I have a 1994 Buick Century with a 3.1L V6. The cap on the oil reservoir calls for 5W-30 oil.
I know that the engine is full of 10W-30 oil.
I know that the number ahead of the "W" is an indication of viscosity at very low temperatures. With that knowledge and given the fact that I live in Florida, where the absolute coldest temperature I've ever seen in my 34-year life is 18°F, I don't believe this is a problem but I don't know for sure.
I'm inclined to believe that the cap is stamped "5W-30" because Buick doesn't know if the person who buys this car will live in Maine or Florida and they want to perform some level of "CYA" as it were.
So what want to know is if this is something I should correct. Should I immediately change the oil; should I change it back to 5W-30 in time with my next regular oil change; or can I just continue to use 10W-30 oil?
If additional information can help with a verdict; the engine has relatively low mileage (~98k) but it has been neglected (it was recently run for several months to a year with a leaky intake manifold gasket where coolant was able to contaminate the oil).