Speedometer Temperature Gauge on a '93 CB400 Super Four

[chanzhf]

Here's a picture of the clocks. The bottom one is the original Japanese ones, which as you can see, has probably seen better days. The top one is Chinese-made, which I've run through about 1500km. It appears to be pretty much plug-and-play. I am not sure if I am missing something out about the temperature gauge on the clocks not working.

As for the parts list, that booklet is simply a godsend. I read Japanese so it makes things slightly easier. part 24 of F-31 refers to the thermo unit, and part 25 which is known as the thermo switch assembly. If someone would be able to give more information on them, I could try and work around to see if replacing those thermos might be a solution.

[royster81]

The price attracted me yeah as I'd been looking at getting a superfour for years and had finally decided to go get one and stop talking about it , so I'd been on Gumtree etc etc and yours was just one of many I missed out on

I suggested a transplant to my mate but his clocks where wrecked and beyond use, I'd be interested to see if that works on yours if you do it.

[chanzhf]

@Devon462 I think you might be referring to the thermostat that switches the radiator fan on. My radiator has no thermostat I believe, rather, it is connected to a manual switch. I'm not sure if it was meant to be that way as it has been like that when I got the bike.

As for the radiator panel guard and side guards, these were bought directly from China. About the equivalent of £30 for the both of them. (I believe aliexpress is more pricey)

[Devon462]

@chanzhf Yeah after looking at it this morning the wire goes from the sensor direct to the fan. My mistake.

[SevenThreeSeven]

When I talk about the bike's "thermostat" I'm talking about the mechanical valve that is heat-sensitive (it contains a wax core that expands when heated which opens a flow-pathway for the coolant to cycle through the radiator).

I took a look at the Superfour cooling system in the translated-to-english-by-a-Russian-speaker manual: The temperature sensor that is supposed to be connected to the instrument panel gauge is located in the same metal housing that has the radiator filler neck/cap at its top and the mechanical thermostat inside. In the pictures of the various SF models this housing is located above the cam cover, just in front of the airbox. The temperature sensor is either screwed into this metal housing on its left hand side or backside.

The temp gauge on the SF instrument panel operates this way: the gauge is always/continuously fed 12 volt power from the bike's wiring harness. When the bike's coolant is cold this 12 volt power can't go anywhere (it can't "flow"). As the bike's coolant heats up the temperature sensor mounted on the thermostat housing will begin to allow more and more of that 12 volt power to flow through it into the metal body of the thermostat housing. This gradual increase in the flow of 12 volt power will cause the temperature gauge needle to move/deflect toward a hotter indication.

[chanzhf]

@SevenThreeSeven

I did some reading on my own. Thanks for explaining. I know which one you are referring to.



Would you be able to throw me a couple of reasons the gauge needle is not moving?

A faulty thermostat unit could be a reason, one that I'm gonna try and get checked out later.

Another reason could be a faulty gauge in itself.

And of course, a faulty temperature sensor.

[royster81]

So if you were to apply 6v-9v-12v to the wiring to each gauge (the old Honda one and the Chinese one) and see where the needle moves to you could figure out if the resistance is off at the needle end or the gauge is faulty

[royster81]

I'll check have i a spare thermostat housing you could borrow the sender out of

[SevenThreeSeven]

There are several ways this situation could be screwed up:

1. The Chinese guy who did the wiring of the replacement instrument cluster might have been confused or misinformed. The Chinese replacement instrument cluster is set up with multi-pin connector plug(s) that mate into the original Honda wiring harness, right? If so you need to carefully verify that all of the individual pins for each wire in the connector plug is/are mating to the correct pin on the plug in the Honda wiring harness.

2. Another failure cause could be a poor path-to-ground situation occurring at the Honda temperature sensor (on the thermostat housing). If the bike's wiring harness wire that attaches to the temperature sensor is loose or corroded or cracked it might not be capable of flowing any current through the temperature sensor (when the coolant is hot).

(info: if you want to test the Chinese instrument cluster temperature gauge: Step 1 is to determine if the gauge is receiving 12 volt power when the bike is key-switched to "ON" and/or when the engine is running. Get a multi-meter and set it to the DC volts range, put the negative (black) probe on the bike's battery negative pole and put the positive (red) probe on the solder connections for the temperature gauge (there should be two, maybe three solder connections that apply to the temperature gauge: a 12 volt supply, a path-to-ground that runs to the bike's temperature gauge, and maybe a third wire that would be a ground for the gauge's lighting, if there's any). You should find 12 volt power on one of those lines. Step 2 (if you confirm that 12 volt power is being supplied to the gauge) is to cause the temperature needle to deflect to full HOT by "jumpering" the path-to-ground that is normally connected to the bike's temperature sensor. All you need to do is connect a wire directly from the connector that attaches to the bike's temperature sensor to the battery's negative pole. This will provide a full-flowing path-to-ground for the 12 volt power that is being supplied to the Chinese instrument cluster temperature gauge and the gauge's needle should deflect to full HOT.)

3. Also, I noticed in several of the SuperFour Service Manual wiring diagrams that the bike's thermostat housing has its own ground wire that grounds back into the bike's wiring harness (I think 2 out of 3 total wiring diagrams showed this feature). On some bikes the path-to-ground of the temperature sensor is simply left to the metal bolts that connect the metal thermostat housing to the bike's frame. That's usually good enough (that's how my Suzuki GSF400 and Kawasaki EX250 are set up). But sometimes the manufacturer isn't confident that this path-to-ground will be adequate, possibly due to the metals involved or some other oddity in the bike's frame construction. In those cases the manufacturer will add a grounding wire to the thermostat housing. If your SuperFour is one of the sub-model types that has a thermostat housing ground wire you need to confirm that this wire is properly connected.

[chanzhf]

@royster81 Cheers mate that's very kind of you. Give me a shout if you have a spare working sender I could test with.

@SevenThreeSeven Thanks so much for the very detailed troubleshooting response. I would very much like to believe it is as simple as a wiring problem where the chinese instrument wires are not matched up correctly to Honda's original wire harness. I didn't have time to troubleshoot today as I was busy placing a new centre stand on the bike.

I will troubleshoot them tomorrow and report back with the results. Hopefully I'll have a working temperature gauge by tomorrow, fingers crossed.