Overheating issue, running out of ideas

[Generic]

This is on a 2005 Z750S

Bike was serviced and tuned in August of 2012 and I've ridden it weekly since.

Main Issue - Dash overheat light is cycling on and off even in relatively cool weather. This started in Sept. last year, at the time I thought the fan temp switch had gone out so I direct wired the fan to a switch and handled it manually. Fast forward to this year and here is what I have done:

• Replaced fan temp switch - New one works properly
• Drained, flushed and refilled coolant
• Replaced the thermostat
• "power" flushed the cooling system with the hose
• Visually inspected the water pump impeller for damage/wear
• Replaced the pressure cap
• Bled the system repeatedly

The results of all that are that it now overheats less often and cools off quicker but I'm still getting the warning light. This happens sitting at idle
or at highway speeds and of course sitting in traffic. The fan will kick on after the overheat light has come on, according to the manual the fan trigger temp is a solid 30F lower than the warning temp however.

At this point I'm thinking it is an electrical/sensor issue and it's triggering far lower than it should. The bike isn't cooking me, power seems fine, I don't think I have an overly lean cylinder or anything. I did just order a laser temp gauge so I can check each pipe for hotspots however.

Cooling system diagram



I'd love some input and feedback from you guys, thank you!

-Murdock

[Chaos]

What is the indicated coolant temp when the light pops on?

[The GECCO]

^^^
What he said. Have you confirmed via some other method that the bike is actually overheating? Could it be a false light?

[Generic]

What is the indicated coolant temp when the light pops on?

I haven't verified the temp independently, that's my next step as I'm pretty sure the sensor is off.

[Chaos]

Oh, so there isn't an actual coolant temp read out on your gauges? (sorry not familiar)

[Generic]

Oh, so there isn't an actual coolant temp read out on your gauges? (sorry not familiar)

No, sorry, that would be very nice if I had one. All I have is an LED indicator that is on at 230ish and flashes over 250F (I think, it's not called out specifically, I have to convert to resistance to come up with these numbers)

The fan comes on at 200-217F and off again once the temp drops 38-46F

[The GECCO]

I haven't verified the temp independently, that's my next step as I'm pretty sure the sensor is off.

When you get the laser temp gauge you can use that. Point it at the METAL part of the radiator neck on the side of the radiator where the water comes out of the engine. This will be the higher of the two necks, the lower neck should feed the hose that goes to the water pump, this is the cool side. Not trying to condescend, just making sure

[Generic]

When you get the laser temp gauge you can use that. Point it at the METAL part of the radiator neck on the side of the radiator where the water comes out of the engine. This will be the higher of the two necks, the lower neck should feed the hose that goes to the water pump, this is the cool side. Not trying to condescend, just making sure

So I just measure all for exhaust pipes, inner two are hotter as expected, so I don't think I'm running hot in one cylinder or anything.

After that I checked the entire coolant flow, out of the radiator, in the pump, out of the pump, in the block, collector out of the block and upper pipe to the thermostat and sensor housing followed by the outflow and the lead into the radiator.
At about 210 on the metal of the radiator at the fan temp switch the fan kicked on as expected. The coolant light was already flashing (highest warning) at this point. No other temps were over about 215. This is sitting idle in the driveway at about 85F outdoor. I'm pretty sure the temp sensor is shot at this point. I'll pick one up next week and swap.

Murdock

[The GECCO]

So I just measure all for exhaust pipes, inner two are hotter as expected, so I don't think I'm running hot in one cylinder or anything.

After that I checked the entire coolant flow, out of the radiator, in the pump, out of the pump, in the block, collector out of the block and upper pipe to the thermostat and sensor housing followed by the outflow and the lead into the radiator.
At about 210 on the metal of the radiator at the fan temp switch the fan kicked on as expected. The coolant light was already flashing (highest warning) at this point. No other temps were over about 215. This is sitting idle in the driveway at about 85F outdoor. I'm pretty sure the temp sensor is shot at this point. I'll pick one up next week and swap.

Murdock

Sounds like you're on the right track.

[Generic]

Replaced the sensor last night finally. Let it warm up at idle, fans kicked on like normal and no more temp warning light. Went out for a ride and then road in this morning, still no light. The ride home in the 90F heat will be the real test, but I think the sensor was the issue.

End the end, all the other crap probably needed to be done anyways, just annoyed it took so long to isolate.