Question about 1985 Chevrolet Monte Carlo

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Temperature gauge is inaccurate and check engine light comes on but its not over heating and everything else is fine can it be a sensor ? The temperatue gauage didn't read anything for months but now started working but reads false sometimes 260 degrees but now the check engine light comes on and off. I did change the sending unit on the head by the spark plug. Check engine light comes on and off and temperature gauge gives false readings but not over heating etc, etc . Whatelse could it be ?

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  • serf51 Oct 20, 2009

    The antifreeze level is fine and installed a new thermostat the heater blows hot air. Temp gauge might read 120, 200, 260 etc but is not over heating everything is fine but now it seems since the gauge started reading something and the gauge hits 220 the check engine light comes on the gauge will go to 260 then start going back down but like i said everything is fine. Would the oxygen sensor make the heat gauge act up ? PS checked all the wireing too.

  • serf51 Oct 20, 2009

    Its not taking any anti freeze and its a brand new radiator and the thermostat i drilled a hole in so it doesn't get air bound. Its all new coolant put in the radiator. It doesn't have a serpentine belt but all the belts are good. Its a 1985 Monte Carlo SS with a 305 engine. I will try starting the engine cold without the radiator cap and let run awhile and i'll change the oxygen sensor to see if that takes care of the check engine light. Its not taking any water or do i see leaks so like you said they usually start leaking water. Thank you so much for your help sir, i'll try what you said and go from there.

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Have you checked the antifreeze level lately? Low antifreeze will cause a temp sensor to give false readings. Does your heater work OK, as in does it blow hot air when heater is on? that is another symptom of low antifreeze.

As far as the check engine light coming off and on, I would bet it is the oxygen sensor that might need to be replaced.

Posted on Oct 20, 2009

  • Brian Anderson Oct 20, 2009

    Have you drained the coolant or put a good amount in lately? The way you describe the temp guage, it almost sounds to me like you have an air pocket in the coolant system. basically it works it's way through the system and when it gets to the water pump the pump can't get the water moving until something gets water back to the pump, and when it starts pumping again the coolant in the radiator that has cooled makes it's way past the temp sensor which is why you get the normal, hot and then cool readings. Try taking off the radiator cap when it isn't hot and then start the engine and let it flow and if there are any air bubbles they will work themselves out that way when they can't escape when the cooling system is sealed.



    If it's not that, then I am going to have to do some thinking about what else it could be. maybe the water pump is going bad....? but they usually start leaking when that is the problem. Is the serpentine belt in good shape and tension if so is there any oil or something on the belt that would cause the water pump to not turn up to required spec.?

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Coolant Temperature Sensor printpage_icon.gif



0900c152801bfc38.jpg enlarge_icon.gifenlarge_tooltip.gif

Fig. Remove the coolant temperature sensor
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0900c152801bfc39.jpg enlarge_icon.gifenlarge_tooltip.gif

Fig. Beginning with model year 1994, the Engine Coolant Temperature Sensors combined the sensors for the ECM and the gauge into one sensor-1997 2.8L V6 sensor shown


0900c152801bfc3a.jpg enlarge_icon.gifenlarge_tooltip.gif

Fig. The electrical connector for the combined temperature sensors is keyed to avoid improperly connecting the sensor's wiring-1997 2.8L V6 connector shown

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