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1985 K100RS water temp gauge sender.

mcmlcccvrs

mcmlcccvrs

New member
Before I get ahead of myself installing a water temp gauge in my bike, I thought it prudent to test the resistance of the sending unit for the gauge to be sure it is okay as it is a used one. Is there a nominal resistance that these should display, for instance, at room temperature? Other than a partial BMW part number stamped on one of the hex sides, there is also the number 94 on another side. Is this an ohms measurement or something else unrelated?

As resistance is the inverse of temperature, should measured resistance truly go to zero at boiling point as the signal is being pulled to ground?

Just updating now that I've found my alligator clips. At room temp resistance stabilizes at about 796K ohms. After placing sensor into water being heated on the stove, it plummets to 1.5K-1.2K ohms.
 
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mcmlcccvrs said:
Before I get ahead of myself installing a water temp gauge in my bike, I thought it prudent to test the resistance of the sending unit for the gauge to be sure it is okay as it is a used one. Is there a nominal resistance that these should display, for instance, at room temperature? Other than a partial BMW part number stamped on one of the hex sides, there is also the number 94 on another side. Is this an ohms measurement or something else unrelated?

As resistance is the inverse of temperature, should measured resistance truly go to zero at boiling point as the signal is being pulled to ground?

Just updating now that I've found my alligator clips. At room temp resistance stabilizes at about 796K ohms. After placing sensor into water being heated on the stove, it plummets to 1.5K-1.2K ohms.
Click to expand...

I would guess that the "94" is degrees C (201 degrees F).

Ted
 
I'm interested in your project. Please keep us updated with photos if possible. Where are you installing the sending unit? Thanks.
 
6322 said:
I'm interested in your project. Please keep us updated with photos if possible. Where are you installing the sending unit? Thanks.
Click to expand...

Okay. I'll be sure to take photos and then post them all when done. The temp gauge sending unit is replacing the coolant drain plug. I'll be routing the sending unit wire through the engine block-same routing as the oil pressure switch I believe-to plug into the harness underneath the tank.
 
mcmlcccvrs said:
Okay. I'll be sure to take photos and then post them all when done. The temp gauge sending unit is replacing the coolant drain plug. I'll be routing the sending unit wire through the engine block-same routing as the oil pressure switch I believe-to plug into the harness underneath the tank.
Click to expand...

I installed temperature gauges on both of my K75s a few years ago but used new sending units since I didn't have any used ones, and I wanted to be confident they were accurate. You are on track for the routing of the wire to the sending unit. If I remember correctly, that wire goes to the temperature gauge and then you need another wiring harness that connects to the temperature gauge (and fuel gauge if you have one) and also to the main wiring harness.
 
GREGFEELER said:
I installed temperature gauges on both of my K75s a few years ago but used new sending units since I didn't have any used ones, and I wanted to be confident they were accurate. You are on track for the routing of the wire to the sending unit. If I remember correctly, that wire goes to the temperature gauge and then you need another wiring harness that connects to the temperature gauge (and fuel gauge if you have one) and also to the main wiring harness.
Click to expand...

To run the temp gauge sender wire the ignition cover and water pump cover have to be removed, which means draining the coolant. This is the only way to access the locations necessary to route the wire. I've actually got all that done but am still waiting on the fuel gauge/temp gauge harness which plugs into the ADDITIONAL INSTRUMENTS harness under the tank.

I don't believe my 1985 K100RS can accept a fuel gauge due to lack of correct harness and the 7L/4L method of displaying low fuel level. I stand to be corrected on that one.

I've taken a bunch of photos, and when I've wrapped this baby up, will do a little bit of a show-and-tell as Gary has asked for. Very straight forward though.

Tom
 
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Thanks Tom and others for your comments. Planning to do the same to my hack among other things this summer.
 
Okay, guys, I am up and running. I didn't get my harness until last Friday, installed it on Saturday and had to troubleshoot a non-functioning temp gauge which turned out to be the used temp sender I bought. Don't buy used sensors in my opinion. I just received the new temp sender this morning, installed it, and I now have a functioning coolant temperature gauge.

What I would like to know is this. Do I start a new thread in this forum so that this one doesn't get long-in-the-tooth, or go over to K-bike DIY and post everything there?

Tom
 
Tom,
Thanks for taking us through your installation. I'll be starting on my own soon. Not sure about moving it to DIY. I like it right where it's at. Take care, stay well and enjoy the ride.
gp
 
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