I flushed my cooling system 3 months ago. Coolant still rusty. Hearing gurgle in the system. Noticed leakage out of cap. Replaced thermostat and still leaking out of cap. No pressure on top hose. Need help.

 

Try taking the coolant resivour cap off and see if there is flow, is the coolant moving? Coolant can become very corrosive if it is not changed often enough. In most cases it can cause the fins of the water pump to corrode away, I see this a ton on Ford cars although sometimes on the trucks. If you have no movement in the system i would pull off the water pump and inspect the fins, I know this sounds like a lot to do although if you flush the coolant and a month later it is stilll brown most likeley the fins on the water pump have been rotting away , and are starting to clog the heater core. I would drain the coolant pull the water pump and let a garden hose run through the engine to get as much of the brown out as possible. I wouls also replace ther cap. Also when you refill the coolant turn on the heat and leave the rad cap off, let the truck run untill the fliud is sucked down then add more coolant. repeat this untill the coolant is full. this will help get all the air out of the system, make sure the thremostat opens. If you have a lazer thermometer you can check the tempo difference at the heater core inlet and outlet, this should not very by more than about 10deg F. I hope this is helpfull.

 

I've ran into a similar situation before. I neglected changing my coolant for sometime and it came back to haunt me. Iended up havingto replace the water pump because of the corrosion just as 02greenF150 stated. Be proactive if you haven't been so far. Good luck with everything.