I have a 96 F350 crew. Up until recently it was starting fine. I know that it needs to be plugged in during the winter months but, it is not starting when the temp is below 45F. Also, sinse this started my mileage has gone from steady 17 mpg to around 9 mpg. I have 77k miles on the truck and am wondering if I might be having a problem with the glow plugs ??? I heard there is a cylinoid at the top of the motor that supplies juice to the plugs and it may be suspect...