Throttletune or any other mechanics My sons 93 Cavalier overheated the other day. Anyway the electric fan is not turning on (runs normal temp as long as your moving) so I checked the relay, its working. It is sending 12-volts to the fan, the other wire is a good ground. I wanna know if I need anything special to change just the motor. How do I remove the fan and reinstall it on the new motor. Throttletune, you've heard this before, the fan had always turned on with the AC (not any more) but not with engine heat. I'm also gonna replace the coolant temp sensor and thermostat (I just think it a good idea to replace it after an overheat). The green/white wire going to the computer does go low (to ground) and turn on the relay. I've already cheched that. So now we need to figure out how to make it turn on with temp. The temp sensor has two wires, a black and yellow, both go to the computer, so one has a reference voltage on it the other varies. I'm gonna assume that the black is the reference voltage wire because it goes to 5 other sensors (including the TPS, air inlet temp sensor and MAP sensor.) So can you tell me the voltage that is necessary on the yellow wire so that the computer tells the fan to turn on?
I dont really have any advice, but this must be a popular problem. The same thing happened to my sisters car, it overheated and blew a head gasket. Her car is a '95 though. I think the problem turned out to be the thermostat.
As far as I can tell there is no damage to the car, in fact I drove it 22 miles to get it home. I just picked a route so that I would only have to stop once. I drove home with the AC on( it was 91-degrees out) and temp stayed normal, except for that one stop light. But as soon as I started moving again temp went right back to normal. I even drove it to church this morning. We just can not do any city driving without the fan. I'll work on it next week end. I just need to know what the voltage should be on the yellow wire so that the computer turns on the fan
Wish i could help on that........ Not tryin to jump off the topic here, I run an old dodge duster for years with no fan, Was fine as long as you were moving , even in town did ok.... But that is old tech stuff with more thermal mass than the newer cars ........which dont like alot of excessive heat!
You know how many red necks told me "just throw a switch on it". I may not be a mechanic but I do understand the electronics and how it works. I can actually figure it out for myself, but if some one has the info it would save me some time. Look what I learn today. I understand most of the cooling circuit, the reference voltage on the coolant temp sensor is 5 volts. Measured it a couple of hours ago. And it is the black wire. I had a 71 Plymouth Duster, sold it when I went back to school. It had a 360, Holley Pro-Jection Fuel injection System, MSD 6A ignition with a Mopar Performance Recurved Distributor. Crane Cam, 88 360 Fast Burn heads Slightly reworked. I loved that car. It was a real street car. Smooth idle cam and 9.8:1 compression. It would run 14.0 @99mph in the quarter mile. It was a strong performer. Even had working AC, but this is Texas and AC is a Must
but, the rednecks are right, you cant ifgure it out an other way.......put a switch on it!!!!!! Better than NOTHING if you dont have the means to diagnose and toubleshoot the problem... But, I agree, any problem worth lookin into is worth fixin....
When you turn on the a/c you should get a set voltage going from the a/c to the relay which should close it which should start the fan. I know the temp sensor will send more voltage as the engine temp increases until it reaches a set voltage at which point it should start the fan. That set voltage should be the same from both circuits. Just check the voltage coming off the a/c circuit and you sould get that magic number which start your fan. I hope this helps you in someway.
Hi Ranger, The fan on that is scheduled to turn on at 223 degrees. If you have power and ground to the fan, and no operation, then I would just go with the fan on that. T-stat never hurts as far the reason you gave. I would have to assume the sensor is good since it appears to be doing what it is designed to do. Best way to verify is to look at IAT, and ECT first off before starting the car in the AM. Make sure they agree. Then, watch scan data, and look for fan request at 223 degrees. When in doubt, tag the yellow wire and it should have a steady high voltage and then as the car warms, it should slowly drop to "around" a volt or so. The black wire is the sensor ground. Resistance at 210 degrees is 185 ohms, 70 is 3400 ohms, and 40 degrees is 7500 ohms. This runs through a dropping resistor in the PCM, so the hotter she gets, the lower the voltage. As far as swapping the fan, it should be a walk in the park. Try for a Delco to make you life easier, if you can. Fits better. As far as removal, a plug in, 2 bolts on top and one on the bottom, or a slide in at the bottom possibly. Meaning, you remove the whole assy, then do the motor off car.
so your saying the lower resistence equals lower voltage. I always thought is was the other way around, higher engine temp would give more voltage. Doesnt the pcm use this voltage to power the fans, or does this fan have a seperate power supply from somewhere else. I alway thought that once the voltage got to around 11 volts it would close the relays and spin the fans and once the temp dropped the voltage would drop and then open the relay at a certain point and the fans would stop. Am i just being to simple. Im always willing to learn new things esp how lower resistence equals lower voltage. Please explain this in more detail please.
dang throttle, that was pretty good explaining man but i would put a switch in it and it works just as good and you gotta watch the temp gauge to know when to turn it on but in my mustang i always turn it on as soon as i start the car because those two 80mm turbos get hot fast and glow white so the car exceeds reg. temps especially when i racing, i remember when i was adjusting the fuel regulator after a race,i leaned over and my elbow hit that bad boy, OMFG next thing i knew i was on the groung crying like a little girl rolling around in pain,and finally the paramedics came over,it seemed like it took them forever but everyone said they where there in a heartbeat,but i dont know that burn must have slowed down my adreneline or sumthin...OH by the way throttle the 351 came out of that stang and i got the 460 hot tanked,bored 40 over and painted and ready for a new life...
Thats exactly what I need to know, thank you very much. I love electronics, I could almost be a mechanic
Hi fstrfvo, You are not imagining things. I'm at work and have a total crapload of junkers, and I mean junkers, to look at so I am going to be sort of brief here. "Most" car ECM's use a 5 volt reference voltage out of it. For the sake of a quick arguement, lets say you go to the signal wire on a TPS. You have a 5 volt reference to the sensor, you have a sensor ground, and then you have the signal wire. The TPS is a potentiometer which has more resistance if the car is at idle, and less as the throttle is depressed. So, the wiper across the resistor is the "signal return" wire, and as it hits lower resistance, the voltage increases. That is your thinking, and it is entirely correct. In simple terms. Now, on the ECT circuit, that crap changes. Inside the ECM, there is a dropping resistor, and the Engine Coolant Temp sensor is also a resistor. You have 5 volts out of the ECM, which was the yellow wire, and you have ground, which is 0 volts. You measure voltage between 2 resistors, and you are basically measuring voltage drop. Simply put, the resistance goes lower in the ECT, the current changes, the circuit is "using" more voltage, and because of the resistor in the ECM, it sees less voltage which equates to higher temerature in that circuit. So, the processor takes that voltage that should equate to 223 degrees, and it grounds a relay in the cooling fan circuit. All it is doing is completing that circuit on the control side of the relay, and allowing the higher amp side of the relay to run the cooling fan. Yep Dreamz, a switch would be all good for something like what you drive. But, we are talking a commuter car, and with traffic, and just plain driving, maybe a switch may be lost in the shuffle? Just my thinking there. Glad to help, Ranger.
props to throttle for the detailed explanation i dont think i can write something that detailed you know you can write a chilton's manual with that kinda detail lol
Thanks Dreamz. Notice, it was 'splained as "something you drive" as I had a feeling that nothing you owned was as built from the factory. And, more power to ya!
