Some common Northstar engine problems include head gasket failures, excessive oil consumption, knocking or pinging, oil leaks and no oil pressure. Although most of these issues are easy to resolve, Northstar engines are very expensive to repair, and preventative maintenance is critical.
Blown head gaskets are one of the most common problems associated with Northstar engines. Much of this is due to the type of bolts that secure the heads. They're only meant to be used once, and they expand when tightened. Unfortunately, they expand even further during an overheating condition, after which they do not return to normal size. This leaves the head loose on the block, allowing the gasket to blow.
Excessive oil consumption is another issue pre-2000 Northstar engine owners report, with some losing up to a quart of oil in just 500 miles. It's not leaking, but rather burning up in the combustion chambers, due to carbon buildup in the piston ring grooves.
After engineers fixed the oil-consumption problem, a completely different carbon buildup issue developed in engines built from 2000 to 2001. The deposits in these engines get extremely hot, causing knocking or pinging under hard acceleration.
Oil leaks from the rear main seal and valve covers are common on 1996 to1999 engines. The company developed new seals and gaskets to fix these issues.
Engines made from 1993 to 1994 are prone to oil-pressure problems. In many cases, there's virtually no oil pressure due to debris caught between the oil pump's pressure relief valve and its seat. Cleaning up the debris or replacing the pump fixes the problem.