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Discussion Starter · #1 ·
ok guys i need help again.. the fan in front of the engine isnt turning off when i turn the car off and im having to disconnect the battery.. i remember seeing someone having the same problem on here before but i cant remember what the problem is.. i thought it was some switch or something ... can anyone help? someone said the fan could stay on even after the car is turned off but i disconnected the battery for 30 mins and reconnected it and the fan still comes back on
 

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there are two sensors that turn the fan on. One while the AC is on and one while it is off. I'd guess one of those two died in the on position. Or you could have a short. Check all the wires for rubs etc. I think the sensors are pretty cheap and fairly easy to get at.
 

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Discussion Starter · #4 ·
thanks guys i think the relay was stuck or something.. all i did was disconnect the battery again.. this time take the cooling fan fuse out on drivers side and so far its fine
 

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Tim said:
thanks guys i think the relay was stuck or something.. all i did was disconnect the battery again.. this time take the cooling fan fuse out on drivers side and so far its fine
mine was doing that too. I'm sure it will probably start doing it again. I have a sensor but apparently they gave me a diffrent one than the one i needed. The one they gave me fit the sensor on the right side of the thermostat Does anyone know the name of the sensor that is beside that one to the left. Thats the one that needs replaced because it's broken. If i can find out the name then i can go to advance and replace it.
 

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I'm having the same problem. I'm not so sure it is because of a sensor because as soon as I pull the fuse it stops and does not start back up when I replace the fuse.

It's a fairly new relay, only about 2 years old so I'm surprised it's causing problems. Still, I think what is probably happening is that the contacts are welding themselves together when they first connect. (I don't know if any of you guys have played with high amperage battery packs before but even a 7.2v sub-c NiCad cell can create a good enough weld to hold wires connected where without any current flow they would fall apart.)

The new relay replaced an old one that burned up when the fan got packed with snow. Since the fuse didn't blow until the relay had melted itself to the connectors, it probably caused some serious problems with the fan brushes and commutator which is probably causing the fan to draw significantly more amperage. This theory is supported by the fact that the new relay is showing signs of overheating.

Even if none of your fans were abused as badly as mine, the brushes and commutator could be in bad shape from dust, water, or just age. And that makes a lot more sense to me than a thermistor going intermittently bad and that somehow being fixed by removing power from the thermistor for a short duration. Next time it occurs, I'll beat on the top of the relay and see if that breaks it loose for confirmation.

In other words, at least in my case, the fan is the real problem. It's possible that the relay springs are just getting weak (in your case) but after probably over 10 years of regular use, I'm betting that the fan motor is showing more wear than that relay. BTW, mine's a 1992 GT. You didn't state the year of your car, I'm just guessing it might be the same generation.
 

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You're all wrong. The whole thing about the fan being bad is nonsense. And welding wires together? No. That's definetly wrong.

Siragan sez:

I think it may be your thermostat. If I'm not mistaken, your thermostat has a sensor that sends a message out to the ECU to turn the fan on once the coolant temp reaches a certain level. I'm not sure about this because I never have personally messed around with it, I'm just going by what I've heard.
 

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siragan said:
You're all wrong. The whole thing about the fan being bad is nonsense. And welding wires together? No. That's definetly wrong.

Siragan sez:

I think it may be your thermostat. If I'm not mistaken, your thermostat has a sensor that sends a message out to the ECU to turn the fan on once the coolant temp reaches a certain level. I'm not sure about this because I never have personally messed around with it, I'm just going by what I've heard.
the sensor is on the thermostat housing. I'm just trying to figure out the name of the sensor. I don't wanna go somewhere and say i need a sensor that goes on the thermostat housing. I know there is a couple and i don't wanna get the wrong one.....i'll see if i can take pics tomorrow to show the sensor i'm talking about.
 

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siragan said:
You're all wrong. The whole thing about the fan being bad is nonsense. And welding wires together? No. That's definetly wrong.

Siragan sez:

I think it may be your thermostat. If I'm not mistaken, your thermostat has a sensor that sends a message out to the ECU to turn the fan on once the coolant temp reaches a certain level. I'm not sure about this because I never have personally messed around with it, I'm just going by what I've heard.
Maybe welding is the wrong description. Anyway, if you run a lot of current through wires, or a relay (etc.), some force will hold those parts together. If you then cut the power at some other point the parts "welded" together will fall apart. So I'm saying the relay contacts are held together by this force. I think it is an electrostatic force keeping the wires together, but it could be related to the magnetic field and induction caused by the current flow through the wire. I'm not a physics major so I'm not for sure the exact force, however I do know that my theory is based on sound logic and scientific fact.

But let's not dwell on my answer, let's take a look at yours. So how does this sensor fail intermittently and the problem is solved by removing voltage to a completely unrelated circuit? It doesn't make any sense. He's just going to throw money at a problem, buy the wrong part (to fix the problem) and end up with the same thing happening some weeks or months down the road. I'd like to hear a logical explanation from you on how this bad sensor can cause the problem the poster and particularly myself are experiencing whereby removing and then replacing the fan fuse turns the fan off and it doesn't get stuck on for weeks or months at a time. I'll give you a hint about where in the circuit the power is cut by removing the fuse: only from the fan positive terminal before the relay. So in other words only the fan and relay are affected by removing the fuse. And then only the relayed side of the fuse; the relay will still switch on even with the fuse out.

Another possible logical cause for the fan remaining on but turning off simply by removing and replacing the fuse would be somehow voltage leaking from the relayed circuit (the actual fan leads) to the switching circuit (the ECU fan circuit) which would create a feedback loop holding the switch open. I'm not real sure how that would become only intermittent in nature though, so I'm still leaning towards my original answer.

Anyway, next time it happens I'll check the switching side of the relay for voltage. If there is no voltage, then my theory holds.

We're going to have to wait awhile for that to happen though, I've only had it happen twice in roughly 3 months/~6,000 miles.
 

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Superchkn said:
We're going to have to wait awhile for that to happen though, I've only had it happen twice in roughly 3 months/~6,000 miles.
How long have you let yours run before pulling the fuse? The fan is designed to run when the engine is off if the coolant is still too hot.

Siragan is right, it's not a problem with the fan. I think you're putting way too much thought into this. When you remove the fuse the relay's signal power will likely drop, which the computer probably picks up on and shuts off the fan.. when you re-insert it the relay isn't switched on anymore by the computer.

Most likely it's just the sensor/fanswitch/whatver,Idon'tknowwhatit'scalledeither in the thermostat housing causing the fan to run endlessly. Try disconnecting the sensor next time it happens. If it continues to run, short out the connector.
 

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How long have you let yours run before pulling the fuse? The fan is designed to run when the engine is off if the coolant is still too hot.
Let's put it this way, the ony time the fan ever runs after the car is shut off with the key out of the ignition is when it is stuck on. I've had the car 4 years and the first time the fan stuck on it was 40 degrees outside and stayed on until the fan was barely rotating and I had to push start the car. Thankfully I was on a hill. It stayed on for 3 hours, each time I parked on a hill so I could start the car. It never completely discharged the battery, just enough that I couldn't start the car. Finally I pulled the fuse and replaced it an hour later. The fan acted normally from that point on. The next time it happened I pulled the fuse for 5 seconds and replaced it, which was enough to do it. Let's put this another way, I've parked the car with the hot needle nearly pegged before and with the key out of the ignition, the fan won't run (so I had to put the key in the ignition and turn it to accessory). The computer isn't even in the picture despite what the manual may say.

Siragan is right, it's not a problem with the fan. I think you're putting way too much thought into this. When you remove the fuse the relay's signal power will likely drop, which the computer probably picks up on and shuts off the fan.. when you re-insert it the relay isn't switched on anymore by the computer.
How does the computer sense the voltage of the relayed fan circuit when it isn't connected to that circuit? The ECU is connected to the switching side of the relay which just activates a solenoid inside the relay which throws the much larger amperage switch that runs the fan. The circuits are not connected so if the power is cut to the fan, the ECU won't have any way to see it. I'm saying that the fan is drawing more power than it should which over time has probably heat-weakened the relay spring (which is supposed to return it to the off position). My relay shows visible signs of overheating. This results in the relay not being able to overcome the force holding the circuit on. This is compounded by the fact that the fan is drawing more amperage than normal which also increases the force required to turn seperate the contacts of the relay. You may think I'm full of it, but this force is why some high power breakers trigger an explosive to move the switch and thus cut the power in high amperage electrical systems. Search for "how stuff works" and breakers on google, such breakers do exist.

Most likely it's just the sensor/fanswitch/whatver,Idon'tknowwhatit'scalledeither in the thermostat housing causing the fan to run endlessly. Try disconnecting the sensor next time it happens. If it continues to run, short out the connector.
There is no voltage going to one of the sensors (which is a thermistor) when the car is off, this is the one the computer uses. I'm not sure how the other sensor works, but I'm pretty sure it is the sender for the temperature gauge. At least my car doesn't seem to care if it is disconnected. I'll try disconnecting it later tonight when I'm driving the car to verify (it's cold now and so the temperature gauge is pegged on "C").

Besides I still haven't heard logical argument supporting the ECT as the cause:
How would the engine coolant temperature sensor intermittently fail and why this would be fixed by removing voltage to a completely unrelated circuit.

I'm just saying that the ECT cause is contrary to the facts under more detailed scrutiny. I initially suspected the ECT but discounted it under more consideration of the circumstances surrounding the bizzare behavior of my car's fan.

My argument satisfies the facts, which include:
1) A relay that shows visual signs of overheating
2) A fan that is over ten years old and with a little knowledge and understanding of electrical motors I know it MUST be drawing more amperage than when it was new, likely considerably more amperage.
3) The fan comes on with the key off, which in 4 years has never happened before even when turning off the ignition with the fan running and the temperature gauge nearly pegged.
4) Disconnecting power to the fan, which only affects the relayed side of the relay circuit and is not visible to the computer or any other circuit, returns the system to normal operation and the fan does not stay on until some undetermined time in the future.
5) Zero voltage supplied to the engine coolant temperature sensor with the key off, proving the computer is not on and could not run the fan. Voltage is present however when the iginition is on and the sensor is sending the correct voltage (at least when tested hot and cold, I was unable to test the voltage during the fan episode). This fact completely removes the interaction of the computer from the argument. This alone should make you look towards another alternative cause, something relating only to the fan circuit itself.

I'm completely open to another explanation if it can satisfy facts 3, 4 & 5. Facts 1 & 2 just support my opinion of what caused 4 to happen.

[rant]
Please stop taking this as a personal attack. I provided arguments for my view and against the ECT as the cause. Siragan only provided an opinion with no basis why my argument is:

You're all wrong. The whole thing about the fan being bad is nonsense. And welding wires together? No. That's definetly wrong.
Thus discounting my argument without even considering it, or at least not offering any reasons why this is not a valid explanation as to why this is occuring. This was not posted in a polite manner in which the reason for why my argument was incorrect was presented. It was simply refuted for being ridiculous, which is/was personally offensive to me. Calling someones opinion nonsense is not a polite way to carry on a conversation.

My original post was presented, I feel, in a polite manner. If you or anyone else disagrees, please point out where I was offensive and I will change the way I post to the forums. I did not mean to offend or attack anyone or post in a way that could be construed as personally offensive.
[/rant]
 

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you may be right about completely obsolete circuts and all that fancy talk. On my 1989 LX, i had a similar problem, well the first time was the AC clutch went, and most of us know that when the AC is on, the Fan turns. Maybe just maybe your clutch isnt disengaging, and it just disengages when you unplug the fan, belive me...ive done it. I realized that if i pull the AC fuse no more fan probelms, and all of your temp sensors do get power, and send readings to your computer. regardless of what you think. Now dont get me wrong, you bring good arguments, really you do. But my point is the electrical thats on a car, is all intertwined, what some think affects this, will inturn affect a few others. Not always the case, but engine wise ive always been under the impression that all sensors work together to provide a smoother, more efficient running motor. Meaning maintaing your NOT (normal operating temp) is continuing with your fan...your fan will cool the coolant and motor as per its computers sensors. More times then none...espicailly on well my era of fords, But my point is all the sensors are interrelated one way or another. Now this coming from a 17 year old no one is going to listen, but im not a fool when it comes to working on cars. Now to answer tims question...listen to all these people, check every wire twice, make sure there are no rubs, no cuts, no kinks...etc. Make sure your connections are clean and tight, cuz we dont want any corrosion to be going on.
and about your fan turning on only when the car is off...you sure its wired right??? only reason being that it shouldnt be on with out power...maybe a break in the wire...these are only suggestions, (rememeber wires can break in the loom too so check them through out the WHOLE circut.)

none of this in meant to be taken in an offensive matter...im only trying to point things out, and give another perspective

8)

Dave
 

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It is true that shorts and the like can occur, but my main point is that the computer and the sensors with the vehicle off, are not getting any power.

That is to say, if I hook a voltmeter up to my engine coolant sensor while the ignition is on, it indicates power. When I turn the car off, the voltmeter reads zero volts. So the computer can't possibly turn the fan on when the ignition is off simply because it isn't powered except to keep the memory refreshed. (Well, unless the computer is hosed then all bets are off.) But that isn't my problem because as I said, I'm getting no voltage with the ignition off to the temperature sensor or any other engine sensor I've checked. The relay is hot by definition, just like the starter relay and the headlamp relay. I wasn't using my A/C so unless my car has demons the A/C sensors and relays couldn't be the problem. Really that only leaves the relay, since the switched side doesn't have any voltage (verified) with the ignition off. When the fan was running, I'm pretty certain there weren't any other sensors powered, but I didn't have any voltmeter to verify, hence the wait. Anyway, it sounds like Tim was suffering from a sticky relay (common problem) since after he unhooked the battery for 30 minutes and then reattached it, the fan started up again. On the next incident, just cutting the power was enough to do it. I'm not saying this electrostatic force can overpower a healthy relay spring, quite the contrary: it will only happen when the relay spring is weak or when the mechanism is sticky. Hence replacing the relay will solve the problem. But if the relay went bad due to another cause (such as a fan drawing too much amperage), then it will go bad again shortly. So, he should make sure his fan is in good working order too, unless he wants to keep throwing relays at it (though probably not at a quick pace, this last relay has lasted me over 2 years).

I like to keep it simple, I don't think a complex circuit is the cause of this, but not because I don't believe it can happen, but rather because I feel that is less likely a cause.
 

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blah blah blah........go get a damn haynes manual or w/e you prefer and look up the electrical guides in the back. Problem solved.

Side note:
Greg: he's right. I'm an electronic engineer major, welds frequently happen...

superchkn: You are wrong. Cant get welded. Why? Because the 2 positive and negative sources have to be touching for it to happen.
 

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92gt5spd said:
superchkn: You are wrong. Cant get welded. Why? Because the 2 positive and negative sources have to be touching for it to happen.
Isn't the point where the two circuits complete defined as the point where the 2 positive and negative sources meet?

Anyway the factory service manual isn't real helpful as it tests the relay for failing to activate rather than being stuck on. It sites the first likely cause of an always operating fan as being the relay, but also lists the circuit, ECA, motor, and switch. I'm not really clear on how the motor can keep the fan always running...but that's what it has listed.

So the manual isn't really helpful in its diagnostic chart since it is testing for the more common case where the relay fails to activate rather than the case when it won't deactivate (as far as the troubleshooting tree goes).
 

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well i fixed my problem. It was the sensor on the thermostat housing. The rounded end one. Try replacing that. It's a 20 dollar part at advance. I could even give a how-to on that later.
 

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Superchkn said:
92gt5spd said:
superchkn: You are wrong. Cant get welded. Why? Because the 2 positive and negative sources have to be touching for it to happen.
Isn't the point where the two circuits complete defined as the point where the 2 positive and negative sources meet?
Nope, thats "completing a circuit" When theres a component between the 2 sources, thats a circuit at work. In order to cause a weld you would have to short circuit the circuit. In which case the pos and negative would be touching each other directly causing a weld.

Now...Welding is not what causes relays to work. A relay works on magnets and electricity. A coil is inside it and when power is driven to it it becomes magnetic causing the contact point to be drawn to it which cause an output to go active or completing the circuit...ect. there are many types of relays, but they all work on electromagnetism
 

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Yeah, I know how a relay works.

Off-topic somewhat, but what causes a wire to stick to the can of an R/C motor when you complete the circuit from a 7.2volt battery pack? Whatever force holds that wire to the can is the force to which I'm referring. It takes some effort to remove the wire from the can while the power is supplied. However if I remove power from the circuit the wire just falls right off. Obviously some force is acting to keep that wire connected while power is applied, as I mentioned in my second post welding probably is not the correct term for that to which I'm referring.

The magnetic force created by the relay circuit closes the contacts on the high-current switched circuit. The current flowing through that circuit acts, in some manner, to hold the circuit closed even when power is removed from the circuit that creates the magnetic field to hold the contacts together. If I remove power from this "stuck" relay for even a few seconds, the relay returns to its proper open position, much like the wire falls off the can of my R/C car's motor when I removed power above. I suspect either the increased current draw of my fan causes this force to increase, or I think more likely a combination of a dirty relay mechanism and a heat weakened relay spring are causing my problem.

Anyway, I still fail to see how a temperature sensor that is not powered with the ignition off (verified by the 1992 Ford Factory Service Manual) can activate the relay in the first place, unless there is a short in the wiring somewhere that either powers the computer or the temperature switch. At least with my car, a powered computer (i.e. the ignition in the on position) will discharge the battery enough to prevent starting in about 4 hours. I doubt the temperature switch alone would cause any significant power draw, however it may end up powering devices higher in the circuit much like plugging a 12 volt power source into my cigarette lighter with the ignition off will turn on my radio :D I don't have a full wiring diagram available so it's hard to say.
 
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