The Northstar family of V-8 engines have been used in Cadillacs since the early 1990s and are known for leaking rear main seals. Though generally reliable, these engines can use oil at an epic rate and are difficult to repair.
The rear main seal is used to seal the crankshaft to the engine block and prevents engine oil from leaking out around it.
Cadillacs use a one-piece PTFE rubber rear main seal. Though this seal does a fine job of sealing most engines, the Northstar engine has a basic flaw that makes them leak-prone.
Northstar engines have a tendency to leak because their aluminum blocks and steel cranks expand at different rates when hot. When this is combined with inherent flaws in the seal's design, leaks are sure to ensue.
Northstar's rear main seal replacement procedure requires that the engine be physically pulled away from the transmission or removed from the vehicle because the new seal must be slipped over the end of the crankshaft.
Though arduous, replacing a Cadillac's rear main seal requires very few specialized tools. Once the engine is out, the job can be done with a flat-head screwdriver and a $281 rear main seal installer tool.
