Why would the cooling fan turn on if the engine is cold?


Asked by Sep 10, 2015 at 07:43 PM about the 2002 Oldsmobile Silhouette 4 Dr Premiere Passenger Van Extended

Question type: Maintenance & Repair

I had an overheating problem which appears I solved by bleeding the
system a few weeks ago.  The cooling fans turn on when temp is reaches
107C and turn off at about 95C.  2 days ago, I found the larger cooling fan
running after the vehicle had been sitting in the driveway for 3+ hours.  I
turned the ignition on and off a few times and the fan stopped, however
about 4:30am the following morning, I found the fan running again

9 Answers


sticky relay? tap the relay to get it unstuck ? swap the effective relay with a less important circuit. If it goes away ? it was the sticking relay. See if there are related codes in memory and clear them. then monitor for several drive cycles or have it function tested comparing to normal operation in the book. 107 deg C is 224 deg F 95 C is 203 deg F Water vaporizes at 212 deg F sea level. A pressure cap applies pounds. The point of vaporization is raised 3.25 deg F per pound. Driving makes airflow. Sitting requires cooling fan operation. Some have speeds. Preset switches can be compared to spec. Auto computer can control ground. it can set codes to help or give a pass code. Thermostat opening is likely 195 deg F. A/c fan can run in several modes or continuous. Mr good wrench knows all this and can performance test, measuring actual for yours with the conditions. Relays are cheap at the u-pull-it -yard

Best Answer

After the external controls are checked, suspecting cooling system issues with a 13 year old GM car is not abnormal. flushing is bi-yearly. having your radiator cleaned out would not be over diagnosing. See what your tests reveal now. preventative servicing may be a good idea, but those numbers are not really depicting trouble. compare ambient, and what it does accellerating up a long grade. Then look at any temp indicator and read ECT. that's what Mr. G may do for you.


If you suspected combustion leakage you can get a vapor reading fluid tester to use at the parts store. you just hold it over the open system with the test fluid added to the tester. look for it to discolor. Ask at a reputable part store where experienced countermen can assist, unless you get it done after a tech deems it worth checking.


Thanks for the responses - I may not have been clear in my original description, but it just happened again. The van has been sitting in the driveway, for about 4 hours, the engine is ice cold and the fan just kicked on for no reason without even pulling it out of the driveway or the key even in the ignition. I'll check/swap fan relays but still don't understand how a fan would kick in on a cold engine. Normally the fan(s) don't work when you need them, not when you don't.


The sender or switch designed to tell the coolant temp must be in range. if it tested out of range, it would produce unnecessary operation. The relay can be affected by underhood temp and years of exposure to. a malfunction is a strange thing so must seem correctly run tests. They require connection to the affected circuit(s) and monitoring. Where does the command come from to operate it and why? That's what you want to know, and shotgunning parts at the problem can make it confuse and elude you. But not Mr. G, hopefully. He may understand the description, need to have it act up ? or may try the most likely part and swap in a good one. After 10 years the plastic and the saved weight leads to parts that malfunction accordingly. See what he says or research it yourself through the public library. Guesses get expensive so I would ask the guys with regular experience. My experience is people who want super magic, instantaneous answers. The swapping in for process of elimination as an educated guess has been the luck. Real tests prove what and why. Sorry this is a long read, but howto cram 20 years into a paragraph ? Try, try as you might? you may need the pros.


reading threads full of guesses does not always help and they do not return with their actual findings. Computer databases for automotive cost money, but they have actual data. Your library keeps access using tax money and you provide the time, the vehicle info, and the desire to have an answer. Or you hire it done, either way. the research tells you what guess to make and educated technicians run tests, service codes or monitor live data stream. You could find the info source for fan needed, The parameters for the command, and the driver for the function. then the relay gets signalled to send the power like a switch, the auto computer sends the signal. When they all have no function? What signals the relay? That is the test to explore. Or ask Mr. G. that's his job.


The hours of "hot soak" affect the plastic. the temp of the coolant affects the sensor or switch. The EPROM knows the parameter. The EPROM affects the processor driver. It can set a code ? It can think it is correct. Which is it ? Measure and compare data, use a scanner tool, or try a known good "whatever".


System prechecks demand inspection of the components, their harnesses their connectors, and the surrounding conditions. what are they? I cannot measure from here. but you may try or ask at your GM garage. Ask for service bulletin data, or most likely suspect from your tech and service advisor. That's the most flawless people schematic.


Of course it is only obvious that higher ambient makes conditions. Trapping heat makes conditions, processors can be flash updated or so can auto computer parts. they must receive correct data. Resistance and connector trouble can mess with things, add-on systems and tampering cause conditions that exist on only your car. just as previous repair attempts, jumper wires, or other unforseen conditions of substandard repair attempts. What are your readings to the pinpoint tests that is my new question for you.

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