Check your new thermostats
 

Just a tip to anyone who wants to be anal when it comes to their repair work. After almost toasting a new engine this week I'll always test my new thermostats from now on.

Was finally ready to start a fresh Olds 455 in the Delta I've been restoring for a guy. Filled it with fluids, set the timing close, battery installed, etc.
Fired her up after a fuel system issue. Initial break-in should be 20 minutes between 2000-2500 RPM.

About 2/3 the way into it the motor started getting really hot, blistering the paint on the intake crossover and the exhaust manifolds, then the upper hose blew a small hole. Shut it down and let it cool off. Replaced the hose, confirmed timing. Still running super hot. In the cold it was still hitting 210 within 6 or 7 minutes at idle.

After looking over a bunch of stuff I finally pulled the thermostat to run the car without one. Before I did that I decided to drop the thermostat into a pot of boiling water.....sure enough it was only opening about 1/3 of the way....restricting flow. This was a brand new thermostat. Never had a bad one before in my life. From now on I'll take an extra 10 minutes to check them before I put them in.

glad to here you found the issue. Its always something small that starts the problems.

Yup. You can also drill 1/8" holes in them to help protect against air pockets and full failure.

Great Idea

This FTW! Also go to pepboys and get a cheap 3 guage set (oil water and volt) gauges for like 30 bucks to keep around the shop for cars that have idiot lights....

IR thermometers FTW