1993 GMC SUBURBAN 1993 SUBURBAN NO HEAT

  • Tiny
  • scottymcdee
  • 1993 GMC Suburban

Heater problem
1993 GMC Suburban V8 Four Wheel Drive Automatic 131000 miles

I asked this question before in Feb 09. Since I live in Florida it wasn't a big deal. Still no heat, here's what I've tried.

It has frt/rear heat, so I by-passed the rear hoses to frt only heat. While the hoses were unhooked to the frt core, I used my garden hose on the inlet side and had full pressure water out of the outlet hose, so I know the heater core isn't clogged. I replaced the thermostat with a correct 195 and the temp gage reads 195 and lowers as the thermostat opens/closes. The radiator is full, correct antifreeze mix. Now the problem. The outlet hose of the heater core runs to a metal tube which connects to the back of the engine by the distributor. If I put garden hose pressure on this metal tube it doesn't flow. I removed the thermostat from the engine and tried it again and still no flow. What exactly does this metal tube in the back of the engine do? Is it coolant that runs through the block back to the water pump? When I touch the heater hoses they are slightly warm due to engine bay heat, not coolant. The metal tube stays cold even after a trip to the store. I'm stumped.

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Sunday, January 3rd, 2010 AT 1:22 PM

14 Replies

  • Tiny
  • Docfixit
  • Expert
  • 18,991 posts

Hi
The metal lines should be two runn coolant to rear heater core. Did you unhook hoses from rear core and connect together? Is vacuum operated heater control valve opening?
Let me know
Thanks for donate

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Sunday, January 3rd, 2010 AT 1:51 PM
  • Tiny
  • merlin2021
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The metal tube tapped into the block is just the fitting for the hose to attach to, try reaming it out with a wire coathangar, could have rust or corrosion blocking the flow. Or the impellers on the pump may have dissolved over time, it does happen!

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Sunday, January 3rd, 2010 AT 1:53 PM
  • Tiny
  • scottymcdee
  • Member

I'll try reaming the hose, it has no flow at all. Thanks.

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Tuesday, January 5th, 2010 AT 6:04 AM
  • Tiny
  • scottymcdee
  • Member

I've bypassed the tubes to the rear heat, flushed water through those lines and everything was fine. IF it gets warm outside I will ream the block tube, process of complete elimination leads to the metal tube to the back of the engine. Yes, all vacuum operated doors etc are working perfectly. The block tube is ice cold after trips around town.

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Saturday, January 9th, 2010 AT 4:46 PM
  • Tiny
  • scottymcdee
  • Member

Rear coolant line located on the back of the intake by the distributor was plugged.

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Sunday, March 7th, 2010 AT 11:23 AM
  • Tiny
  • merlin2021
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So all is well?

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Sunday, March 7th, 2010 AT 11:40 AM
  • Tiny
  • scottymcdee
  • Member

I broke the quick connect hose (like everyone else does) that went into the back of the intake manifold and scratched my head on how to fix that problem. I finally decided to get an older chevrolet heater hose connection (the one that comes out of the top of the water pump on the old chev's) I tapped the ID of the old broken pot metal quick connect due to the fact that the ID of the broken one is approx the same tap drill size. Tapped the threads for the new connector into the pot metal, used ultra black sealant, and worked like a charm.

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Tuesday, March 16th, 2010 AT 1:55 PM
  • Tiny
  • merlin2021
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Believe it or not, it's 1/2" pipe thread. Good work!

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Tuesday, March 16th, 2010 AT 2:22 PM
  • Tiny
  • scottymcdee
  • Member

I scratched my brain for a good 1/2 hour before I came up with that fix. Glad I've worked around motors back in the day and remembered that connector.

Next question. Why doesn't my electronic controller work in the dash now? Worked for 2 weeks after I fixed the hose problem previously, then the dash unit died. I have all power to the back of the unit, checked all fuses AND fusible links in the engine compartment on the firewall. Still nothing. Stumped on this electronic crap. I've got an old manual linkage controller from my 72 pickup, wish I could put that in there.

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Tuesday, March 16th, 2010 AT 3:35 PM
  • Tiny
  • merlin2021
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Do you mean the blower does not run? Or controller does not turn the blower, or switch the registers air flow?

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Wednesday, March 17th, 2010 AT 3:09 PM

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