Quote Originally Posted by bail View Post
I was using Havoline 20w50 before and have not encountered any leak. But recently after changing it to 10w40 from shell high mileage oil, Ive seen several leaks below the thermostat area and some around the gasket cover. My valve gasket cover was actually newly replaced before the change oil. Is this a major engine problem? Ride was actually smoother after changing it to 10w40. Problem is yung oil leak. Car is corolla 1997 gli 1.6. 120k mileage.

Something about the additive not just the grade...

Oil hardening oil seals? | Passenger Car Motor Oil (PCMO) - Diesel Cars/Vans/SUVs | Bob Is The Oil Guy