Coolant fan issues

[Joshsbk]

I just got my first Brick, a 1985 K100 and when I got it home I noticed the fan was not turning on. After researching on this forum I jumpered the cooling fan relay at 15 and A2 and the fan came on. I then sent "E" to ground and the fan turned on. So the relay works. What I figure now is I have a bad water temp sensor. My question is how can I test the temp sensor without replacing it? Also I know the sensor also runs into the fuel injection controller, is there any chance that could be bad, or does the signal from the sensor split and go to the controller and the fan relay at the same time? Also I have a jumper in the 15 and A3 lines so the fan just runs all the time for now so I can ride. Is there any harm that can be done by doing that? Appreciate the help I have already found on this forum!

[volador]

Welcome

Temp sensor on coolant 'T' into engine block test for resistance either sensor 'spade terminals' to sensor body measures ≅ 2.5KΩ @ 20°C

test pins 10 and 5 on the ECU connector plug under the seat for resistance measures ≅ 2.5KΩ @ 20°C
Flat blade screwdriver, 'lever forward' in the hole of the tool-tray to loosen ECU connector plug

check the wires from Pin 10 & 5 of the fuel injection control unit plug for open or shorts

Pin 10 - violet/green
Pin 5- brown

more about Jetronic diagnosis http://www.motobrick.com/index.php/topic,13440.0.html

Run the fan all day & night long until it dies or melts

[Joshsbk]

Am I correct in assuming that I could do a resistance test right at the temp sensor terminals to check the sensor itself and then perform the same test at ECU connector to check the wires and sensor seperately?

[volador]

Correct

[Laitch]

Am I correct in assuming that I could do a resistance test right at the temp sensor terminals to check the sensor itself and then perform the same test at ECU connector to check the wires and sensor seperately?

Performing the resistance test at the fuel injection control unit will be a less complicated way to obtain the full range of sensor values from cold engine to hot. Some remove the sensor altogether, dunk its stem in boiling water and measure resistance as the water cools. Measuring the sensor's range where it's installed will be interesting. You must determine the full working range of the sensor.

[K1300S]

are you sure it is not working?  the fan kicks in a lot higher on the temp gauge than you would think.......like when the needle is at the start of the red.

[Joshsbk]

Sorry got busy with life and didn't get back to this until today. I checked the coolant sensor and the ohms never dropped from the ambient temperature so I'm pretty sure that is bad so I just replaced that. However I installed a fan bypass switch which made the fan work for the time being when I felt it needed it but noticed the fan was noisy some times and today this week it gave out on me, so I'm also going to change the motor portion out. I bought my bike already turned into a cafe racer so I don't have a temperature gauge. On a side note, when I went to drain the coolant instead of having a drain plug I had a "air /water sensor" and that broken in half on removal (I promise I'm not a monster just breaking everything in my bike haha). What I thought was weird is this sensor was supposed to just be a drain plug and no wires were going to it. Can I just replace it with a M10x1 screw and call it good?

[Laitch]

What I thought was weird is this sensor was supposed to just be a drain plug and no wires were going to it. Can I just replace it with a M10x1 screw and call it good?

Not weird. That outlet serves as mounting point for either a drain plug or a temperature sensor for a water temperature gauge mounted in the fairing.

Replace it with the M10x1. I'd use copper anti-seize on its threads and use a zinc-plated screw if possible.

You could change the fan's motor, or you could replace the whole thing with a 6.5" Spal puller fan. Here's a post with a link to a Spal fan conversion. Here's another description.

[Joshsbk]

Awesome thanks! Drain plug ordered. I may look into getting a sensor to put in it later on once I decide if I want a analog gauge for it or maybe something fancier that would integrate into a motogadet.

Good call on the fan conversion, unfortunately I already ordered the motor so I'm gonna keep that as a project for if it goes out again.