made it home again with the cap screaming.

Sunday: Pulled the water pump and it seemed fine. It is a Milodon high volume aluminum pump. Everything appeared ok. I pulled the 160 deg. thermostat and cycled it in boiling water five or six times. No problem.

I backflushed the radiator and block and there appeared to be no obstructions.

Monday: Spoke to Milodon. They said it could be an air pocket and to make sure when I fill it to have the car on an incline and check it once or twice to top off.

Tuesday: Re-installed the water pump and a new 180 deg thermostat. Filled with water. Jacked up the front of the car and continued to fill. Started it up and kept topping it off till I felt it was full. Idled it for a bit and it went up to 180 deg. Shut it off and topped it off again. Installed new Stant 25 lb racing cap.

Took the car out on the highway. Initially ran at 180 deg for about 4-5 miles. Made a U turn and ran gently through the gears. Watched the gauge drop from 180 to about 160 and then, suddenly, shot up to 250 in less than 2 miles.

Any ideas,
Roscoe