Intake Manifold Gasket Leaks
Symptoms
Coolant leak at the front or rear of the intake manifold. Coolant may drip externally or, worse, leak internally into the engine oil. May also cause a vacuum leak, resulting in rough idle and poor fuel economy.
Cause
The Chevrolet small-block V8 uses an intake manifold that seals to both the cylinder heads and the front/rear of the block (the "valley" area). The gaskets between the manifold and the block ends deteriorate with age and heat cycling. The RTV (silicone) sealer used in this area also fails over time.
Fix
Remove the intake manifold, clean all surfaces, and reinstall with new gaskets and fresh RTV sealer.
This is a significant job but not technically difficult, the carburettor, distributor, and ancillaries must be removed to access the manifold bolts.
Budget $200-400 for gaskets and a day's labour.
Always check for coolant contamination in the oil (milky residue on the dipstick) before reassembly, if coolant has entered the oil, the engine should be flushed and the bearings inspected.
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