Time to start a WATERGATE commiseration post:
Dang found this one in our own back yard:
Engine Overheating with Vortec Heads
...The temp gauge in the car is showing above 220...
Still having overheating issues (vortec swap guys help!)
... Could it be a communication error between the 76 gauges and the newer temp sender unit I had to get, due to size differences?...
Newly rebuilt 350 with Vortec heads - overheating
...The main issue I have is it runs for 10 minutes or so and then starts to get warm...
Vortec heads running hot! Need HELP ASAP!
I just put some 350 Vortec heads on my 94 block, and the problems are...
VORTEC HEADS: BELIEVE THE HYPE?!?
Just remember that the Vortech heads are not drilled and do not have internal water pump bypass passage like the older small blocks. This is the bottom hole in the block under the lower water pump bolt on the right hand side. Without that bypass, you can have overheat issues. You simply need to run an external bypass like a big block on any small block using Vortec heads from the front of the intake near the thermostat to the water pump. Without it, there is not enough circulation of hot water passed the thermostat to make it operate correctly and the heads will get hot and the thermostat won't open soon enough.
Look at any stock Vortec engine and you will notice there is an external hose from the intake to the water pump. You need that external bypass on any engine you use Vortec heads and a thermostat.