Why might the heating system in a 1998 GMC Jimmy stop working?

Answer 1

Blown fuse, blower motor, or switch. IF the Heater Control Valve isn't getting Vacume or 12 Volts(IF Electric-IF the Heater Core is Blocked or Heater hoses Kinked-OR EVEN a bad ACTUATOR DOOR-I Don't know if u are talking a Blower Problem or WATER Circulation Problem. MY Jimmy stopped producing "heat" through the vents. The fan worked at all speeds, but all it blew was cold air. I actually did not notice until winter hit. If this describes your problem try flushing your cooling system and replacing your thermostat. I tried just flushing b/c the thermostat looked upon visual inspection. I get hot air now after I put a new one in. After losing hot air in December '04, I discovered that my 1998 Jimmy had coolant grit blocking the heater core on the inlet. Removing the hoses from the core and backflushing did the trick. The guys at the local Jiffy Lube flushed the entire system and converted me to green coolant. I've been OK since (4/2005). After having this problem: Even during 2 hour drives the engine temp needle wouldn't move and therefore no heat in the cabin for 2 years in my 1998 GMC Jimmy w/ 4.3L V6 Vortec 4WD, and getting not so good mileage (about 9.5-11 mpg) I turned to the old owner's manual (something I or any other mechanic would rarely do!). There in the scriptures lie the answer 87 OCTANE!(Mid-Grade) My Jimmy now heats up to normal operating temperature within minutes despite the cold days of Colorado winter and costs me a lot less at about 14-16.5 mpg average fuel economy. I've noticed that most Jimmys don't have the digital fuel economy readout but mine has shown me what a difference 10 cents at the fuel station can do and also has the side effect of comfort in the form of heat. So if your SUV requires a higher octane fuel (read the owners manual), then it really, I mean really, requires it. (4/2006)