For the longest time I had been having problems with the heater (i.e. no heat output). After several attempts at trying to fix the heater:
1. Check heater vent flap operation (airflow on max heater setting tested ok)
2. Repl restrictor valve in coolant line
3. Coolant flush
4. Repl water pump (was leaking anyway)
5. Flush heater core
Still no heat output. The final push was the result of having to refil the coolant daily; I would lose about 1/2 cup a day.

Took it to Mr Goodwrench. The shop initially could not find the leak because the cooling system pressure would hold up as long as the engine was hot. They had to do a pressure test of the cylinders to find the leak; one cylinder was lower (however, coolant did not leak into the cylinder - plugs checked out clean) Found out that the gasket between the intake manifold and the heads was leaking.

Unfortunately, this fix was very expensive and time-consuming (as you would expect). I guess it's probably due to pushing the ol' LT1 to the red-line......

Anyway, now it's fixed and heaters working fine. What an ordeal!

 

How the intake manifold to head seal had anything to do with the heat or cooling system is beyond me. There are no coolant passages in the LT1 intake manifold.
Methinks something else got fixed in the process...

 

agreed

I wonder if it was a leaking steam pipe seal............

 

That a fact???! I was told that the coolant was leaking from one of the coolant jackets in the block through a gap in the gasket. They had to remove my intake manifold and send it out to check for cracks (luckily none were found).

To clarify on the approx location of the leak - The leak caused coolant to drip onto the O2 sensor attached to the driver's side exhaust header (I got the O2 sensor temp out of range DTC).

 

If they told you coolant was leaking from a gap in the intake to head gasket, they lied. It is not possible. There are no coolant passages in an LT1 intake manifold (it's not like an SBC intake). If it was a head to block gasket, that would seem more feasible. Perhaps it was the head they sent out for a check.

 

Are there coolant jackets in the heads? Or is it one solid block?

I guess they didn't want to give me the detailed answer & I didn't dig deep enough....

Thanks for the info.

 

The head has coolant passages.