Inherited moms car (2003 Malibu) when she passed few months back, no idea when she had fluids checked last etc... temp gauge has been slighty erratic..nothing to extreme but fluctuating between tick under half and tick over half- when idling in traffic sometimes 2/3 but never overheating also heat would come and go..usually once gauge reaches slightly above 1/2, heat would kick in and make gauge lower..itd run for a few n then go cold until gauge climbs again...rinse and repeat.. yesterday afternoon gauge was workin same as described left this morning for work, guage never left initial starting point on 15 min drive..no heat either same on drive home checked coolant, reserve tank was almost dry..refilled drove around block to see if it changed...got heater to work whole drive but still no movement on gauge have been told possibly thermostat issue?
If the thermostat is bad (i.e. stuck open at all times), this would allow coolant to circulate in the engine even when it is below the desired operating temperature. This leads to OVERcooling of the engine. You can either replace the thermostat as a first step or remove it and test it -- closed when cold, open when heated above 190-200F.
SOURCE: Engine overheating in traffic or when idling
I'm assuming your car has the Northstar engine?.
Strangely enough,if you remove the thermostat in the Northstar engine, it will overheat, this is because the stat is both a thermostat and a pressure valve.I can't be bothered to explain in detail how the whole cooling system works but please understand that you need to put the stat back in,(or preferably a new one).As for the cooling fans,what you described is normal for the Northstar.
Further to this, look at my profile,I have provided similar solutions for overheating problems.
SOURCE: 2003 Protege 5 overheating on long runs.
I just replaced the radiator and thermostat on my 03. The radiator was defective (corroded) on the lip where the cap seals. This allowed coolant to be spat out. The thermostat was also sticking closed after new radiator and this caused overheating. Replace both while in there for under $100 if doing it yourself.
SOURCE: 2002 malibu runs hot.
Sounds like you have a faulty head gasket or maybe a cracked head.This can cause overheating and the check engine light to come on.The code for the o2 sensor is probably caused by coolant getting into the exhaust system and coating the sensor.The coolant fan may work but it cannot remove enough heat from the rad to make the engine cool off.Try some engine coolant stop leak to see if it will help.This maybe only a temperary fix.Let me know if you need more.MOE
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