Thermo unit and thermo sensor replacement

[Mightymouse]

Hey,

I have a 1997 VMX1200JC. This will be the second year I have owned it. It's got about 63,000 miles on it.

I noticed two odd things since I've owned this bike regarding the coolant system.

1. Upon startup, the temperature gauge needle does not move as the engine warms up. When the engine is warm, I can "fix" the temperature gauge by tapping it. That'll get the needle to move.
2. On a hot day in traffic, sometimes the engine stalls if I'm not moving.

These symptoms made me wonder if the thermo unit (part #11H-83591-00-00) and thermo switch (part #3LN-83560-01-00) were bad.

I removed both from the coolant manifold and tested each per the procedure in the Claymer manual (pages 344-345) (ISBN-13: 978-1-59969-650-8).

I discovered the thermo unit was bad. The resistance was greater than the specifications listed in Table 2. I ordered a new one.

I was unable to determine if the thermo switch was bad. I could not get the coolant hot enough to test the continuity of the switch (221 degrees F).

So, I reasoned if the thermo unit was bad, there may be a chance the thermo switch is bad as well.

So, I ordered a new one.

Partzilla.com charged $104 for both. Shipping and taxes included.


Now I'm waiting for the parts to come.


Has anyone else gone through this? Do these thermal sensors go bad with age?

 

[Mightymouse]

And uh....how do you use a micrometer to test the water temp gauge?

 

[maleko89]

The thermoswitch is for the radiator fan. As long as the fan pops on before it gets to the red line on the temp gauge, it's fine. The thermo unit (smaller of the two) is for your temp gauge. I've never seen one go bad. Usually it's either the gauge itself or the ground wire which attaches to the top of the coolant manifold near the coolant cap.

Mark

 

[sdt354]

A multi-meter with a thermal adapter me thinks.

 

[Mightymouse]

The thermoswitch is for the radiator fan. As long as the fan pops on before it gets to the red line on the temp gauge, it's fine. The thermo unit (smaller of the two) is for your temp gauge. I've never seen one go bad. Usually it's either the gauge itself or the ground wire which attaches to the top of the coolant manifold near the coolant cap.

Mark

Thanks. I'll take a look at the ground wire. There might be some corrosion where it connects to the coolant manifold.

I thought the gauge might be suspect as well. I lightly sanded the electrical terminals that connect the thermo unit to the water temp gauge. The continuity of each wire was good.

I'll let ya know how it goes.

 

[Mightymouse]

A multi-meter with a thermal adapter me thinks.

That'd be a sweet tool to have.

 

[[email protected]]

And uh....how do you use a micrometer to test the water temp gauge?

It looks like you could connect a 12VDC source to the gauge where the BR wire attached.
You would then need to run a wire from the GR terminal to a variable resistor (potentiometer) that you can tune between 20 OHM and 160 OHM and land it on a ground.

Apply power and adjust the resistor to check gauge function. There is nothing in the manual that correlates a certain temp with a certain gauge reading but, if you have low resistance in the circuit (26.2-29.3 Ohm) the gauge should be up by the red zone as this would be a temp of 212F. If you raise the resistance to 153.9 ohms the gauge should be way down at the bottom as this would be a temp of 122F.

 

[sdt354]

That'd be a sweet tool to have.

Or an infredheat gun will do the trick. Harbor Freight has them cheap.

 

[Mightymouse]

It looks like you could connect a 12VDC source to the gauge where the BR wire attached.
You would then need to run a wire from the GR terminal to a variable resistor (potentiometer) that you can tune between 20 OHM and 160 OHM and land it on a ground.

Apply power and adjust the resistor to check gauge function. There is nothing in the manual that correlates a certain temp with a certain gauge reading but, if you have low resistance in the circuit (26.2-29.3 Ohm) the gauge should be up by the red zone as this would be a temp of 212F. If you raise the resistance to 153.9 ohms the gauge should be way down at the bottom as this would be a temp of 122F.

It looks like you could connect a 12VDC source to the gauge where the BR wire attached.
You would then need to run a wire from the GR terminal to a variable resistor (potentiometer) that you can tune between 20 OHM and 160 OHM and land it on a ground.

Apply power and adjust the resistor to check gauge function. There is nothing in the manual that correlates a certain temp with a certain gauge reading but, if you have low resistance in the circuit (26.2-29.3 Ohm) the gauge should be up by the red zone as this would be a temp of 212F. If you raise the resistance to 153.9 ohms the gauge should be way down at the bottom as this would be a temp of 122F.

That's a great idea. Thank you very much. I'll give it a go.

 

[Mightymouse]

The new thermo unit arrived. I installed it and the gauge worked. Looks like the problem is fixed.

I will still double check with mabdcmb's suggestion and test the gauge itself to be sure.

 

[Fire-medic]

Geez, next time do a search on here for cheaper replacements, substitutions have been posted on here for our thermostat, the radiator cap and the thermal switch, much cheaper than OEM parts.

https://www.vmaxforum.net/threads/different-thermostat.1841/#post-11135

Some info on the coolant drain petcock, often a subject of debate: "how-doe it work? How do I set it?"

https://www.vmaxforum.net/threads/drain-cock-valve-assembly.7351/page-2#post-469283

Coolant system info, including Sean Morley's as-usual helpful comments:
https://www.vmaxforum.net/threads/too-hot.4511/#post-43161

https://www.vmaxforum.net/threads/leaky-cooling-sys.34449/#post-370477

https://www.vmaxforum.net/threads/too-hot-to-handle.19022/#post-208104

There are more, search (advanced) is your friend.

 

[Mightymouse]

Thanks Fire-medic, those are good links.

 

[Fire-medic]

Next-time you see a question you know the answer to, you can direct the OP to what you previously-read. Pretty-much any issues you encounter are probably already written-about on here, somewhere. I learn all the time from other members.

 

[Mightymouse]

Will do.

 

[Mightymouse]

Update: Replacing the thermal unit did not work. I let the bike warm up but the coolant gauge did not move. I tapped it a couple times and then the needle moved.

The only thing I haven't replaced is the gauge. Is anyone selling a working gauge cluster by any chance?

 

[one2dmax]

You likely have a bad gauge if you've already checked the connections. I have clusters or even just the tach/temp internals (easy to swap).

 

[timeout43]

I have come across a few gauges doing the same thing, sticky needle in the gauge

 

[Mightymouse]

You likely have a bad gauge if you've already checked the connections. I have clusters or even just the tach/temp internals (easy to swap).

A swap may do the trick.

 

[Edward]

Update: Replacing the thermal unit did not work. I let the bike warm up but the coolant gauge did not move. I tapped it a couple times and then the needle moved.

The only thing I haven't replaced is the gauge. Is anyone selling a working gauge cluster by any chance?

Make sure the wires are inserted completely in the back of the gauge. As Firemedic said on another post, unplugging and plugging connectors is a good PM item.
It's a likely cause if the bike has ever seen rain.

 

[Mightymouse]

Make sure the wires are inserted completely in the back of the gauge. As Firemedic said on another post, unplugging and plugging connectors is a good PM item.
It's a likely cause if the bike has ever seen rain.

Good suggestion. Yup, checked all of that. I even sanded the contacts and applied a little dielectric grease to make sure everything was making good contact. So I ruled out that possibility.