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Overheating prob

Tiny
KENNY1984
  • MEMBER
  • 1994 OLDSMOBILE CUTLASS
  • 6 CYL
  • 2WD
  • AUTOMATIC
  • 135,000 MILES
Cooling fans work but do not turn on when needed tried to unplug the ect sensor and still nothing. If I ground the relay after the pcm it comes on
Tuesday, December 28th, 2010 AT 7:21 PM

11 Replies

Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,867 POSTS
Have you tried replacing the relay?
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Sunday, January 2nd, 2011 AT 11:09 PM
Tiny
KENNY1984
  • MEMBER
  • 7 POSTS
Yes I have replaced the relays, radiator, therm, all three coolant sensors, and also tried running the fans off a switch and the car still keeps heating up. Therm works in boiling water and I have heat. Had it in the shop they had everything working but the gauge went half way up the gage then fan kicked on then went to normal operating temp. Hour after I left the shop it started doing the same thing.
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Monday, January 3rd, 2011 AT 2:52 AM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,867 POSTS
I need to confirm something. When the vehicle is driven at highway speeds, does it ever overheat? Also, have you double checked grounds?
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Monday, January 3rd, 2011 AT 12:36 PM
Tiny
KENNY1984
  • MEMBER
  • 7 POSTS
Yes it runs almost in the red zone while driving I ran fans off battery no good. I tried compression and block test compression test neg I got about 160 psi on all cylinders or is that not right it has a 9:1 ratio. I drilled a hole in the thermostat and it runs cooler for a while but starts to heat up over about a half hour drive
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Monday, January 3rd, 2011 AT 3:11 PM
Tiny
KENNY1984
  • MEMBER
  • 7 POSTS
Which ground? I belive its an internal ground on the pcm there is a green wire that goes to the relay but I followed it back to a plug going into another wire harness that looks like it goes to the firewall there is contunuity so no break in that wire. Does the temp gage itself have anything to do with the ground
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Monday, January 3rd, 2011 AT 3:18 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
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No to the temp gauge. I have to say, if it overheats while driving at highway speeds, chances are the fans are not going to fix it. There has to be either an air block, coolant blockage, or a bad head gasket.
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Monday, January 3rd, 2011 AT 4:16 PM
Tiny
KENNY1984
  • MEMBER
  • 7 POSTS
Wouldnt me putting a small hole in the thermostat prevent an air lock though?
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Monday, January 3rd, 2011 AT 5:02 PM
Tiny
KENNY1984
  • MEMBER
  • 7 POSTS
Im working on this now the wires to the sensor and from it bact to pcm are good. Ground in pcm also looks good. I just noticed that the metal heater hose that comes back to meet with the lower radiator hose is a triangle shpe not round like it should be. Fixing that now. Can a bad head or head gasket make it so the fan will not work right since that ect sensor is right in the manifold. And in turn could that hose be my problem
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Monday, January 3rd, 2011 AT 5:54 PM
Tiny
JACOBANDNICKOLAS
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Yes, it is possible.
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Monday, January 3rd, 2011 AT 6:12 PM
Tiny
KENNY1984
  • MEMBER
  • 7 POSTS
Final thought and I appreciate the help. I fixed that hose and ran a pressure test all good no leak down on the gage which means no leaks and block test is neg fluid is still blue. I backflushed the system when I draind it to fix the heater hose. No leaks on pressure test and block test is neg can I still have a head gasket or head prob. The fans still arent working when temp is at normal. I checked with thermomiter after I bled the system I few times. Im ready to just use the hammer on it this way I know why it dont work lol
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Tuesday, January 4th, 2011 AT 2:37 AM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
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It could still be; however, I would think you would have picked up on it by now. Kenny, based on everything you have done, something is telling me the PCM isn't sending a signal to turn the fans on when the correct temp is reached. Either that or you have a bad wire at some point, but if I recall, you have gone through all of that already. You may need to have the PCM checked to see if it is doing its job. Honestly, there isn't anything left.
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Tuesday, January 4th, 2011 AT 1:09 PM

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