Can changing motor oil adversely the performance of my car?

Question

I have a 98 Mustang, and I'm supposed to get 5W30 oil in my car. I had been doing that, but I switched to someone else and didn't specify what kind of oil I needed; they put in 10W30. They have been putting 10W30 in my car for about a year and I just noticed. I want to know if it would be worse to keep getting the 10W30 in my car, or should I switch back to the 5W30?

Answer 1

10w30 has slightly more drag than the specified oil but will do no damage,for best performance use 0W 30 or 40 if your loading the engine heavy

Answer 2

not really, 10/30 is for the most part better for your car because it is thicker and coats better.  5/30 is better in the cold because it flows better at first because it is thinner

Answer 3

You are best off to stick with (or go back to) the recommended viscosity for your car.  It may not actually affect your performance as there is really a range of viscosities that can be used depending on climate, and on other factors.  On the other hand, there are certain engines that are very dependent on having the right viscosity, and a thicker oil like what you have been using can keep them from being properly lubricated and wear them out faster or keep them from performing as well as they should.