Can you? Yes. Should you? NO! Use exactly what Mitsubishi recommends and that is not 15w40.
THE GAP IS POSTED ON A STICKER UNDER THE HOOD JUST ABOVE THE RADIATOR.
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No. It's not interference engine.
the speed sensor for 2004 Mitsubishi Galant is located on the front case of the transmission output shaft and speed sensor. It is approximately under the hood to the left of the engine.
The strainer valve on the Mitsubishi Galant 2004, 2005, 2006 models is located next to the engine manifold.
Try here: http://consumerguideauto.howstuffworks.com/2004-mitsubishi-galant-3.htm Should be the same.
Low refrigerant? Blown fuse?
Safely jack the car up, remove lamps,replace bulbs.
The problem is probably the rear wheel bearings
Use an OBDII code reader or a scan tool or try disconnecting the battery for a while.