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Cooling fan comes on too soon, stays on


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1994 Subaru Legacy. On cold start, cooling fans are off. As the engine heats up, the cooling fan comes on and stays on. The temp guage shows normal temperature.

 

If the cooling temp sensor was bad, wouldn't the temp guage also be off? But the temp guage reads just like it always has.

 

Not quite sure where to go from here.....

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If the cooling temp sensor was bad, wouldn't the temp guage also be off?
first, there are 2 temp sensors,

one for the computer and one just for the gauge.

 

but one fan, driver side, comes on with the AC,

so if the defrost is on then the AC is on and the fan will come on.

 

which fan comes on and stays on, passenger side?

this is the one that should come on when needed for cooling.

 

how is the coolant level in the over flow bottle?

in the radiator?

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TWO sensors hahahahahah. That makes SO much more sense! The Chiltons manual is rather ambiguous about the temp sensors and doesn't give a good description of what they do. Haynes does a much better job describing them, and even shows a good picture of the two sensors, one right next to the other. This isn't the first time the Chiltons manual has let me down, I think it's going to have an encounter with the recycle bin soon. I should have looked in the Haynes manual first.

 

For the money and effort, I'm just going to replace the sensor for the computer. I'm betting 99.8% that replacing it fixes the problem, based on the symptoms I'm observing.

 

I'll post the results here.....

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PS the coolant level in radiator is at the cap, coolant bottle is near the top line where I left it a few months ago. As the engine heats up, the one fan comes on before the engine gets to full operating temperature and stays on. My guess the sensor has failed and triggers at a temp lower than the thermostat setting. Since the coolant temp never drops below the thermostat setting, the fan never shuts off.
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OK, now I'm stumped. I replaced the sensor. I run the engine. Just before it gets to the point where the thermostat opens and the coolant temp stops to rise, the fans come on - both of them. If I shut the engine off long enough for it to cool a bit, they stay off. I start the engine, it and warms up, and it seems as if the temperature that the fans come on is right below the temperature at which the thermostat opens, and so the fans - both of them - run continuously.

 

The cooling system is full, no bubbles, no leaks. And the heater/defrost/ac is off.

 

My next step is to replace the thermostat - but I'm not sure what good that will do, except it's a cheap one and i have a better quality one sitting on my bench that is brand new, and here in Phoenix, cheap thermostats is a bad thing. Cause summertime temps routinely top 110, day after day, week after week.

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so let me ask you a question,

how does this cooling fan problem keep you from driving your car?

 

in other words,

the fans come on too early.

that is WAY better than too late,

and it in no way affects how or when you use your car.

so what's the problem?

 

btw: the t-stat MUST be a subaru item.

aftermarket will cause you headaches.

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so let me ask you a question,

how does this cooling fan problem keep you from driving your car?

 

in other words,

the fans come on too early.

that is WAY better than too late,

and it in no way affects how or when you use your car.

so what's the problem?

 

btw: the t-stat MUST be a subaru item.

aftermarket will cause you headaches.

 

1) It didn't used to be this way

2) The fans will wear out prematurely

3) Excessive load on the alternator

 

4) It's not a subaru tstat, but a cheap O'Reilys tstat, from before I learned not to by parts from O'Reilys. I foresee a visit to the Subaru dealer in the immediate future to get a suby tstat. Be surprised (but not too surprised) if that fixes the problem

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which temp sensor did you replace, the two wire one or the one wire one?

 

I replaced the two wire sensor. The one wire sensor is for the temp gauge only.

 

But the story gets better. As I'm checking the new sensor to make sure it isn't leaking, I notice coolant dripping from the corner of the radiator. Surprise surprise the radiator leaks. Great. Merry freakin' Christmas, I get a new radiator under the tree. It wasn't much of a leak, the overflow tank was still half full, but ya gotta fix these things while you can because a leak today can turn into a blown engine tomorrow.

 

Went to the Subaru dealer and bought a factory thermostat and radiator cap. Examine factory thermostat. Examine AutoZone cheap made in China cr*p thermostat. Notice the factory thermostat weighs twice as much as the cheap Autozone cr*p thermostat. Note to self - always use factory thermostats, never use cheap made in China cr*p thermostat.

 

So now I have a brand new radiator, new factory thermostat and radiator cap, water pump was new a few months ago, thermo sensor is new. Haven't had a chance to put it all together yet

 

I don't know at what temperature the fan is supposed to come on, I have not found it documented anywhere. There is minimum coolant temperature maintained by the thermostat, and there is another temperature that is higher than this that triggers when the fans come on. The temp sensor tells the ECU what the temp is, and when it reaches a certain level the ECU tells the fan to come on. If the ECU thinks the fans should come on at a temp that is less than that maintained by the thermostat, the fans will run all the time. They did not used to do this. If it still happens, about all that is left is a bad ECU or a wiring problem between ECU and sensor.

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Hello;

When the radiator has a small leak the system is not under pressure. This allows the temperature to rise, equals running fans. Check the heater and small hoses going to the air intake, IACV for leaks. The fan should come on about 210-215 and go off at 190-195 degrees. Put it all together and the problem should go away, Steven.

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Hello;

When the radiator has a small leak the system is not under pressure. This allows the temperature to rise, equals running fans. Check the heater and small hoses going to the air intake, IACV for leaks. The fan should come on about 210-215 and go off at 190-195 degrees. Put it all together and the problem should go away, Steven.

 

I guess that makes sense, even though it was a small leak. And it definitely leaked, though I never noticed the temp sensor showing a higher temp, and it didn't even drain the overflow tank, and there was no air that I'm aware of in the system. When I pressure tested it, the pressure came right up - it doesn't come right up that fast when there is air in the system.

 

Well, I can't argue with a leaky radiator - I guess it doesn't have to make sense....I have a new radiator, new Subaru thermostat, new Subaru radiator cap, newish water pump. I replaced all of the heater hoses with Subaru hoses a few months ago, likewise the air hoses. Even new Subaru belts. They cost a bit, but heck, the factory Subaru hoses lasted 20 years, I've never replaced them before. Still haven't had time to put it all back together, hopefully that will happen tomorrow. It's a quick job, but RL keeps getting in my way.

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So I put it all back together. filled the cooling system via the top hose as others have suggested to minimize the amount of "burping" necessary. Start engine. Warms up. Thermostat opens. A few minutes the fans come on. They run a minute, and shut off. Five minutes later they turn on, run a minute and turn off. Repeat. And the temperature gauge does not seem to move when this is happening. I think the range of temperatures between thermostat opening and fans coming on is correct but not really enough to tell by the temp guage unless you are watching closely.

 

I'll take out on the road tomorrow and see how it does....but sitting at an idle in my garage, the fans cycle on and off like you would expect.

 

And do you know what happens when you buy a non-Subaru radiator? You get a made-in-China radiator that has the wrong drain plug in it and won't seal. Leaked like a sieve. Had to cut off a 1/4 inch of the original Subaru plug and use that instead. That one secured and sealed like it was supposed to. Quality control at its finest.....what happened to the days when we could go to the parts store and get good quality made in America parts, or at least Made in Japan parts for our cars? It seems that that Autozones and all the rest of them only sell made in China junk.....

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i got a spectra radiator for my gt a while back. good build, nice quality. made in canuckistan, not china. when the radiator in my wagon goes, im going to get the gt version spectra for it as well. the gt one is beefier than the L one. im pretty sure its 2.5l vs 2.2l tho, not the model.
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