Question about 1998 GMC Sonoma

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98 gmc sonoma heat works of and on

Its like there is no pressure in the lines going to the heater core unless u give it gas replaced line going to heater core started working now its working hardlt at all more cold than heat

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  • GMC Master
  • 2,292 Answers

All kinds of things to look at.
Start with coolant level in radiator. Very often if the radiator is low, the heater will not work, or work well, because if there is air in the system, air will rise to the top, leaving the heater core with an air bubble.
Whenever you replace any hose on the car, you must run the engine with the heater on at a medium high RPM (1500 RPM) for a while (5-10minutes) to "burp" the air from the system.
You'll need to make sure the system is full of coolant after that.
Then there could be a partly plugged radiator, a pinched or crimped heater hose, or the heater control might not be allowing the hot water to flow fast.
Be sure to test the temperature of the radiator, to be certain the thermostat is keeping the radiator coolant at near 200 degrees. A thermometer in the top of the radiator will tell you.
If you have a sealed system, you might VERY carefully feel all the hoses to determine the heat inside the radiator after the motor has been running for 10-15 minutes.
Thermostats can get stuck in the "open" position, requiring replacement before you will get heater heat.

Posted on Jan 05, 2013

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tripletauto
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SOURCE: 1996 GMC Sonoma heater core

the dash has to come out

Posted on Sep 11, 2008

dnewcombe1
  • 1564 Answers

SOURCE: Replacing heater core in 2000 GMC sonoma. Dash is

If the dash is removed you've saved about 9 10ths of the job endurance. Look around, what you believe to be, the perimeter of the heater box. I cannot, and no one else can, tell you exactly where the bolts and nuts that mount the heater box are. Therefore you must viually sixe the box and check outide in the engine compartment and inside under the dash for the mounting bolts.You'll want to start by removing the heater hoses. Then starting at the passenger side engine compartment look for a group of 10mm or 7/16ths nuts retaining the housing and remove them. Do the same inside. The housing is usually held together with screws or clips, it changes year to year. Keep a log or pix of the wires and cables and hoses(vacuum) that are connected to the housing for reassembly. You'll need to "roll" the box out from under the dash depending on how much of the dash has been removed. The core is easy to spot for is has two hoses sticking out, and, is encircled with clips or screws . Also make sure you remove the bracket around the two entry hoses if it has one. Thank you, Dana

Posted on Oct 04, 2009

  • 3 Answers

SOURCE: Heater doesnt work blows cold air, replaced

This is what I did to solve the exact same problem.I got a pump that you can hook to a drill that has garden hose connections on it.I made 2 hoses to pump into my heater core and hook to the pump. I bought some radiator cleaner at Auto Zone and put it in a 5 gallon pail with about 2 gallons of hot water.I pumped the cleaner from the pail into the OUTLET side of the heater core.(By going in the outlet side you are back flushing the core.) I put an old cloth over the top of the bucket and let the outcoming cleaner run onto this cloth acting as a filter for the dirt coming out of the heater core and let the pump run about 10 minutes. Believe me,A LOT!!!!!!!!!!! of dirt,rust etc. came out of my heater core. The heat now works excellent! Good luck.

Posted on Jan 29, 2010

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