Greetings. I currently own a Chevrolet Blazer from Venezuela, it is a 1999 vehicle. It was supposed to use 5w30 engine oil according to owner´s manual, however the previous owner was using 20w50 oil and all of the mechanics here recommend me it. The engine has 190000 Km. Which oil should I use? Should I continue using 20w50 engine oil or should I change back to factory 5w30 engine oil? Consider the weather in Venezuela is tropical, we have a standard temperature of 27~30°C. Thanks