Unusual Coolant Issue

[Don in VT]

Hi all,

This is for the coolant system gurus on the net. In the last couple of days I have noted a new a somewhat different cooling problem. My ZR is a 1990 that is box stock .

First some info.

1. Issue just started after 2 years of absolutely no problems with cooling or coolant.

2. My Tech and I have totally ruled out a blown head gasket.

3. I am using the good old and approved "green coolant".

4. Hoses are all new Samco and the WP is 2 years old.

5. There are no coolant leaks, anywhere and no coolant smell at all.

6. The system appears to be full with no air locks and the WP pulley is turning.

7. A new OEM NOS 180 deg thermostat was installed 2 years ago.

The Problem

When I start the car in the morning the temp gauge on the engine and system do not move after 3 to 4 minutes and there is no heat from the heater. When I remove the upper reservoir tank cap there is no flow in the air bleed circuit. After about 5 minutes both gauges begin to move up rapidly especially the system temp. At this point I shut the motor off and wait. I still have no heat from the heater. I go through this a few times and finally the temp will move to the correct reading and the heater hot air comes on and the car settles down to run normally for the rest of the days drive. I can shut it off and restart during the day and everything is OK until the next morning. My FSM and my gut feel would indicate that the thermostat is stuck closed but it doesn't explain all the observations.

Any help here would be appreciated.

Thanks

Don





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