Intake manifold at top of engine?
Need to check the 4 corners on the intake manifold. It is common for the intake to leak engine coolant.
You either need a head gasket or intake gasket.
Engine coolant leaking internally and/or externally.
There is a heater hose that goes to the left rear top side of the intake manifold and that fitting leaks engine coolant sometimes and it will run down the back of the intake around the distributor. If that fitting is not leaking then the intake manifold gasket is leaking coolant in the corners of it. REplace the intake gasket. That's all that can leak coolant on that year engine. If coolant is leaking out between the transmission and engine block then you have a freeze plug leaking in the back of the engine, between the transmission and block. Must remove the transmission and flywheel to fix it.
Can be leaking intake manifold gaskets, which can sometimes be fixed by using Dexcool coolant. Can also be a head gasket.
If you are sure that it did not freeze and crack the block, Then the intake manifold gasket is leaking. That is a common problem with the vortec Chevy engines. You need to replace the gasket with a factory Chevy gasket from the dealer.
That is a common problem with the vortec 350 engines. The intake manifold gasket starts leaking in the corners of it. That is where the water jackets are and it's only about 1/4 of an inch wide and when it starts leaking it allows engine coolant to leak into the lifter gallery and into the oil. Need to replace intake gasket as long as you no it did not freeze and crack the engine block.
That is because it is hot ( over heating ). You need to check all 4 corners of the intake manifold with your fingers to see if it is leaking antifreeze. Chevy had a problem with the intakes leaking engine coolant. There is a heater hose fitting screewed into the left rear corner of the intake and thay are none for leaking engine coolant too. You should check the water pump for leaks too.
We have had several 4.3L engines at work develop coolant leaks from the intake manifold gaskets failing.
Need to check all 4 corners of the intake manifold with your fingers and see if they get wet. Also check the heater hose's were they go into the intake and see if the fittings are leaking coolant. It is real common for the intakes to leak on that engine.
It could be the coolant overflow tank that is leaking.
The heater core has failed and is leaking engine coolant.