My 07 Civic has 150,000 miles. The manufacturer recommends 5w20, but for the most recent oil change, the mechanic used 5w30. I assume they just did it because it was convenient, but I am wondering if it is actually a good idea to go for a thicker oil at this point. The car is getting older. The 8th gen. Civic is prone to engine problems, and I live in a hot climate (summer highs regularly exceed 100f (38c)). Any thoughts?
There should be a chart somewhere in your owners manual that shows what viscosity oil to use at what temperatures. That said, running 5w30 in an engine that calls for 5w20 isn’t really going to hurt anything, but you might notice a small drop in fuel economy.
As anecdotal evidence, my old Subaru called for 5w30 and once I started having to buy my own oil (the shop I was working at would let us change the oil on our own cars for free twice a year) I was able to get Rotella T in 5w40 at a discount, so that’s what I used. When I was running the Rotella I was getting 25ish miles to the gallon in mixed highway/city driving. When I switched jobs and was able to get 5w30 for free I started using that and my car started getting 27ish miles to the gallon with no other change in my driving habits. Take from that what you will.