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Hello all,

Fix one, thing and another thing breaks. Love it.

I am starting to get random overheating issues over the last couple months. In Nov I replaced the Thermostat, and that seemed to do it. Then 3 weeks ago, it started again so I went ahead and replaced the water pump. (only bought the car in Sept. So these are things I'd normally do anyways.)

So again, problem went away for 2 weeks. Last week the problem came back. The positive thing is an error code came with it. I Pulled the codes this weekend and I am getting a "P0125 - Insufficient Coolant Temperature for Closed Loop Fuel Control".

Fan is running. Only overheats in traffic. Once I am moving, temp goes down. I did notice today when I put my hand between the block and the fan, there was no real heat coming through.

Anyone have any thoughts? Bad Part Maybe?

2001 Firebird 3.8 V6
 

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Are you sure your car is overheating. The code is saying the coolant temp is too low. The gauge sender and the sender for pcm are 2 different senders on other 4th gens. So I will assume that 3.8 uses the 2 sender system. I'd check and see if your senders are working correctly.

A scan tool that does running sensor scans will show you the coolant temp pcm is seeing. Also we have the 2000 service manual in the 4th gen tech section. Download it and use it to test the sensors out of the car. You put them in water and heat the water until it boils. Using a multi meter set to ohms, see if the resistance readings match those listed in manual.

Having a coolant temp sensor that serves pcm be off in it's readings can serious affect your air/fuel ratio. In bad enough cases car won't run.
 

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Discussion Starter · #3 ·
Are you sure your car is overheating. The code is saying the coolant temp is too low. The gauge sender and the sender for pcm are 2 different senders on other 4th gens. So I will assume that 3.8 uses the 2 sender system. I'd check and see if your senders are working correctly.

A scan tool that does running sensor scans will show you the coolant temp pcm is seeing. Also we have the 2000 service manual in the 4th gen tech section. Download it and use it to test the sensors out of the car. You put them in water and heat the water until it boils. Using a multi meter set to ohms, see if the resistance readings match those listed in manual.

Having a coolant temp sensor that serves pcm be off in it's readings can serious affect your air/fuel ratio. In bad enough cases car won't run.
I guess anything is possible. The Temperature gauge runs normal. Randomly when I hit a stop light, it jumps to the Red Zone.
 

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Ramblin' Wreck
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The code is telling you the coolant temp did not rise to at least 140 F within the first 7 minutes after a start with the temp already above 50 F. Was this a cold start with the air temp above 50 F when this happened? Since these gauges are not very accurate, I would get a code reader that shows real time data to see what the sensor says and watch it for the first 7 minutes.

http://www.amazon.com/RioRand-RS310-OBDII-EOBD-Reader/dp/B005KOZ25Y/ref=pd_sim_sbs_263_1?ie=UTF8&dpID=41e58j3zm%2BL&dpSrc=sims&preST=_AC_UL160_SR116%2C160_&refRID=02V3WPTYEM2HEK3C7RXH
 

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Discussion Starter · #5 ·
Temperature here in Florida this morning is a beautiful rainy 65 F. I have a Actron CP9680, which I used this morning to run live data. Car got up to 192f within the first 7 minutes and stayed their the whole 25 minute drive to work. Once I got to my Workplace and had to sit in the parking traffic, keep an eye on the data stream. I rose to 222F when I turned on the heater. Temp dropped back down to 208F, when I turned the heater off, and the temp continued to drop to 196F. After a few moments, it started to rise again reaching 223F, before slowly going back down to 206F. It did this 3 times of the next 12 minutes.

Again, the thermostat is only 2 months old, but still could be sticking. I only purchased the car in Sept, with 120,000 miles. Probably could use a Radiator/Coolant flush maybe, thoughts?
 

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223 degrees is not over heating. In fact that is about the temp that pcm commands fans to turn on. Redline is like 260 to 270 degrees.

I find it strange that temp got higher when you turned heat on. Heater core is like a small radiator and when heat is on, it should cool the water temp at least a couple of degrees. Maybe heater core is plugged up.

A temp reading that swings from hotter to colder on a frequent basis, can be one of the indications of a head gasket getting ready to let go. So check to see if the fans coming on is why temp goes back down.
 

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1994 Firebird Formula 381ci LT1 / TH400+GV O/D
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I think he meant to say "it rose to 222F (and then) when I turned on the heater, temp dropped back down to 208F".

The engine was designed to run at the mid-point of the gauge, ~210degF. If it has dual fans, low speed is programmed to come on at 226degF (or if A/C is on, including defrost setting), and high speed at 235degF. It isn't overheating.

Probably wouldn't hurt to check the radiator for blocked air flow (leaves, plastic bag, debris, heavy dust accumulation). When was the last time the coolant was changed and the system flushed? That's all part of normal preventative maintenance.
 

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Discussion Starter · #8 ·
I think he meant to say "it rose to 222F (and then) when I turned on the heater, temp dropped back down to 208F".

The engine was designed to run at the mid-point of the gauge, ~210degF. If it has dual fans, low speed is programmed to come on at 226degF (or if A/C is on, including defrost setting), and high speed at 235degF. It isn't overheating.

Probably wouldn't hurt to check the radiator for blocked air flow (leaves, plastic bag, debris, heavy dust accumulation). When was the last time the coolant was changed and the system flushed? That's all part of normal preventative maintenance.
You are correct, I should have typed "it rose to 222F " more clearly.

As Mentioned, only have had car a few months, so No idea about the system ever being flushed. Soccer Season just ended, so i now have the time to get everything done and fixed on the car.

Yesterday, the Temp Gauge Did Redline, which is my I started this thread.
 

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1994 Firebird Formula 381ci LT1 / TH400+GV O/D
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OK..... in the red. But the conditions you described in post #5 did not indicate that was happening.

Since you know little if anything about the condition of the coolant, I would start with a flush and replacement. I would think that would have been done as part of the water pump and thermostat replacements, so maybe I missed that part too. Checking the air path through the radiator would seem to make sense. What temperature t'stat did you install?

It's very common for the heater core coolant loop to plug up, but yours does not appear to have that problem since running the heater did help cool the system.

To clarify (and maybe to learn??) I think there is only one coolant temp sensor on the later year 3.8L V6's. The 2000 shop manual diagrams show that the single sensor feeds the PCM, and the PCM then passes that info, along with RPM and fuel level to the solid state logic module in the instrument cluster, which then feed the tach, CLT gauge and fuel level gauges.

Can your scanner indicate the status of the fan relays? You are looking to see if Relay 1 for low speed operation is powered and Relay 2/3 for high speed is powered at the appropriate temperatures.
 
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