Tire advice and outcome

(snip)

Thicker oil protects the engine better, but the default suggestion is almost always 5W30 or even 0W30 (ZEROW30). This is because thinner oil offers slightly better fuel economy. So it MAKES SENSE for a car manufacturer to suggest lighter oil be used. Most people don't keep their cars (even if they bought it USED) long enough to wear out the engine. If lighter oil is used, the car manufacturer can claim that their cars get better fuel economy. But even the car manufacturers contradict themselves on recommended viscosity for oil. The oil cap on my car specifies 5W30. The only time 5W30 has ever been in the engine is (possibly) when the engine left the factory. But IN THE OFFICIAL SERVICE MANUAL for that SAME EXACT VEHICLE, 10W40 is recommended. In fact, it specifically states that all viscosity levels from (5W30) on up to (20W50) CAN be used. Yes, 20W50. Of course, it has a chart showing outside temperature relating to various viscosity levels of oil. Basically, the hotter the temperature, the thicker the oil should be used. But if you study the chart carefully, you will see that either 10W30 or 10W40 can be used safely year-round. This is on a car with "5W30" on the oil cap.

Unfortunately, the people working at quick change oil shops aren't the brightest bulbs on the tree. They see the computer recommend 5W30 or read it on the oil cap, and think that a customer must be NUTS to want to put thicker oil in their car to protect the engine better. There's no point in mentioning the Service Manual recommendations, either. The Oil Cap MUST know more than the people who wrote the Service Manual, right? :)

I'd be highly skeptical of the claim that simply changing from 5W30 to 10W40 caused an engine to get gummed up and ruined. I would expect that changing from 5W30 to 10W40 might (at worst) significantly lower that vehicle's fuel economy. -Dave