ST1100 LLC leakage. how to separate FAN HARNESS

[Larry Fine]

Unless you need to read a specific voltage, a probe-type tester is much better for troubleshooting. Not only does it indicate power, you can clip the wire on battery + to test for grounds, too.

 

[dwalby]

A better test on these would be a 20 watt light bulb as the ohm meter will not test it for load capacity.

load capacity can be estimated from the resistance value. If the resistance is 0.3 ohms, then a 5A load is only going to cause a 1.5v drop and things should be OK. If the resistance is 2.0 ohms, then that same 5A load is going to cause a 10.0v drop and things will not be OK.

edit: I'm not saying the fan load is 5A, I don't know exactly what it is, I chose that number just to illustrate the calculation. I've checked the resistance before on this circuit on my own bike and I seem to recall it was about 0.7 ohms. If there is enough corrosion to prevent the fan from running, it will show up in a resistance measurement.

 

[ciliaris12]

yes, we're talking about the same thing.

Now, if for some reason the fan doesn't come on when you ground that connector, that's what I meant by checking the voltage at the connector with the ignition switch on. Put the (+) lead on the connector, and the (-) lead on the battery negative terminal. If you don't have something close to 12v between the connector and ground, then there is a problem in the electrical path to the connector.

The other way the electrical path can fail is if there's corrosion on the ground at the radiator. That will cause a voltage drop which prevents the fan from drawing enough current to run. To test that out put your multimeter in ohms mode and measure the resistance from the radiator ground point (the base of the thermo switch) and the battery negative terminal. That resistance should only be a few tenths of an ohm, something like 0.5-0.7 ohms or so, if its a lot more than that then there's something in the ground path that needs to be cleaned up.

hi dwalby
I just now tried if MOTOR FAN works when I connected CONNECTOR to the ground.
then it worked!
unfortunately no time to measures ohm or voltage.

now i proceeded remarkably, FAN MOTOR and FUSE system seems normal.
Also earthing BOLT seems no corrosion, off course it's my appearance check without disassembling.
Most likely I assume thermo SW is most doubtful.

i will try separating SW next time then I can see if it closes when temperature higher than 98℃, but i'mnot sure i can disassemble it or not.. no enough operation space available without detaching COWL...

 

[ciliaris12]

Unless you need to read a specific voltage, a probe-type tester is much better for troubleshooting. Not only does it indicate power, you can clip the wire on battery + to test for grounds, too.

hi Larry
thank you proposing
Yes I need to buy it , yes i will buy

 

[Larry Fine]

Don't disassemble anything. Try my suggestion.

With a tester's wire on battery +, the terminal on the temperature sensor switch should test as grounded when the engine gets hot enough to call for the cooling fan to turn on.

It's merely a temperature-activated switch. It does the same thing that you did when you manually grounded the connector. Your test actually shows that the thermal switch is bad.

 

[ciliaris12]

Hi Larry
yes absolutely you are right
originally i thought to disassemble and immerse the SW to the boiling water.
however your proposal sounds much easier for me

As i said , i assume SW have problem that it will never to close despite temperature over 85℃.
if my assumption correct, my MOTOR FAN should have worked. I hope it work today

 

[ciliaris12]

Hi
could anyone tell me how to separate this WIRE CONNECTOR from SW??

Yesterday my ST1100 had LLC leakage
during short touring. FAN-MOTOR didn't work at all.
I assume FAN MOTOR or its' fuse had some problem.

So i tried to separate the wire , then i wanted to connect to body for body-earthing. Because if SW has failure, direct earthing will make the MOTOR work.
But it's quite difficult to separate.

please anybody tell me how to do it.

I'm confused. please help me if someone have answer.
service manual says the thermo SW linearly works lower temperature than 85℃.
however almost all SW description is "SW closes above 85℃", no ohm action described below 85℃.

in ny memory, FAN did not linearly work below 100℃ am i correct?

and 85℃ is too much low temperature for engine to apply full FAN rotation. it will lose engine output.

I temporary ordered alternative SW instead lg 37760 MT2 003P just as trial. it's cheap only 5 dollars. it also says it will close at 85℃.
tomorrow I will exchange it.

 

[Larry Fine]

Two different things.

The fan is activated by a switch that is either on or off.

The temperature gauge is controlled by a variable resistor.

 

[dwalby]

I temporary ordered alternative SW instead lg 37760 MT2 003P just as trial. it's cheap only 5 dollars. it also says it will close at 85℃.
tomorrow I will exchange it.

as Larry mentioned, the thermo sensor resistance is what the temp gauge on the instrument panel uses for the position of the temperature needle. Its not the switch you're troubleshooting.

But, as you see in the spec, the switch shouldn't close until 98C, not 85C, so that switch will close way too soon and the fan will be on almost all of the time. It seems that the fan motor was designed for intermittent duty only based on the 98C switch, but you're running it full time with the 85C switch, so that could affect the fan motor reliability. And as you say it will also put additional electrical load on the alternator, which applies more engine load than is necessary.

BTW, you mentioned earlier in your first post that the fan didn't come on in normal riding, but you didn't mention if the temperature gauge went up into the red zone when the coolant overflowed. Can you provide a bit more info on the position of the temp gauge when it overflowed. The reason I ask is because if you overflowed with the temperature gauge at halfway or less, then the problem would likely be a split in the hose, not the thermo switch failing to do its job.

the fan switch normally closes when the temp needle goes a little past the vertical position and points slightly right of vertical.

 

[ciliaris12]

Two different things.

The fan is activated by a switch that is either on or off.

The temperature gauge is controlled by a variable resistor.

hi Larry
i thought water temperature gauge is allocated to just bottom of FILLER NECK,
so if service manual is correct, i think this thermo SW is just used for controlling electricity supplied for FAN MOTOR

however if memory correct, my ST1100 FAN is controlled on or off as Larry mentioned.
seems manual wrong.
but still 85℃ is far too much low...

 

[ciliaris12]

as Larry mentioned, the thermo sensor resistance is what the temp gauge on the instrument panel uses for the position of the temperature needle. Its not the switch you're troubleshooting.

But, as you see in the spec, the switch shouldn't close until 98C, not 85C, so that switch will close way too soon and the fan will be on almost all of the time. It seems that the fan motor was designed for intermittent duty only based on the 98C switch, but you're running it full time with the 85C switch, so that could affect the fan motor reliability. And as you say it will also put additional electrical load on the alternator, which applies more engine load than is necessary.

BTW, you mentioned earlier in your first post that the fan didn't come on in normal riding, but you didn't mention if the temperature gauge went up into the red zone when the coolant overflowed. Can you provide a bit more info on the position of the temp gauge when it overflowed. The reason I ask is because if you overflowed with the temperature gauge at halfway or less, then the problem would likely be a split in the hose, not the thermo switch failing to do its job.

the fan switch normally closes when the temp needle goes a little past the vertical position and points slightly right of vertical.

hi dwalby
here's a photo of overflow.
as posted to Larry, the water temp gauge iseems allocated to FILLER NECK lower position.
yes 85℃ is way too much low to work.

i tried again last night, and confirmed FAN didn't work even high temp.
my college also agreed that the FAN SW must have failure. need to exchange...

 

[dwalby]

hi dwalby
here's a photo of overflow.
as posted to Larry, the water temp gauge iseems allocated to FILLER NECK lower position.
yes 85℃ is way too much low to work.

i tried again last night, and confirmed FAN didn't work even high temp.
my college also agreed that the FAN SW must have failure. need to exchange...

the temp needle position in your photo isn't high enough for the fan switch to close. It has to get a little higher before the switch should close. Run it up to about halfway between where it is in the photo and the far right end of the white arc, if it doesn't come on then for sure the switch is the problem.

 

[kiltman]

i thought water temperature gauge is allocated to just bottom of FILLER NECK,

You can hook up an ohm meter to that switch, the positive to the switch and the negative to ground.. when the ohm meter reads between 10-15 ohms the fan will generally come on, the thermostat opens around the 45 ohm mark. ( that’s from memory I will edit and confirm once I look at my Clymers)

 

[ciliaris12]

You can hook up an ohm meter to that switch, the positive to the switch and the negative to ground.. when the ohm meter reads between 10-15 ohms the fan will generally come on, the thermostat opens around the 45 ohm mark. ( that’s from memory I will edit and confirm once I look at my Clymers)

thank you kiltman
i will try disassemble mine tomorrow. then i 'll check the ohm.
i think i can measure similar of it without disassembling but no time to try now

 

[ciliaris12]

i ordered genuine thermo SW just now
I can receive it tomorrow， very lucky

part number
thermo SW
37760 MT2 003
3830JPY

O-RING
9130761100
100JPY

THERMO SW is identical with my VFR800 RC46， it's interesting

 

[Larry Fine]

You can hook up an ohm meter to that switch, the positive to the switch and the negative to ground.. when the ohm meter reads between 10-15 ohms the fan will generally come on, the thermostat opens around the 45 ohm mark. ( that’s from memory I will edit and confirm once I look at my Clymers)

No, there are two separate sensors, a switch for the fan and a variable resistor for the gauge.

The load of the fan would likely burn out the gauge sensor.

 

[kiltman]

Yes there are two separate sensors. However, if you use the ohm meter instead of the temp gauge, on the thermo sensor (under the thermostat) you can confirm the parameters when a certain function is going to happen as designed by Honda.
On page 377 in Clymers there is a table for reference to what the coolant temperatures are in relation to what the resistance is of the thermo sensor.
When the system is just warming up, the thermo sensor resistance should be between 130- 180 ohms, at that time the coolant temperature is 50°C (122°F)
When the coolant is at 80°C (176°F) the resistance is 45-60 ohms
When the coolant is at 120°C (248°F) the resistance is 10-20 ohms.
At 80°C the resistance is 45-60 ohms that’s about when the thermostat should open (between 80-84°C or 176-183°F)
The fan should turn on when it senses the coolant is around 98-102°C ( 208-216°F)
The fan should turn off when the coolant is between 93-97°C (199-207°F)

If I recall correctly my fan would turn on when the thermo sensor registered around 30 ohms on the ohm meter. Or the 1 O’clock position on the temp gauge.

I provided this information as another way of determining if the system is functioning properly.

 

[Larry Fine]

Gotcha. That's very different than saying that the fan should come on because of the sensor's resistance.

 

[dwalby]

You can hook up an ohm meter to that switch, the positive to the switch and the negative to ground.. when the ohm meter reads between 10-15 ohms the fan will generally come on, the thermostat opens around the 45 ohm mark. ( that’s from memory I will edit and confirm once I look at my Clymers)

I provided this information as another way of determining if the system is functioning properly.

it was clear you knew the subject matter, but in your top post above you referred to the temperature sensor as a "switch", which may have confused the OP.

 

[ciliaris12]

the temp needle position in your photo isn't high enough for the fan switch to close. It has to get a little higher before the switch should close. Run it up to about halfway between where it is in the photo and the far right end of the white arc, if it doesn't come on then for sure the switch is the problem.

hi dwalby
the photo might be taken slightly after the phenomenon, but i think this level of water temp. is too much high enough to make the water boiling and overflow abnormally for ST1100. FAN shoud have worked more earlier. if i remember correctly, this is the highest temp. that i've seen on my ST1100.
i don't want to try much more higher situation, i think it's too risky. but i understand you believe it's not critical, thank you for your advice.