I bought a swift AT transmission recently with 33k on the ODO. I am not sure what oil the previous owner was using, it wasn't from Suzuki. My mechanic suggested to use havoline 10w 30 and I went with it. When I checked the manual later it said 10w 40 is recommended. I'm a bit worried now since it's really hot in islamabad these days. Should I immediately change it to 5w 40? I have had no problems so far. What do you guys suggest?