Thank you guys for the above posts. They are very helpful and I will take them on.

After work today, I did the added some coolant and did the burp procedure. My next step after this is a pressure test. I did what I did today to see if the rapid changing readings on both the digital and analog readings would occur again. I am following a cheaper solutions first approach. The cheapest possibility was perhaps when this happened the other day there was an air bubble going across the temp sensors. Not sure f that would cause the rapidly changing readings but I did want to rule it out first.

I started this with the 95 LT1 P class engine cold.

1. I had to add a bit of coolant to get have it at the cold level in the overflow tank

2. the surge tank and empty so I added coolant to the bottom of the neck. I would regret adding that much later.

3. I started the Vette.

4. I then remembered that I forgot the bleed valve. I did so, and coolant appeared. I closed the valve.

5. When the thermostat opened, coolant overflowed from the surge tank. That was messy. I squared that away. Through I did not see any bubbles in the coolant.

6. I checked the heater. t worked fine and the fluid level did not drop.

7. I ran it for 5 minutes. The temp stayed at 195. The coolant level not change.

8. I replaced the cap. Shut of the engine.

I will now do 3 warms up as the FSM suggests.

My next move is to flush the system and do a pressure test.

I may do a dye test before the pressure test.

 

make sure you pull the knock sensors for a proper flush. just pinch the connectors to remove. proper torque and dope is important. I put in new came with the right dope and could not bring myself to put back 20 year old cheap parts.