Question about 1999 GMC Sonoma

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The heater still won't work after I changed the thermostat on my

99 gmc sonoma

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Get a female garden hose adapter from the local hardware store. Disconnect the heater hose from behind the fan pulley and attach the hose connection. Disconnect the other heater hose behind the alternator, aim it towards the ground and flush water through the heater core. This worked on my truck.

Posted on Mar 08, 2009

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Heater blows cold air everything else works fine 1999 gmc sonoma

Posted on Nov 01, 2009

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98 s10 sonoma truck heater stop blowing out threw vent. defrost work and warm air. trun the switch to heat the truck does not work ???

Posted on Mar 14, 2009

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Replace the heater core.

Posted on Feb 12, 2009

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1992 GMC Sonoma has no heat, replaced thermostat and water pump


make sure all air is bleed from the system then check the heater hoses by touching them they should feel the same temperature if not then the heater core is plugged and needs replacing.

Feb 05, 2015 | 1992 GMC Sonoma

1 Answer

My 99 GMC sonoma with a 2.2L is not warming up properly


Possibly plugged or inerporable heater core. Possibly heater core valve (this diverts hot air through your heater system) When you flushed the block, was there a lot of contaminant? 95% of the time, cold heat means thermostat. Also there are a lot of really cheap after market thermostats, you can buy one as low as $6.00. That being said, just because a thermo is new doesn't necessarily mean it opens/shuts when it should. You can look on You Tube on how to test one in your kitchen with boiling water,.

So three basic things affect interior heat temps. Thermostat, plugged heater core/.valve, and insufficient coolant or liquid to tranfser heat. If your interior coolant (engine temp) is working normally and your vehicle reaches operating tempature according to the needle, your thermosat is probably not the cause.

My bet is somehow, your heater core is plugged so that their is not enough "flow"

Feb 28, 2013 | 1999 GMC Sonoma

3 Answers

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Hello,,You may have to go to an after market supplier and pick up a winter front for the little guy,,or put a higher temp thermostat in,,good luck..

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1 Answer

Where is the heater thermostat on a 1998 gmc sonoma


Follow the upper radiator hose. It will lead directly to the thermostat housing. THe housing should have 2 or 3 bolts on it. Remove them and then you will find the thermostat.

Oct 28, 2010 | 1998 GMC Sonoma

1 Answer

Changed thermostat heater work couple days then stated blowing cold air again


try topping the rad up ,if that doesnt work then pull one of the heater hoses off and bleed the heater

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1 Answer

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follow your basic instinct on this one ,thats how 99% of mechanics work

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1 Answer

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Check blend door motor for proper operation (vacuum operated) if necessary, detach arm from heater box and move by hand. If you have heat then, change motor! You are reaching operating temp for engine, right? If not, thermostat is stuck open... Change.

Dec 22, 2008 | 1998 GMC Sonoma

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