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Overheating Trouble shooting

2003 GMC Sonoma. New thermostat, self installed last week, not losing coolant, hoses original but look good, no noise or leak from water pump. Gurgling noise from heater core on cold startup. Radiator cap seems to be holding pressure. Never been flushed. Changed oil / filter just last week. Radiator fan is spinning.

The heat works as normal until the truck has been up to normal temps for a few minutes. When at a stop, the heat stops working and the temp rises pretty quickly. Once I start moving again, the overheating stops and temps go back to normal. Not sure if the heater works again while moving again. Haven't paid attention to that. Just noticed this in past couple of weeks, since the outside temps have gotten into the 90's.

It seems to logically be a circulation issue. What would cause the heater to work for awhile and then stop once the vehicle is thoroughly warmed up? My first instinct is the water pump is not working correctly- but there is no noise or leakage. Could it just need a flush or could it be a air bubble in the heater core (causing the gurgling?).

Stumped,

Joe

Reply to
Joe
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Sounds like you have air in the system. Did it do it before you changed the thermostat!

Reply to
twisted

Yes, that's why I tried changing it out. Have been hearing the gurgling for a few months, but the heat always seemed to work.

Reply to
Joe

Air in the cooling system. Common problem on the S Series if you don't burp it.

Easy way to burp it is to park it with the right front elevated (so the radiator cap is higher) I use a handy bank but a curb should work. Now with the engine cold fill the coolant to the top. Now fill the overflow to the HOT position. Close it up and start the engine. Wait until it gets up to temp and shut it down. Now let it cool a bit and then check the levels again. Add coolant as required.

Make SURE you have a good cap so the siphon works the way it should as well. Should be all set. IF you are running DEXCOOL take care of this NOW, Dex does not like heat and air combined in the system, causes sludge build-up.

Reply to
Steve W.

Air was the problem. Thanks everyone.

Reply to
Joe

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