Question about GMC Yukon XL

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Duh-the heater output is low-the coolant level is normal. This is a GMC product which would make a really good addition to an artificial reef, but I live too far from the coast to walk home. Bummer

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Heater core is eather stoped up or not working correctly, Check by using a clothes hanger and shove it up your a/c drain tube. This should be located on passenger side up by the firewall, Sometimes this gets stoped up. But more then sure it's the heator core. Best of luck to you.

Posted on Apr 04, 2011


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My 2005 gmc seria heater will not blow hot air

There are a number of possibilities.
First, its the level of coolant in the radiator full?
Low coolant level will cause this, because the heater is higher than the engine, so air can rise to the heater and form an air-lock.
Second, is the thermostat good?
A thermostat that is stuck open will not make heat for the heater.
Third, the control valve may be stuck or broken, not allowing the hot water to flow to the heater core.
Usually these are vacuum operated, and usually found under the hood.
God bless your efforts.

Oct 26, 2015 | GMC Cars & Trucks

1 Answer

My 93 GMC suburban overheats. I will turn on the heater and cold air will blow out. Intermittently hot air will blow out and the tempreture will drop to normal levels. Im not sure where to look first.

The thermostat is bad,replace. Also, if coolant is dirty looking, you might want to take it to a garage and have the coolant system flushed. Good luck!

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My temp guage (interior) in my 2003 sonoma goes up to about halfway, starts blowing cold air through the interior vents, then it goes back down to normal range, and goes back to blowing hot air.

First thing to check would be coolant level in return bottle and/or rad. If you have a rad cap, remove it, start engine, turn heater on and add as necessary when engine at operating temperature as needed. Wait until you see increased flow through radiator before topping up and putting rad cap back on. It may be that coolant level is just low enough to cause airlock in heater core.

Jan 28, 2011 | 2003 GMC Sonoma Extended Cab

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First check coolant level and strength. If good condition most likely stuck open thermostat, just follow the upper rad hose to the engine. Remove the throttle cable bracket to access the 2 bolts holding the thermostat housing to top of engine. Make sure engine is cold before removing, you will loss a little coolant when replacing. Other causes could be plugged heater core, with engine running at operating temperature on gage. Follow the 2 heater hoses the the right side firewall (where they go thru into cab) one should be hot and the other warm (if the outlet is cold, heater core is plugged). The waterpump and cooling fan are direct drive off the engine and not usually an issue on this vehicle.

Jan 25, 2011 | 1995 GMC Yukon

3 Answers

My heat in my truck comes and goes but the temp gauage stays at normal range

It is possible that the coolant is a little low causing the heater core to get "air locked" Check your coolant level. There could also be a problem with your water pump not able to pump correctly due to a worn or corroded impeller. This will usually cause the heater temperature to fluctuate widely with engine RPM. There is allways some fluctuation caused by RPM, but if it is a large fluctuation, it usually means low water pump output or possibly a partially clogged heater core.
Feel the hoses going into and out of the heater core. They should both be hot. There may be a 20 or 30 degree difference in temperature, but both should feel very hot to the touch. If one is really hot and the other just feels warm, the heater core is probably clogged. If you have access to an infrared thermometer, taking the temperature of the hoses is the best way to check this.
If both hoses feel "Warm" at idle and get really hot when the throttle is cracked open for a short period (20-30 Seconds ), the water pump may be the problem.

Jan 23, 2011 | 2000 GMC Sierra

2 Answers


Make sure the coolant level is full. If coolant levels are ok you made need to replace the thermostat .You can disconnect the heater hoses going to the heater core and flushing water through with a garden hose at low pressure. If the vehicle has the 4.3L engine these are quite prone to heater cores plugging up. Would try flushing the heater core first.If that does not work most likely the thermostat is causing your issue. Be sure to fill coolant back up after servicing and allow air to bleed from the cooling system.

Dec 01, 2010 | 2003 GMC Sonoma Extended Cab

2 Answers

2005 GMC Sierra 1500 - heater blows, but only cold air

Check coolant level. Check for heat at the heater hose going from water pump to heater core at firewall. Check to see that cable is moving coolant control valve from the closed to open position. Low mileage so it shouldn't be plugged heater core.

Jan 07, 2010 | 2005 GMC Sierra

3 Answers

No heat is coming from the vents.The heater fan works normally. There does not appear to be heat recirculating through system. When in stop and go traffic the heat indicater gauge goes to hot. When the...

when the level of coolant drops in the motor the heater core is the first to be without
because it sets up high
so you need to check the level
and check where the coolant is going
to make the level drop

Dec 24, 2009 | 2004 Dodge Intrepid

1 Answer

Problems at low RPM

check coolant level! look for coolant loss

Mar 21, 2009 | 2001 GMC Yukon XL

1 Answer

2004 GMC Sierra Heater does not heat on low RPM

check your coolant level on the radiator

Feb 03, 2009 | 2000 GMC New Sierra 1500

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