I change the oil for my girlfriends 96 Camry V6 engine w/ 10W30 all the time. We get the Chevron dino oil since it's cheap at Costco and has good oil analysis results. Last time she was at Costco I wasn't there and she bought a straight 30 weight oil which I put into her car w/o thinking. Now on the next oil change I noticed!! So a straight 30 weight has been running in her engine for 3000 miles (she has about 105,000 miles now) Is this OK to for the engine?