C5 1997 overheating help.please
Thread Starter
Heel & Toe
Joined: Sep 2006
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C5 1997 overheating help.please
I am new. please help!!! My engine is overheating. My waterpump went out, this I changed, but it is still overheating. I checked the thermostat. This was not the problem. My fans are not coming on. I hooked them directly up to the battery to see if they work, and they do. I am sure it is a sensor, but I do not know where to look for the sensor. I have checked the fuses and the relays,all are working. Please help, I miss driving my car. I cannot drive even a third of a mile before overheating.
Team Owner
Joined: Mar 1999
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From: At the beach in little Rhody
Does your display indicate the correct temperature? Did you check the relay or is that how you verified their operation? Also, have you checked for debris in front of the radiator and consenser?
Melting Slicks
Joined: Jun 2004
Posts: 3,351
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From: panama city beach florida USA
St. Jude Donor '09
how do you KNOW the stat is good? ya may have air in system .any codes ? did ya knock a sensor wire off? the fans worked before?will it over heat just idling? pull off a heater hose then start car ya should have a good flow
Team Owner
Joined: May 2001
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From: Dear Karma, I have a list of people you missed.
St. Jude Donor '08-'09-'10-'11-'12-'13-'14-'15-'16
Also, let's not forget: "overheating" to a new C5 owner might mean he's seing temps in the 215-225 and comparing that to whatever he owned before.
Give a little more info.
Give a little more info.
Thread Starter
Heel & Toe
Joined: Sep 2006
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I took the stat out to see if it would still overheat. It did!! I checked all the relays with a meter. Yes, the fans worked before. Now they are not coming on. The normal temp was around 220. She almost redlined. I had to pull over and turn it off to cool down.
Burning Brakes
Joined: Sep 2001
Posts: 1,173
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From: Aguila AZ
Anytime you drain the coolant you need to fill the engine, not just the radiator bottle. Do this by removing the top radiator hose and back fill the engine through that hose. Also, if the small crossover coolant vent is blocked this will contribute to overheating. A blocked coolant vent causes an airlock that prevents the engine from filling... Check it before you back fill the engine... Once you do this you will have no more overheating problem.
If there is no coolant in the engine, the thermostat will not feel any heat and will not open causing your problem.
Shirl Dickey
If there is no coolant in the engine, the thermostat will not feel any heat and will not open causing your problem.
Shirl Dickey
Le Mans Master
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From: Slave to the evil empire
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St. Jude Donor '04
Originally Posted by harrell3us
I took the stat out to see if it would still overheat. It did!! I checked all the relays with a meter. Yes, the fans worked before. Now they are not coming on. The normal temp was around 220. She almost redlined. I had to pull over and turn it off to cool down.
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Team Owner
Joined: Mar 1999
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From: At the beach in little Rhody
If the fans run by direct power, but not by command you need to check the relays for the fans. Make sure the connections are not gunked up either. It sounds like either the fans are getting power or are not getting the command to go on from the PCM, which may think the temp is OK (getting the wrong signal from the sensor). You may also want to check the ground, according to my manual (2002) the ground is G102. I think Bill Curlee's electrical sticky has the ground locations and how to clean them.
Do you have the 97 service manual?
Do you have the 97 service manual?
Last edited by vettenuts; Sep 9, 2006 at 10:07 AM.
Thread Starter
Heel & Toe
Joined: Sep 2006
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Thanks, for the suggestions.
Yes, I have the manual. But where is the sensor? I found the one for the low coolant level but not for the fans. I am assuming with the fans not coming on, this is what is causing the overheating problem.
Yes, I have the manual. But where is the sensor? I found the one for the low coolant level but not for the fans. I am assuming with the fans not coming on, this is what is causing the overheating problem.
Team Owner
Joined: Mar 1999
Posts: 22,025
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From: At the beach in little Rhody
I know there is one coolant sensor near the number 1 spark plug, not sure if this is the one that the PCM uses or if there is a second. On my C4 there were two, one for the dash display and one for the computer.
However, if your temp display is working then the sensor should be OK. I would also set a code. Have you pulled the coolant recovery tank cap while the motor is running and made sure there is coolant circulating? How many miles on the car, water pump might be a suspect too. Also, keep an eye on the digital temp, what is it reading? The fans won't come on until 228 degrees.
However, if your temp display is working then the sensor should be OK. I would also set a code. Have you pulled the coolant recovery tank cap while the motor is running and made sure there is coolant circulating? How many miles on the car, water pump might be a suspect too. Also, keep an eye on the digital temp, what is it reading? The fans won't come on until 228 degrees.
Last edited by vettenuts; Sep 9, 2006 at 10:16 AM.
Team Owner
Joined: Mar 1999
Posts: 22,025
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From: At the beach in little Rhody
I have not checked my C5, but on my C4 the needle would be right on the edge of the red but the temp would be OK. Found this out scanning it. First time I drove it, I pulled over in total panic mode 
Melting Slicks
Joined: Mar 2005
Posts: 2,252
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From: NE OH
The temp sensor is located on the D-side of the engine, near the #1 cylinder, as someone ealier stated. You can check for coolant flow by grabbing the upper radiator hose when the car is registering hot. If the hose is cold then you have air in the system or a flow issue. When checking the fans, turn your AC on. This forces the second fan to come on earlier than it normally would.
Worst case, when the water pump went out earlier you blew a head gasket and that's causing the overheating issue.
Worst case, when the water pump went out earlier you blew a head gasket and that's causing the overheating issue.
Drifting
Joined: May 2000
Posts: 1,917
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From: Southern NH
This is what I'm reading:
- Engine Coolant Sensor is working fine since your dash gauge is showing temp and is approaching redline.
- Fans are not coming on even though the temp is rising. That indicates a problem with the fans, not the sensor.
- Does the temps stay near normal during normal highway driving? The airflow through the radiator at highway speed keeps the engine temp below 200F.
Check fuses # 49, 46 and 14 in the underhood fuse block. Check relays 45, 43 and 44 in underhood fuse block.
Also, if there's air in the coolant system that can result in a bubble at the water pump and prevent proper circulation. You need to follow the procedures in the service manual to prevent this.
- Engine Coolant Sensor is working fine since your dash gauge is showing temp and is approaching redline.
- Fans are not coming on even though the temp is rising. That indicates a problem with the fans, not the sensor.
- Does the temps stay near normal during normal highway driving? The airflow through the radiator at highway speed keeps the engine temp below 200F.
Check fuses # 49, 46 and 14 in the underhood fuse block. Check relays 45, 43 and 44 in underhood fuse block.
Also, if there's air in the coolant system that can result in a bubble at the water pump and prevent proper circulation. You need to follow the procedures in the service manual to prevent this.
Racer
Joined: Sep 2006
Posts: 260
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From: Chesterfield MI
I disagree that the problem is electrical. I think he has air in the system and therefore there is no fluid triggering the cooling fans on. I have had this problem in the past on other cars. He has to fill both sides of the thermostat and then bleed the air out. Then all will be fine!
Ray
Ray
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From: Slave to the evil empire
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St. Jude Donor '04
Originally Posted by JC in XTC5
- Engine Coolant Sensor is working fine since your dash gauge is showing temp and is approaching redline.
Drifting
Joined: May 2000
Posts: 1,917
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From: Southern NH
Originally Posted by FFR-Z06
Just to let you know, the temp reading displayed on your IPC comes from the PCM and not directly from the temp sensor.
Not that I need to explain further, but the PCM sends a 5V reference voltage to the ECT sensor on the driver's side of the block. The ECT sensor is a thermistor that varies impedance with temperature so the voltage drop across it is then read by the PCM and the temp value is calculated.
Even if the ECT was erroneous, The PCM uses that sensor input to determine when to turn the fans on. So... if the IPC is showing an overheated ECT and the fans are not coming on, then the circuit from the PCM to the fans needs to be checked out since the PCM should be grounding the fan relay to turn the fans on.
If the fuses and relays check out, then the PCM output needs to be checked.
Drifting
Joined: May 2000
Posts: 1,917
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From: Southern NH
Originally Posted by ISeeRed
I disagree that the problem is electrical. I think he has air in the system and therefore there is no fluid triggering the cooling fans on. I have had this problem in the past on other cars. He has to fill both sides of the thermostat and then bleed the air out. Then all will be fine!
Ray
Ray
There may be 2 problems here, but that's why my last question was what the temp is during normal highway driving. If it's normal meaning the airflow through the rad is keeping it cool, then there's no circulation problem, but the fans not coming on is a problem regardless.
Also, one other way to check the fan operation is to turn the AC on - that should also force the fans to come on.
Pro
Joined: Oct 2000
Posts: 545
Likes: 1
From: Charlotte NC
This may be a little obvious, but have you checked to make sure your radiator is clean? 
If you are running a stock C5 unit, they will clog easily. Straw, paper, debris, etc. This happened to me about a year ago. Oil temp went to 225 and water was 20 degrees higher also. Took radiator out and was unbelievable how much crap was stuck in the cooling fins. After cleaning temp returned to normal range.
If you are running a stock C5 unit, they will clog easily. Straw, paper, debris, etc. This happened to me about a year ago. Oil temp went to 225 and water was 20 degrees higher also. Took radiator out and was unbelievable how much crap was stuck in the cooling fins. After cleaning temp returned to normal range.