James1974 Posted August 14, 2008 Report Share Posted August 14, 2008 On my 11/99 production Northstar in an STS...I am boiling over. I checked for a bad head gasket...carbon tests...plug conditions, compression tests. All tests OK. I flushed, changed thermostat, the water pump and belt, added tablets, purged air via the little purge hose. I Teed into the system and forced hot water throughout to no avail. Through this- I pulled all hoses I could locate and made sure to get all air out. I pulled hoses and checked for good flow through the radiator- then noticed the fans were not kicking on. I removed the two relay covers and pinned them closed. The car seems to be very happy as long as I run the fans manually. What sensor(s) control the fans...where are they located on the car- and where might I buy them. Autozone does not show them in their "system" and offered a generic "kit" to wire them yourself and stick a temp probe into the raditor fins. What a joke! I feel the temp sensor is out of spec- as the one fan has kicked on- but much later than it needs to prevent overheating and boilover. Keep in mind I am very much onto air pockets and cavitation- and I am certain this is not happening to me. My AC system had got a stone into the condenser or other leak and is inoperational. Does the fan that kicks on with AC operation kick on in other scenarios...(high temp...normally...camel mode, etc.). Do the fans get turned on in series for a "low" operational status? Is this true? What triggers the fans...one sensor...two sensors...where on the car do I find it? Who sells it? Dealer only? What is it called? Do I need to think about a "brain" or CPU being bad...I have seen one fan kick on at least during overheating conditions. Can anyone help with these questions or add any insight here? Link to comment Share on other sites More sharing options...
jking220 Posted August 14, 2008 Report Share Posted August 14, 2008 Im sure others who know better will chime in, but I do know that just one fan comes on at first, then once the temp gets even higher, the second fan comes on. If you have your ac on it runs both fans all the time. Im sure you can replace the sensors with OEM and not have to do a "kit" from autozone. Thats a joke. I found an "fan relay switch" on gmpartsdirect.com for your car. It shows it is 18 at the dealer and 10 online. I dont know where it is or if there are more than one of them, but this might be your cheap solution. Sorry if this is a stupid question, but are you running 50/50 in your coolant? You said something about forcing hot water through the system, and if you are running straight water you will boil at a lower temp than 50/50. Have you run your codes? What are your overheating signs? Jonah Link to comment Share on other sites More sharing options...
JimD Posted August 14, 2008 Report Share Posted August 14, 2008 Does the fan that kicks on with AC operation kick on in other scenarios...(high temp...normally...camel mode, etc.). Do the fans get turned on in series for a "low" operational status? Is this true? A/C operation has the fans on 100% of the time for air flow over the condenser. Otherwise, the PCM controls the fan relays to connect the fans in series when the coolant temperature reaches approximately 223 degress F. If the coolant temperature continues to rise, the fans will be switched to parallel operation at approximately 234 degrees F. A coolant temperature sensor is buried in the crossover if I am remembering correctly If you have only one fan running, you could have a defective fan motor or loose connector at the fan that is not operating. That would certainly prevent the series operation intended at 223 degrees. Jim Drive your car. Use your cell phone. CHOOSE ONE ! Link to comment Share on other sites More sharing options...
Cadillac Jim Posted August 14, 2008 Report Share Posted August 14, 2008 The fans run at the same speed. If one of them is on, the other one is stuck. Make sure that nothing is holding the blades and that both turn freely. If the sticking is in the motor, replace the fan. The Northstar, like most engines designed since, is a reverse-flow coolant design. Make sure that the thermostat isn't put in backwards. The thermal sensing side should be inside the water pump housing. Make sure that the coolant is 50/50 antitfreeze and that the radiator cap is OEM 15 pounds. The radiator cap on the Cadillac vents differently from overflow tank radiator caps. -- Click Here for CaddyInfo page on "How To" Read Your OBD Codes-- Click Here for my personal page to download my OBD code list as an Excel file, plus other Cadillac data -- See my CaddyInfo car blogs: 2011 CTS-V, 1997 ETC Yes, I was Jims_97_ETC before I changed cars. Link to comment Share on other sites More sharing options...
Ranger Posted August 14, 2008 Report Share Posted August 14, 2008 If I remember correctly the ECT (Engine Coolant Temperature) sensor is on the rear (drivers side) of the right bank (rear) head. Near the EGR valve & master cylinder if that makes it easier. Link to comment Share on other sites More sharing options...
Logan Posted August 15, 2008 Report Share Posted August 15, 2008 The PCM should command the fans on when needed. That being said, 10-15 years ago I had a 4 cylinder Buick Turbo that would run hot. The real fix was a aftermarket thermo fan relay kit. It had a temperture sensor you could force into the radiator 'vanes'. Then had a adjustable temperture relay. It fixed the car. The Opel 4 turbo's were known for running hot. How I wired it in. I forget. Been 10-15 years.. Logan Diagnostic LLC www.airbagcrash.com www.ledfix.com www.ledfix.com/yukontaillightrepair.html www.ledfix.com/ledreplacements.html www.ledfix.com/j42385toolrental.html Link to comment Share on other sites More sharing options...
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