Summary:

I noticed last week that the heater was no longer blowing hot air. I turned it on an off a few time and adjusted the temp controls. No luck, air blowing just cold air.

I then checked the over flow tank and noticed that the coolant was at a higher level then normal. The truck was stone cold so I opened the overflow tank and the system was still pressurized. Odd...I quickly closed the overflow tank.

I drove the truck for a couple more days and "thought" the waterfall was back and still no hot air unless...I brake hard.

Checked the overflow tank again this morning and even more coolant was in the tank. I opened it, truck was stone cold, and tons of pressure.

Symptoms:

No hot air but, fan is blowing (unless I brake hard)
Waterfall sounds
coolant system pressurized when truck is stone cold

Thoughts are something is blocking the heater core or there is a blockage in the heater core itself. I plan on taking a look this afternoon.

Any thoughts?

 

I had the same issue on the panty dropper. When the water pump went out, it messed up the factory thermostat. I flushed the heater core and it was fine. Ended up having to get a new thermostat and that fixed the problem. Was pissed that it happened but it's a rover. What more can I say. Hopefully it's something that simple on tricky dicky

 

I have replaced:

Coolant Pump about 1k miles ago
Thermostat 400 miles ago

And flushed the system twice, this issue has just started so I am perplexed.

 

my thermostast was less than 200 miles old but the water pump went out and somewhow screwed it up. If you have a cheap replacement one, I'd try that then go from there

 

There are air flaps inside the heater assembly to distribute/mix hot and cold air. Most likely its stuck and wont mix air. When you brake hard, the flaps opens up and release the hot air to circulate and when you move forward it closes back. Just my theory. Never had that problem yet.
Check also your reservoir cap. That has to release pressure in some point. Your system must be totally sealed no room for expansion for pressure.

 

Update

the heat will start while under load

i started the engine and got it up to temp. The heater was blowing cold air. I reved the engine up and watched the coolant temp drop and hot air started to blow. As soon as I let the truck idle, coolant temp went up and heater started to blow cold air.

is this thermostat, heater core, or blocked coolant line?

 

Turn your a/c controls to Econ mode and warm the engine up. Feel both hoses going into the heater core. If one is hot and the other isn't, it's blocked. If they are both hot them it's most likely gonna be the thermostat on tricky dicky. That's how I found my issue on the panty dropper. I knew it was getting coolant there and the hoses were getting hard but the thermostat failed on my and wasn't allowing it to recirculate through the system. The other hoses were seeming to be a bit firmer than they should be too

 

I'd do a bleed procedure, stone cold, release the pressure, raise tank, crack bleeder, that whole thang. I get a slight hiss when stone cold & opening the cap, but I agree there shouldn't be much pressure in there. Is the overflow tube blocked?

On the flipside.. maybe somewhat related... I turn the heat OFF, and it still comes out of the vents (mostly the foot vents, at about a fan speed 1). Any clue on that?

 

I was running the heater on ECON. I did check both hoses and the hose on top going down was cooler. If it is blocked, why does it work when I rev the engine?

I am doing a raised tank bleed procedure. Waiting for engine to get cold. overflow tank is raised. Overflow tube is not blocked as coolant escaped out of it when I unscrewed the cap the other night.

 

I would think it works when u rev it BC the temp is rising n the wax is starting to melt n allow the thermostat to open. I'd almost be willing to bet that's your problem. When you flushed, something could've made its was out n messed up your t stat.