My heater on 2002 olds silhouette blows cold. from cold start water temp heats up properly. get slight warming in car but then blows cooler

thermostat or low coolant

its VERY likely that your heater core is getting stopped up.

The heater in your car works by circulating hot water from the engine into a copper or aluminum pipe coiled up in the dashboard. The heater/airconditioner's fan blows across it and the hot air comes out of the vents. This is why the heater doesn't work right away when you first start the car. It usually won't work until the hot/cold needle in the gauges is starting to rise up.

If your mechanic recently replaced the thermostat, its possible that there is air in the system which will result in less antifreeze in the car than it should be. If this is not the case, the heater core is probably stopping up and will require expensive replacement if it cannot be flushed clean.

Check to make sure the car is full of antifreeze IN THE RADIATOR, AND THE OVERFLOW JUG. Please be very sure there is NO AIR in the cooling system as well.

Scott

To troubleshoot this types of problem,click the link below :----http://howtobyme.blogspot.in/2012/02/heater-blows-only-from-defrost.html
--------Go through the procedure to confirm the issue.

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Engine Overheats and heater blowing cold?

http://howtobyme.blogspot.com/2011/11/engine-overheats-and-heater-blowing.html

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Heat blows cold on drivers side and hot on passenger side?

http://schematicsdiagram.blogspot.com/2011/12/heat-blows-cold-on-drivers-side-and-hot.html

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No heat on car? http://technoanswers.blogspot.in/2012/02/no-heat-on-oldsmobile-silhouette.html

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Heater blows intermittently and temp gauge goes erratic? http://technoanswers.blogspot.com/2012/01/heater-blows-intermittently-and-temp.html------------Heater blows cold? http://schematicsdiagram.blogspot.in/2012/02/heater-blows-cold.html
---------Car heater blowing warm, but not hot air? http://schematicsdiagram.blogspot.com/2011/12/car-heater-blowing-warm-but-not-hot-air.html-------- Heater/AC blower motor not working?

http://technoanswers.blogspot.in/2012/02/heaterac-blower-motor-not-working-on.html

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A/C, heater, defroster fan, not working? http://technoanswers.blogspot.in/2012/02/ac-heater-defroster-fan-not-working.html Heater problem? http://technoanswers.blogspot.in/2012/02/heater-problem-on-isuzu-trooper.html---------

This will help.Thanks.

Just saw your second posting, so the temp is still above normal. Could the sensor
that controls the fan be not reading the heat properly ? The antifreeze/coolant
issue could still be relevant, so I will re-post that info. Tho.
Electric cooling fans will sometimes come on after a vehicle is parked,
(It actually heats up when stopped), but not when it is rolling down the road
because the movement is applying some cooling effect to the engine.
\
If the engine is not actually overheating, then the fans may be working
normally. Also, make sure your water/antifreeze mix is correct by using a
specific gravity tester. It is a tube with 4 or 5 balls, some of which will float
to give you a reading. Contrary to popular belief, More is not better when it
comes to antifreeze/coolant. It needs water to work properly. Too strong a
mix will actually make your vehicle run cold so that the temp sensors and
heater will not function properly. The engine will not achieve proper operating
temperature and may actually damage some of the components by running
it cold, affect timing, spark, etc. This could also cause the symptoms you
describe. The engine would not actually reach the proper heat threshold
until you added the extra demand of the AC heat transfer. But the first criteria
would be whether the engine is actually overheating / or in normal range .
It may be that the colder weather is allowing the sensors to come on a little
later, warming the engine and heater components a bit more than they would
in warmer weather. Would be good to know what the actual coolant temp is.
Could check that with a guage, and also check to see what temp thermostat
you are using. 195 degrees in the winter would be better, 165/180 or so in the
warmer months

Sounds like the heater core needs to be flushed .. I have had to do a few of them lately.

A/C LOW ON REFRIGERENT? Or temp blend door slightly open! Note if fresh air setting or recirculating modes help or hinder the temps?

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.

Unless you have symptoms of over-heating, I rather doubt that your water pump is a problem. I recall that my water pump had a metal impeller (1992 C900); I haven't heard of a plastic impeller on a Saab pump before. (Most pump failures are the bearing seal, and the pump leaks coolant) If your temp gauge is slightly low (and was OK before) I'd rule out water pump issues.

You might have one or more of the following issues:

1. did you use a Saab thermostat? The Saab stat has three stages (no flow to rad - cold; flow to rad and heater core - normal operation; and no flow to heater core, full flow to rad - overheating) that most after market stats don't.
2. did you use a low temp stat? this opens at about 82 deg (rather than 89 deg), and will run cooler during the winter, hence you gauge will show lower than the mid point. The big benefit is that your engine won't overheat during the summer (a very good thing!) with the low temp stat.
3. has your rad and heater core been flushed recently? If the heater core is obstructed flow will be reduced and the heater will run cool. Feel the rad and heater hoses when your engine is warm; if heater hose is much cooler than rad hose with heater temp set to max, then core flow is likely restricted, or valve is not moving much from the shut position.
4. is you vacuum tank properly connected and are there no leaks in the vacuum piping? The tank is in the driver side rear wheel well below the trunk deck on a convertible, and in the passenger side front fender area on the other cars. It's a white bottle with one or two hoses connected to it. If not properly on, your vacuum operated heater flaps won't move. Does the air distribution knob make sucking or hissing noises when you set it to different positions? If not, check the tank connections, look for vacuum line leaks, then suspect the vacuum valve behind the distribution knob.
5. Lastly, the shaft connecting the temp control knob to the valve behind it may not be properly in place. This can be inspected, and adjusted if necessary, from the speaker/vent cutout on top of the dash. Make sure you re-connect the black flex hose to the air vent tube, or you'll get no defrosting afterwards!
6. remember, the centre vents always blow cold air; a brilliant idea from Saab so the driver (and passenger) can get fresh air in the face and stay awake while the rest of the driver, passenger and car is toasty!
7. see http://townsendimports.com/Web/cooling_system_folder/thermostatreplacement.htm for flushing and stat replacement info
   

water pump

My 2005 Nissan Sentra 1.8s with 55,000 mi. blows cold air from the heater. Coolant not circulating in engine. Lower hose stays cool to touch. Both heater hoses cold. Changed thermostat - didn't fix it. Coolant not leaking or dirty. None in oil - no oil in radiator. Changed worn water pump belt - pump spins freely with no noise or resistance. Cooling fans come on after warm-up. Temperature gauge stays in normal range then jumps to hot and back again. Coolant good to 10 below - didn't freeze here yet. No other problems or repairs to car. Afraid to drive and make worse. Help!