The coolant temperature gauge in my 2000 Bonneville fluctuates from cold to hot randomly. The engine coolant temperature is not overheating but the gauge will say it is then drop to cold in seconds. I replaced the thermostat and temp sending unit with no effect.
Watch the temp gauge when the electric radiator fans come on. The temp sensor that controls when the fan comes on may be faulty.
SOURCE: 2000 Sunfire coolant problem. Engine overheating,
ok, its time for a radiator flush. there is major sludge in the internals of this radiator. Make sure the thermostat is in the correct position as well. I've seen many cars come into my shop with the thermostat inserted backwards.
SOURCE: Replaced thermostat and MAF sensor but temp still all over the place and car shakes in idol
Radiator may also be partially plugged. This usually becomes evident mostly in the spring, when ambient temps start to rise. When in motion, air flowing through unplugged radiator is sufficient to keep temp down, but at idle, fan can't pull enough air by itself. Since outside air isn't as cold, heat transfer is incomplete.
I'm sure someone out there will argue about my method, but I disconnect lower hose and block off the radiator lower connection, then do the same at the top. I use one container of CLR and pour directly into radiator (if you don't have a fill cap, use upper hose opening instead of blocking it) slowly pour in water 'till it's full. Leave for an hour then drain, use a garden hose to blow water through from top, out through bottom till it runs clear Seal off outside of hose to get pressure into radiator, wrap rag around it), then re-connect hoses, re-fill with coolant. (engine running heat full on).Generally this will give you most if not all flow restored.
SOURCE: no heat in car ,new coolant ,new thermostat
Had the same problem and turned out to be that the Heater Core was clogged. Took it to a Radiator shop and they blew the system out to unclog it. Cost was $25.00. 2005 Grand Prix.
http://howtobyme.blogspot.in/2012/05/2004-toyota-tundra-oil-gauge-and-temp.html
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http://technoanswers.blogspot.in/2012/04/toyota-4runner-temperature-gauge-sensor.html
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http://schematicsdiagram.blogspot.in/2012/04/temperature-gauge-sits-over-half-way.html
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http://technoanswers.blogspot.com/2012/01/heater-blows-intermittently-and-temp.html
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http://technoanswers.blogspot.com/2012/01/temperature-gauge-keeps-fluctuating-up.html
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http://technoanswers.blogspot.com/2012/01/temperature-gauge-on-dash-quit-working.html
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http://technoanswers.blogspot.in/2012/02/dodge-neon-gauges-not-working.html
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http://schematicsdiagram.blogspot.in/2012/02/heater-blows-cold.html
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http://schematicsdiagram.blogspot.com/2011/12/heat-blows-cold-on-drivers-side-and-hot.html
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1992 Lexus LS400: Engine overheats,
Antifreeze out of reservoir and heater Blows Cold Air?
http://whatisbyme.blogspot.in/2012/05/1992-lexus-ls400-engine-overheats.html
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These details will help.
Thanks.
This sensor monitors the temperature of the engine and sends that information to the engine control computer to regulate the amount of fuel needed - more if engine is cold and less if it's hot. The signal generated can also be sent to the temperature gauge as a visual indicator of overheating and imminent danger
This sensor monitors the temperature of the engine and sends that information to the engine control computer to regulate the amount of fuel needed. More fuel is needed if the engine is cold; less if it's hot. If the temperature is extreme, the signal will be sent to the temperature gauge as a visual indicator of overheating and imminent danger.1,131 views
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