truck won't start and dealership said the oil is sludge i change oil every 4500 miles faithfully
All depends on the oil brand you use, also the breathing system for the crank case may have needed attention for a while. They claim oil can go as far as 8000 miles, but best results is to change oil every 3000 miles.
For city driving it's usually best to change the oil every 3000 miles.
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