Author Topic: Cooling fan coming on at very low temperature  (Read 240 times)

Offline alexg

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Cooling fan coming on at very low temperature
« on: September 13, 2020, 04:02:28 PM »
Hi:
I want to see if any of you have had this problem. Before I take the temp sensor out and try to "heating over a stove to see the change in resistance" method, was wandering if the same symptom can be caused by faulty grounds?

I have temp gauge and is staying in the middle, and the overheat light did not come up.

Thanks...

Alex
  • Michigan
  • '93 K75S, 1975 BMW R75/6 & 1984 Yamaha RZ350
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Offline Laitch

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Re: Cooling fan coming on at very low temperature
« Reply #1 on: September 13, 2020, 04:15:21 PM »
Let's try again.

Does the fan cycle off then on repeatedly? You can follow the troubleshooting guide's LE-Jetronic Test on Pin#10 to see how the data squares up before removing the sensor and immersing its probe in boiling water while using a multimeter and thermometer to record its cool-down resistance.
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Offline alexg

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Re: Cooling fan coming on at very low temperature
« Reply #2 on: September 13, 2020, 05:03:56 PM »
Laitch:
Thanks for the reply. It cycles on and off while warming up, and then  stays solid on as soon as the engine is somewhat warm. Where is pin #10? Is that coming from the temp sensor to where?

Thanks again.
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Offline Laitch

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Re: Cooling fan coming on at very low temperature
« Reply #3 on: September 13, 2020, 05:13:54 PM »
Where is pin #10? Is that coming from the temp sensor to where?
That's on the Jetronic plug under the seat. You measure at the pin's socket, not the pin itself.  Click on the link at the bottom of johnny's post in this section. You'll find the test in that pdf.
  • Along the Ridley in Vermont.
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Offline alexg

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Re: Cooling fan coming on at very low temperature
« Reply #4 on: September 13, 2020, 08:25:13 PM »
Got it ! Very nice write up about testing a bunch of stuff. I will try tomorrow with the bike cold and then at normal temperature and compare to those values.
Thanks,
Alex
  • Michigan
  • '93 K75S, 1975 BMW R75/6 & 1984 Yamaha RZ350
Alex G.

Offline alexg

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Re: Cooling fan coming on at very low temperature
« Reply #5 on: September 14, 2020, 11:32:00 AM »
Ok Laitch et al:
I have done some measurements on pin #10 from the EFI connector:

At room temperature 25C: 2kohm
At the middle of the BMW temp gauge: 213 ohm
At fan start: 185 ohm

During fast idling, the fan cycled on/off like it always have done. I am wondering it this can be either a short somewhere or lack of ground, as the temp sensor seems to be working fine. I will clean all the ground points and see what happens. Do not want to start fixing what is not broken.

Any other suggestions?

Thanks,

Alex
  • Michigan
  • '93 K75S, 1975 BMW R75/6 & 1984 Yamaha RZ350
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Offline Laitch

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Re: Cooling fan coming on at very low temperature
« Reply #6 on: September 14, 2020, 01:01:18 PM »
During fast idling, the fan cycled on/off like it always have done. .
Can you clarify this statement? Under what conditions and for what duration is the fast idling done?

So far, I see no problem indicated in the coolant temperature sensor with the numbers you've developed. From what I've read here, these temperature gauges seem to vary somewhat from moto to moto where the needle points during normal operating temperature. Maybe others here will chime in.
  • Along the Ridley in Vermont.
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Offline alexg

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Re: Cooling fan coming on at very low temperature
« Reply #7 on: September 14, 2020, 01:13:49 PM »
The fan turned on when the temp gauge got to 3/4 and off when the needle moved back a little. The cycling on/off was definitely related to temperature fluctuation and not to any random electrical event. Otherwise, normal.

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Online The Mighty Gryphon

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Re: Cooling fan coming on at very low temperature
« Reply #8 on: September 14, 2020, 01:17:23 PM »
The part of the temperature sensor that controls the mixture appears to be working okay.

There is a second output from the sensor that controls the fan.  That is on a violet/green wire that goes to the temperature relay in the relay box.  The problem may be in that section of the sensor or in the relay that turns on the fan. 

I think that the temperature response of the second sensor is that same as the one for the ECU.  ~2500 ohms at 70F and ~250 ohms at 190F.  You need to get into the relay box and pull the temperature relay and check the resistance to ground on the pin with the violet/green wire.  It should match what you saw on pin #10 at the ECU.  If not, I would suspect an issue with the temperature relay.

Edit:  The post you put up while I was typing indicates that everything is working properly with the fan.  When riding the airflow is enough to prevent cycling, it's only when you stop after a hard run or in stop and go traffic on a hot day that the fan will usually cycle.
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Offline alexg

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Re: Cooling fan coming on at very low temperature
« Reply #9 on: September 14, 2020, 01:28:45 PM »
Mighty:
That is a good idea, thanks! Both output pins should have the same resistance to ground.  Will warm up the bike again and check both at the temp relay and ECU.

One question though: why do you say that if the resistance is not the same, there would be an issue with the temp relay? Would it not be a problem with the temp sensor?

Alex
  • Michigan
  • '93 K75S, 1975 BMW R75/6 & 1984 Yamaha RZ350
Alex G.

Offline Laitch

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Re: Cooling fan coming on at very low temperature
« Reply #10 on: September 14, 2020, 01:29:06 PM »
The fan turned on when the temp gauge got to 3/4 and off when the needle moved back a little. The cycling on/off was definitely related to temperature fluctuation and not to any random electrical event. Otherwise, normal.
As long as the engine is idling, cycling on and off is what the fan is going to do. Stabile cooling results from increase in RPM and airflow through the radiator. The cooling system should have sufficient coolant and be relatively free of particulates.

The thermostat plays a role in all this and should be opening and closing at correct temps, too but I can't discern a particularly troubling symptom yet. Is this behavior recent?
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Offline alexg

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Re: Cooling fan coming on at very low temperature
« Reply #11 on: September 15, 2020, 01:18:14 PM »
Hello Laitch and other fellow brickers:

The subject problem has not repeated. It occurred only once last Sunday.

Following the suggestions received, I got the tank out and in a few times while the engine was warming up from room temperature all the way to when the fan kicks in. I measured the resistance to ground on pin #10 at the ECU connector and to pin E on the fan control module. Within a couple of ohms, they mirror each other pretty well, so the temp sensor is working fine.

I have cleaned the grounding points, just in case, but I do not see any reasons why the subject problem occurred in the first place.

Any suggestions are welcomed. On the bright side, this is not an issue that will leave me stranded, but being Type AA, I would like to get to the bottom of it.

Alex
  • Michigan
  • '93 K75S, 1975 BMW R75/6 & 1984 Yamaha RZ350
Alex G.

Offline Laitch

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Re: Cooling fan coming on at very low temperature
« Reply #12 on: September 15, 2020, 01:44:49 PM »
Any suggestions are welcomed. On the bright side, this is not an issue that will leave me stranded, but being Type AA, I would like to get to the bottom of it.
I'm not an enabler so suggest that you use this one-off experience as a chance to develop other facets in your personality like equanimity and transcendence.  :laughing4-giggles: There is no bottom.
  • Along the Ridley in Vermont.
  • 1995 K75 80,000 miles
I wept because I had no radials until I met a man who had no splines.
https://tinyurl.com/RillRider

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