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1998 Pontiac Firebird 3.8l 5 speed manual
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Discussion Starter · #1 ·
I have a 98 stock firebird. I just replaced the radiator, heater core, thermostat, and water pump because I found stop leak in the old radiator. I believe I have blead all the air out of the system. Anyway you can direct me on this would be grateful. She will get to temp at idle. But as soon as I start driving the car she instantly drops to 170° without running the heater
 

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First, where are you reading the temperature? From the gauge or PCM? The gauge can be very wrong, you will first need to use a multimeter on the sensor to see if it is reading accurate. The PCM could also be wrong if the sensor is going out of spec., same thing, verify with a multimeter. My temp gauge reads 20F below actual now, but my coolant temp sensor is still accurate, and that's all that matters as the fans and such are controlled by the computer, not the gauge. The gauge is "for our eyes only".

I do not know anything about the v6, but I do know it's winter and the cold air will have a dramatic effect on cooling. I'm assuming you have a 160F thermostat? If so, anything between 160F and 200F would be considered normal operating temp. If you have a 180F thermostat, you would be seeing fluctuations between 170F and 180F as the thermostat closes and opens repeatedly. Is that happening?

I don't think you have a problem. Maybe just a bad sensor for the gauge.

With my V8, which has a 180F thermostat, on the hottest, muggiest of summer days, my engine runs between 191 and 197F unless I turn on the A/C, then it runs in the 220's. ...my guage reports in the 170's which is below my thermostat rating. ...not possible.

Here is a link to the 1998 specific Factory Service Manual. It will lead you in testing both sensors.

 

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Welcome to the forum.

if you had air in system, temp would be very hot. The gauges in these cars are not always right on the mark.

If you have an obd 2 scanner that does real time sensor data, see what temp PCM is seeing and compare to gauge temp.

I wrote this, this morning, and forgot to hit the post reply button.
 

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Registered
1998 Pontiac Firebird 3.8l 5 speed manual
Joined
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2 Posts
Discussion Starter · #5 ·
First, where are you reading the temperature? From the gauge or PCM? The gauge can be very wrong, you will first need to use a multimeter on the sensor to see if it is reading accurate. The PCM could also be wrong if the sensor is going out of spec., same thing, verify with a multimeter. My temp gauge reads 20F below actual now, but my coolant temp sensor is still accurate, and that's all that matters as the fans and such are controlled by the computer, not the gauge. The gauge is "for our eyes only".

I do not know anything about the v6, but I do know it's winter and the cold air will have a dramatic effect on cooling. I'm assuming you have a 160F thermostat? If so, anything between 160F and 200F would be considered normal operating temp. If you have a 180F thermostat, you would be seeing fluctuations between 170F and 180F as the thermostat closes and opens repeatedly. Is that happening?

I don't think you have a problem. Maybe just a bad sensor for the gauge.

With my V8, which has a 180F thermostat, on the hottest, muggiest of summer days, my engine runs between 191 and 197F unless I turn on the A/C, then it runs in the 220's. ...my guage reports in the 170's which is below my thermostat rating. ...not possible.

Here is a link to the 1998 specific Factory Service Manual. It will lead you in testing both sensors.

Thank you. I was indeed a bad sensor..... or two lol. But it's working correctly now.
 
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