I recently had a gurgling issue, and it was a bad thermostat. It was stuck open so I could hear coolant flowing anytime I reved it up. Yours probably isn't the same issue, but I also have very poor heat still. I spent pretty much all last winter trying to get heat. I have replaced the water pump, thermostat (twice), thermostat housing, all hoses, flushed the radiator, flushed the heater core with CLR, changed the coolant, the radiator cap, and I used the Lisle fill funnel while parked at 45 degrees. The only thing I haven't done is repalce the heater core. I still have very little heat.

 

try reverse flushing the heater core only.

 

Tried that when I did the CLR flush. The heater core flows very well.

 

I thought mine flowed very well too, that is until I replaced the heater core and flushed it for the hell of it just to see the difference. Big difference, there was less pressure and more volume.

 

When I burped the 1st time I left the cap on. the second time was just the heater core with return (drivers side) disconnected to work the coolant back and forth so to speak. Heater was full heat, blower full blast, no cooling fan connected at the moment (converting it) ran the truck until the coolant was around 200f. Windows do not fog up, never have. I do have a sweet smell in the truck but when you do **** wrong and get a coolant volcano everything smells kind of sweet. Flushing the system after that was pretty simple. haha

 

Yeah, many people are skeptical when I tell them to use CLR so I just don't tell people any more. But that stuff works wonders.