What is a Pattern Failure?

when i was trained at MCTI we where always taught too be weary of other things besides pattern failures, the car i drive 2008 pontiac grand prix, has a driveline and body that is well known, thousands of them are driven buy people every single day, so pattern failures are easy too find on my car…

one day we had a Early 2000s pontiac grand prix pull into the shop with a series 2 3800 engine, the customer complained “my coolant is leaking and i don’t know where it is going.” knowing my 3800s so well my friend pulled it into the shop and i said pop the hood and immediatly i pulled the dipstick and found the oil level 3 too 4 times over filled too capacity with a diareah colored mixture… and assumed that its lower intake manifold gasket or upper plenum and its gasket had gave up. well my instructor had us do a combustion leak test rather than me assume it was the lower intake manifold gasket or upper plenum and its gasket and we found combustion gasses in the cooling system and bubbles too, the 3800 in the car suffered a VERY rare failre for the engine, a blown head gasket in which the 3800 is not so well know for since its a cast iron block with cast iron heads… sadly my instructor would not let me perform the repair in which i was so excited too perform.