Flashing "cold" segment on Coolant Temperature Gauge?

Joined
Apr 13, 2017
Messages
4
Age
64
Location
Carlsbad New Mexico USA
Bike
2003 Honda ST 1300
I started my 2003 ST 1300 in near 100 F outside temperature and noticed far left "cold" segment on the Coolant Temperature Gauge was flashing. I rode 4 miles on the highway and 3 in town with a couple of stops at traffic lights. My bike sat in the shade for 3 hours​ then rode back home in 100 F heat. The flashing "cold" segment remained and the fan operated when appropriate and the engine seemed to operate properly. ( The little ovens on both sides of the faring where working well, a metal object in the left side was uncomfortable to hold in my bare hand, not unusual.)

The owners manual says the a flashing "hot" segment indicates and overheating engine condition. The Honda Service Manual tells how to test the sensor and light but I have not found anything about the flashing "cold" segment.
Any input on root cause and resolution would be appreciated.
:03biker:
 

CYYJ

Michael
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None any more.
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My best guess - not based on any knowledge of how Honda ST motorcycle temperature gauges work, but based on a general knowledge of how all microprocessor-controlled measurement systems are designed to self-test - is that a single flashing segment at the bottom end of the range means that the processor is not getting a credible (within acceptable range) signal from the temperature sensing probe. In other words, there's a wire loose somewhere between your temperature measurement probe and the instrument cluster. Another less-probable potential cause could be a failure of the temperature sensing probe.

If you rode back home in 100° F heat, I am sure that the engine reached its normal operating temperature. If all you saw on the engine temperature indication was a single flashing segment at the bottom of the range, that pretty strongly suggests that the temperature indication system is not working properly.

Michael
 

Blrfl

Natural Rider Enhancement
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Fast Blue One
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Flashing the first segment is a new one on me, and I can't find anything in either of the manuals about it. Michael's guess is as good as any.

The first thing to do is check for any stored fault codes, specifically code 7.

Second would be to remove the air box and disconnect the temperature sensor, which is mounted on the back of the thermostat housing. If the gauge shows hot (all bars) when you turn the ignition to on, you probably have a faulty sensor.

You can do a quick test of the sensor without removing it by measuring the resistance between the thermostat housing and the sensor terminal. There are three terminals in a triangle; the terminal you want is the one in the attached picture. Look for 2.1-2.6 kΩ Â± 10% at 68°F. I suspect that if the indication on that dash means the ECM saw something unrealistically cold, you're going to find much higher resistance than that and you'll know to replace the sensor.

You can also do a test with the sensor up to its threads in a pan of coolant on the stove at 248°F and look for 0.65-0.73 kΩ Â± 10%. If you remove the sensor, you will need to replace the sealing washer that goes with it. Also be aware that your wife may choose to replace you if she finds you cooking coolant in the pan she usually uses for hollandaise sauce. :D

--Mark
 

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Dusty Hotleg
Joined
Apr 13, 2017
Messages
4
Age
64
Location
Carlsbad New Mexico USA
Bike
2003 Honda ST 1300
Thanks for the instructions. The Honda service manual also describes the hot coolant on the stove method but did not tip me of to having a spare sealing washer handy. Thanks.
Why not just use water?
Also no mention​ of an unhappy wife. In my case , that does not apply. At present time I got 99 problems but a woman ain't one. I think I will use my old pan I keep in the garage and heat it on my gas grill anyway.
I will let the group know how it goes when I have a chance to start testing . Thank you all.
 
Joined
Mar 13, 2012
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soCal
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'97 ST1100
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dunno about the 1300 but the 1100 service manual gives resistance values at 50/80/120C (120C = 248F). So if you just use water and take the 50C and 80C readings that's probably sufficient to determine if the sensor is bad. You could also boil the water to ~100C and see if it looks reasonable compared to the 80 and 120C values, but its generally not going to be linear. Don't forget that altitude affects boiling point, so you could be a few degrees lower than 100C at boiling.
 
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