Electrical Issue - Engine Temperature Gauge?

Kewaneh

Kewaneh

Where are we?
Joined
Jul 7, 2008
Messages
28
Location
Kerman, Fresno County, California
Bike
2006 ST1300
I believe this to be an electrical issue, so I'll post it here.

2006 with 137,500 miles.

During my evening commute a few nights ago on the first 90+ degree day of the year, the temperature gauge went full hot. It had been at three bars, but suddenly five bars with a flashing sixth. I dropped my speed (without a gear change) and after about 30 seconds, an immediate jump back to three bars. Not a gradual change like the thermostat sticking closed and slowly opening; three bars, six bars, three bars. This happened twice during the ride home.

I pulled into the garage and it seemed normal. After about two minutes, I turned the key to check the odometer. The ambient air temp gauge said 107 (no moving air; it was reading hot). I fully expected the fans to kick on, but they didn't. I let it sit for another minute, turned the key, no fans.

Ideas? I don't think it's the thermostat, but it might be. Fan switch? Engine temperature gauge? Main computer? I'm at a loss.
 
Does the fan move freely? Might have something stuck in there. Check the fuse I don't remember which fuse is for the fan...
 
Not sure on that one... relays can fail or they can become corroded and have intermittent failures... I was thinking that pic was were the fan fuse was - my bad - check the fuses 1st...

Then, check if the fan moves freely.. .then the relay.. that should narrow down or eliminate some obvious things.

240468
 
I do not know the science behind how the coolant temperature sensor works but when it is cold the resistance of the sensor is high, and when it goes to full hot - 6 bars - the resistance is low as in fully grounded to battery negative. A temperature gauge that swings wildly like you describe is signaling a sensor or wiring fault and not a cooling system fault. It could be the sensor itself or the wire connection to it. I recently had to replace the ECT sensor in an older car of mine as it would occasionally show fully overheated right after starting the car when I knew it was not capable of a high coolant temperature. The ST1300 service manual corroborates this. To test the gauge you remove the connector to the wire harness and ground the wires. The gauge should show full hot. If it does, the sensor is bad and grounding internally.
 
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The fans are moving freely. That's good.

I couldn't find a bad fuse, but I'm thinking it's probably not a fuse as this is seeming to be an intermittent issue, where fuses are all or nothing.

Onto the temperature sensor and the relay(s)...
 
Losing the ground 21 through corrosion or disconnection would cause the instrument gauge to never come off zero bars, full cold. If you disconnect the wire connector to part 22 and ground them to the frame or engine and the gauge then shows 6 bars - full hot - the coolant temp sensor is faulting.
 
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