Question about 1998 Pontiac Bonneville

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Car throws heat when first started, then turns cold

After the car is warmed up, the heat works, then 20-30 seconds later the heat turns cold. I think it is a blend door accuator that is faulty, but I need to know how to get to it to test it

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  • rodelco Dec 21, 2008

    1998 Bonneville - Outside temperature indicator flashes for about 30-60 seconds before the blend door apparently switches to NO HEAT. Any idea what the flashing indicator is telling me? Thanks.

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First of all you need to take this part of the control unit out but leave everything connected so you can see if it is moving also check to see if there is any vacuum lines off the back of it cause this will cause it also

Posted on Jan 05, 2009

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My heater blows hot for a couple minutes then turns cold. After turning it off for a few minutes and back on, it blows hot then goes cold again.


LET YOUR CAR WARM UP FIRST!! or you risk the chance of over heating and casuing engine damage. start your car let it warm up for 5 to ten minutes and then try the heat. also when you start you should NEVER have heat on right away. the heat that you feel comes from the engine. and if the engine is cold and you are trying to heat it up it will put stress on the engine and over heat. ALL cars have to wait for their heat. that's why you see peoples car running in the morning with no one in it. so when they do get in it they have heat. heat will not work until the engine is warm.

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Car does not heat up despite debater being on and letting ca run for 15 minutes


There are several things which come to mind. You have 2 complaints. A gas smell and a cold blooded vehicle.

Starting with the temperature problem. My initial concern is whether the thermostat is weak, but also that the automatic controls may be inoperable and working against you. The car is suppose to go into a temporary "cold start routine" which increases the RPM and makes the fuel rich. (This could contribute to the gas smell)

After the Temperature sensor and O2 sensors warm up, the idle is suppose to drop and the fuel mix should lean out. If the engine remains at high idle, the water pump will work faster with the engine spinning faster. Sometimes there is not a direct 1 to 1 ratio between the heat generated by the motor and the RPM versus the cooling produced. An idling engine may warm up faster than an engine running at higher RPM.

Another problem may be the Defroster setting. There are Thermal switches which are suppose to cut off the Electric Radiator cooling fans. When the Defroster is activated, some cars are built to spin the A/C compressor in the Winter. But the Electric Radiator cooling fans may also switch on as part of the A/C system. This would super cool the radiator at a time when you least want it. Check to see if the cooling fans are activating when the Defroster is turned on.

There can be 2 Temperature switches in your car. One would send the signal to kick out the "cold start routine" and the other would work the guages or indicator lights.

The O2 sensors can have heaters in them or they can just be slow. If you leave the engine idling like you do, they could foul out and be sluggish to warm up.

If running the Temperature at 80 degrees causes an additional 5 minutes of warm-up time, you may be better off setting it for say 72 and having it work sooner.

The thermal sensors are not that expensive. Work on a cold engine when changing them. Note what I said about your rich fuel mix contributing to the smell.

Please rate my info.

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My 2005 malibu 6 cyl has 54000 miles and no pior problems or warnings i went out and started it and came inside while it warmed up and when i went back out about 10 minutes later the car wasnt running, and...


many ideas lol. sounds like the fuel pump may have froze up. was the tank below 1/2/? moister in the fuel can cause this. any way to warm the car? this would be my first step

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When my car warms up the heater blows out warm but gradually gets cooler and cooler after about 10 min. It will stay cold ( about three degrees above outside temp.) It does this on cold days. And after you...


It may be the valve that controls the amount of water entering heating core but I'm wondering if your engine thermostat isn't stuck open. This is what controls the coolant temperature in your engine. It closes off while engine is off. It will remain closed after you start your car until the water warms to a certain temperature then it starts to open enough to keep your car at the proper operating temperature. If it stick open then it will take a lot longer for the engine to heat up and on smaller cars might never heat up enough for your heater. If you live in very cold climates such as where I live in Wyoming, we have to change to a higher degree thermostat so we have a good heater when it's 30 below zero.

Be very cautious here but one way you can check this is to put a piece of cardboard in front of your radiator and stop the airflow that cools your engine coolant. THIS WILL CAUSE YOUR CAR TO HEAT UP AND CAN CAUSE ENGINE DAMAGE IF IT OVERHEATS. Don't completely cover the radiator but if your heater warms up when you put the cardboard in front of radiator it's a good sign that your thermostat is stuck open and needs to be replaced.

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I would have the heater core checked. It could be something as simple as a fuse but unlikely. not likely to be the thermostat as that would make the car overheat if it wasnt working.

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1996 buic park heater starts to heat then afer a minute blow cold


it sounds like you have a blend door problem. This is located in the HVAC sysem it closes a door from cold side to hot side. sounds like a bad servo motor or a vacuum leake on that motor. Hope this helps you, please rank this solution

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Replace the thermostat, if that does not cure the issue you have a slight head gasket leak. I am a retired Ford dealer tech and this is what I have found causes this issue.

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