Heater woes

I'm having difficulty diagnosing my heater (no heat) problem. Have an 86b2k ext cab and noticed I wasn't getting any warm or hot air in the cab. I did have a slight leak at the stat housing which was rectified when I put in a new stat 180 deg earlier this week. Cranked it up and ran it adding new coolant when I noticed something that got me puzzled. After the initial opening of the new stat I refilled the radiator and never saw it cycle again even after watching it sit idle for 30mins. Gauge works but I've never noticed it get to even half way in the range. Today I checked the control mechs and didn't find an issue; however, I didn't pull the cover from around the evap to inspect though. Been down that road this past summer was a pain but I did get the evap clean and the blower too. Lots of air flow but no heat. Also today I reverse flow flushed the heater core and it was nasty. Reinstalled and began to refill the radiator. Again after the initial stat opening I never saw it cycle. It pulsated up and down like it was going to but I never noticed it actually do it. After another half hour of idling and watching I checked the hoses in/out of the heater core and they were cold. I've begun to think maybe the water pump but the truck doesn't run hot. I also think maybe some kind of blockage in the circulation to the heater core. As I understand it the flow goes from the pump into the block up into the head then into the intake manifold. From there into the core and back into the pump. Is it likely the blockage is in intake manifold? If so, how's the best way to determine why I'm not getting flow in or out of the core? Is there another possibility of what might be wrong?

If the pump were the problem then would I still have the initial cycle of the stat opening and flow from the rad into the block?

maybe the cable for the heater valve has broken. You should be able to see the stem of the valve move up and down when you turn the dial on the dash.

I checked all those connections from the drivers floorboard and all seem to be working (ie. they move/rotate when the all the knobs/levers are actuated). Nothing seems to be damaged with the flappers because as I move them I hear them moving on the inside.

Does anyone know what the purpose of the small 3/8 inch size metal pipe running lengthwise down the side of the block under the intake manifold is for? My model has that pipe which is connected to the water pump just under the stat housing running back toward the firewall. I'll try and get a picture of it and post it.

Okay I just looked at it and it is connected at the stat housing runs under the intake and is T'd into the pipe running underneath the exhaust into the water pump. Now I'm really confused because that connection seems to completely bypass the whole system of going through the block, head, intake, and heater core cycle.

If the hoses at the firewall are not hot after running 10 full minutes (not idling), then your issue - or first issue - is that the engine is not producing heat to the heater core, so concentrate on that.

1. You can rig up a garden hose into the heater core at the firewall and confirm that the flow comes out the other tube.

2. The small bypass circuit underneath on the passenger side of the engine should be fine if nothing leaking. I doubt that the water pump is the culprit. I suspect that the thermostat is stuck in the open position, these engines put out a lot of heat. I use a Stant 192/195F thermostat in my B2200 and 2 weeks ago measured my heat output at the vent at 135°F after 2 miles of driving.

3. Very important on these engines is to bleed out ALL the air from the cooling system. I jack up the front end, keep the cap off, run the engine with heater on for 1/2 hour and keep topping off with 50/50.

Good new guys I found the culprit today. The issue was a blockage in the nipple of the intake facing the firewall. I poked and prodded it scraping as much of the gunk buildup from the inside of that nipple did a little flush and reinstalled the hose. That got things moving through the core and I had heat. I still think something else could be going on though because didn't get real hot in the cab, but this is at least a start and better than no heat. The truck isn't a daily driver so not a supper big rush.

Well, taking care of our nipples IS important !!!

"That got things moving through the core and I had heat. I still think something else could be going on though because didn't get real hot in the cab, but this is at least a start and better than no heat."

Still drive it 10 minutes and feel the connections at the firewall to/from the heater boxes. I'm still thinking you need a new 192/195 Stant or Mazda thermostat, and/or good purging of all the air out of the system.

Changing from 180F to 192/195F thermostat on mine really boosted the heat temperature.