Why doesn't that surprise me? 99 may have been the first year..... I can't really find any hard answers on that.... I know my 96 doesn't have it.....

 

Probably determined by what day of the week it was made and whether or not it was raining...

 

That would certainly explain a lot........

 

So what do u think the issue is

 

Air pocket in the heater core. Unfortunately, it is the highest point in the cooling system. (bad design, if anyone is asking me. ) You can pull the heater hoses, and back flush the system, to get the air pocket out. Flow is FROM the intake manifold fitting, to the heater core, and then out thru the hose that goes to the steel pipe that plugs into the water pump.

 

I park the truck pointing uphill, cold. Start it and let it warm up enough to let the thermostat open, revving it a few times to burp it.

 

Need a pretty steep hill for that.

 

back flush the heater core first.. there was SO MUCH crap in mine just make sure you put a hose from the core to the ground so you don't get it all over the engine bay

 

I back flushed the system and no leaks and it still isn't working. Advice?

 

Pull the little electric motor from the bottom of the heater box, just to the passenger side of the trans tunnel. It's like two screws. Of course, one of them is rather fun to get to, may need to trim a bit of carpet to get clearance.