1994 suburban - rear heat issue

[slomo]

I forced compressed air and unclogged the rear heater core. Have garden hose water flow both ways. Let CLR soak for 15 minutes. Flushed and back flushed it all out.

Question is we have no hot water flowing past the firewall to the rear core. Front heater core is working okay, not great like a new car that'll burn you out fast. Lines to the rear core are cold at the firewall and all the way to the rear heater core. No hot water is making it past the firewall area.

This model has no valves to stop any water to the rear core like when running the A/C. We flushed towards the rear at the T coolant manifold that feeds both heater cores. Should be nothing stopping water flow going back.

I did air flush all the water out before hooking up the coolant lines. Do we have an air lock issue? Obviously the lines are full of air. We started the engine and allowed the thermostat to open several times. Rev'd the engine to possibly force more water back. Still nothing.

Noticed on Autozone for this Suburban, they have a standard water pump and a severe duty pump. Doesn't say you need the severe duty pump for rear Suburban heat. No other details about this severe pump. Napa and O'Riley's have the same titled pumps. Anyone have any clues?


Also we have 110 degree heat at the FRONT air ducts. Front has a new heater core with clean coolant/radiator. Do we have a water flow/pump issue here?


slomo

 

[DirkDiggler]

I have a '04 Yukon and had an issue with rear heat, but it was the electronic controller that worked the damper. It defaults to cold and was locked shut and would only blow cold air. I bought 2 new damper/actuator controls (ceiling/floor and hot/cold) and it works like a champ. I was getting hot coolant back there, but it bypassed b.c of the damper.

try this: http://www.tahoeyukonforum.com/forum/showthread.php?t=12635

 

[Chris142]

Are you sure it does not have a heater control valve below the coolant overflow bottle.

 

[slomo]

The rear blend door and controller is working fine. Rotates from H to C okay. We have no hot water back there.

slomo

 

[slomo]

Originally Posted By: Chris142
Are you sure it does not have a heater control valve below the coolant overflow bottle.


I followed the hot coolant from the driver's side radiator tank to the intake manifold to the T heater core manifold finally to the left rad tank. We found no heater control valves at all. The rear core is plumed with rigid aluminum lines mostly. Nothing in the path to stop the hot water.

slomo

 

[DirkDiggler]

try the Tahoe Yukon forum for some advice as well

 

[spasm3]

How old is the water pump? I've heard stories about the vanes being worn off to the point of hardly pumping.

 

[Chris142]

Originally Posted By: slomo
Originally Posted By: Chris142
Are you sure it does not have a heater control valve below the coolant overflow bottle.


I followed the hot coolant from the driver's side radiator tank to the intake manifold to the T heater core manifold finally to the left rad tank. We found no heater control valves at all. The rear core is plumed with rigid aluminum lines mostly. Nothing in the path to stop the hot water.

slomo
the hose off the rad should go to the heaters.if it goes to the intake its plummer wrong

 

[slomo]

Originally Posted By: spasm3
How old is the water pump? I've heard stories about the vanes being worn off to the point of hardly pumping.


Pump is 3-5 years old. I too thought about this and the possible cavitation issues. The temp gauge runs fine with the installed 195F thermostat. Never runs hot or cold so to speak on the dash gauge.

slomo

 

[slomo]

Originally Posted By: Chris142
Originally Posted By: slomo
Originally Posted By: Chris142
Are you sure it does not have a heater control valve below the coolant overflow bottle.


I followed the hot coolant from the driver's side radiator tank to the intake manifold to the T heater core manifold finally to the left rad tank. We found no heater control valves at all. The rear core is plumed with rigid aluminum lines mostly. Nothing in the path to stop the hot water.

slomo
the hose off the rad should go to the heaters.if it goes to the intake its plummer wrong


Makes sense to me too. I would like to see it hit the heater cores first then the intake manifold.

slomo

 

[Chris142]

The water comes out the intake.goes to the heater(s) then returned to the rad. I'm 99% positive it should have a heater valve under the air intake/coolant bottle area.

Is it possible that someone goofed the hoses up?

 

[slomo]

Originally Posted By: Chris142
The water comes out the intake.goes to the heater(s) then returned to the rad. I'm 99% positive it should have a heater valve under the air intake/coolant bottle area.

Is it possible that someone goofed the hoses up?


Goofed, don't think so. You should have in and out hot water flow to each heater core. Some reason the water pump isn't strong enough or we still have some percentage of blockage in the rear core. Again rear core seems to flow fine with a garden hose duct taped to it both ways. The exiting water went say 1-2 feet with the garden hose attached.

slomo

 

[edwardh1]

post pix of the hoses?

 

[WobblyElvis]

I have a manual that shows a "water shutoff valve" and a "harness, aux. heater water shutoff valve" on top of the right front inner fender.

 

[slomo]

Originally Posted By: WobblyElvis
I have a manual that shows a "water shutoff valve" and a "harness, aux. heater water shutoff valve" on top of the right front inner fender.


I will trace the hoses out again. We had the air breather and ducting off that goes to the fender. Didn't see any water control valves in that area or towards the firewall on back. No valves in the rear plenum either to control water. Will check the right fender area as suggested. All we had is two T manifolds that feed each heater core, front and rear.

I'm wondering if the water pump isn't strong enough in pressure to pump it all the way back to the rear core? I'm going to pinch off the front core so all the pressure will divert to the rear core. Hopping to get water flowing to the rear core that way.

slomo

 

[Chris142]

F Y I. The water pump pulls coolant.it does not push it

 

[slomo]

Originally Posted By: Chris142
F Y I. The water pump pulls coolant.it does not push it


Wouldn't it push and pull?

slomo

 

[slomo]

Originally Posted By: Chris142
F Y I. The water pump pulls coolant.it does not push it


So why do they call it a water pump then?

So you're saying we should be calling them a water pull? Next time I go to Napa I'll ask for a water pull.

slomo