My car takes 10-30 oil and the guy gave me 10-40 will something go wrong
No,it wont, hurt it,.
The only thing you might notice is a slight drop in fuel mileage due to the higher viscosity at running temps, it will not hurt your engine. My old rig is suppose to run 5-30 but with the high miles on it I run 10-40 year round, it has better oil pressure warm and cold, mileage sucks on it anyway so that not a concern.
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