Overheating?

After the bike has warmed up, the temp light on my K75 comes on and stays on, even at speed. Is this a faulty temp sensor, or can the bike actually be overheating at 40+ mph?
Over the past year I've replaced the thermostat, fan relay and fan relay.
Thanks,
Mike

How is your coolant level??

The way that I found that my fan was bad in my old "C" was when I got stuck in traffic and the hot light came on. You can check you fan by trying to turn it manually with something long like a pencil. If you can't get the fan blades to turn easily then it's probably no good.


You can also let your bike idle in place for about 15 min or so and listen for the fan to come on.

mgalie said:

After the bike has warmed up, the temp light on my K75 comes on and stays on, even at speed. Is this a faulty temp sensor, or can the bike actually be overheating at 40+ mph?
Over the past year I've replaced the thermostat, fan relay and fan relay.
Thanks,
Mike

Click to expand...

This is the "shoot the messenger" syndrome, where we'd rather believe the warning is wrong then something is really wrong.

I'd suggest reading: http://forums.bmwmoa.org/showthread.php?p=466686&posted=1#post466686 - then decide if you want to continue riding with an overheat light showing.

We can't diagnose it over the Interwebz given the info you've provided. It would be helpful to have a good thermometer handy to measure the radiator temps, and some info as to if the fan is coming on with the light (it should have come on BEFORE the light) would also be useful.

Sorry about the limited info, guys.

This morning I checked all of the hose clamps and let the bike idle until the temp light came on. It took about 12 minutes for the light to come on in the 80 degree air. One thing of note, when the fan kicked on it was blowing noticeably COOL air.

Also, coolant level is fine; it seems to be trickling in and out of the reservoir just fine and it is not overfilled.

As to the thermometer and getting actual data, I only have the kind you use to stick the turkey with. I sort of doubt its accuracy in this application, so I didn't even bother using it. What kind of thermometer would you suggest using?

mgalie said:

Sorry about the limited info, guys.

This morning I checked all of the hose clamps and let the bike idle until the temp light came on. It took about 12 minutes for the light to come on in the 80 degree air. One thing of note, when the fan kicked on it was blowing noticeably COOL air.

Also, coolant level is fine; it seems to be trickling in and out of the reservoir just fine and it is not overfilled.

As to the thermometer and getting actual data, I only have the kind you use to stick the turkey with. I sort of doubt its accuracy in this application, so I didn't even bother using it. What kind of thermometer would you suggest using?

Click to expand...

Have you touched the radiator? If the fan was blowing cool air than the coolant in the radiator might not be circulating properly. Is there a thermostat in the K bikes? Your radiator could also be empty. When was the last time the coolant was flushed?

I changed all of the fluids last month and the radiator looked as clean as a whistle... The thermostat has also been recently replaced and all the hoses feel pressurized when the bike is hot. Even if the thermostat wasn't opening, the light should not come on at highway speed, no?

mgalie said:

I changed all of the fluids last month and the radiator looked as clean as a whistle... The thermostat has also been recently replaced and all the hoses feel pressurized when the bike is hot. Even if the thermostat wasn't opening, the light should not come on at highway speed, no?

Click to expand...

When you changed fluids, did you start the motor as you were filling the radiator?
Is the pump pumping? Without circulation it's entirely possible to have the temp high at speed.

First thing to do is recheck the coolant at the radiator cap (requires sliding tank back) to be SURE there is adequate coolant in the radiator. There might have been a month ago but it wasn't overheating a month ago. Check it again!

I didn't get the light recently but the gauge ran right at the edge of the red at highway speeds on my 1996 K1100RS.

The next day I worked on it and I think I had an air blockage somewhere. I started it up with the cap off and waited until it coolant started rolling, the fan came on, etc. I believe I saw an air bubble.

On the way back home it ran great just above the half way mark. I only added about a cup of water. when I got home I replaced the cap and thermostat as a precaution. they were probably original on the bike.

I think it is better to start it with the cap off and visably watch it and add fluid if needed. When it starts rolling, the thermostat has opened and then the fan kicks on.

I would make sure everything is working before going for the light

I put in a little less than half a liter of AF mix last night and that did the trick. Feeling pretty stupid for not reading the directions: i.e. checking the level while the bike's hot. On the other hand, it's a relief that it was such a simple fix.

I wouldn't have thought that a 15% difference in coolant would make such a HUGE (I mean really really really big!) difference in the engine's temperature regulation.
Thanks for the tips and the lesson, guys!

K75RT Overheat, piggy back previous thread

While searching for info to help with my situation, found this thread and hope to piggy back on it to gather the collected wisdom from the Forum.
The situation is the fan will not come on but it does turn freely by hand. My history and background on it are;
1. 1995 K75RT is new to me (1st bike), as of August 2009. Got it with 33,000 miles and I am at 42,000 miles now.
2. Until yesterday, all my riding has been in cool weather (35 - 75 F) and not a lot of stop and go.
3. Yesterday, 80 degrees, after a 20 minute highway ride, 2-up, got stuck in stop/go traffic and overheat light came on within 5-10 minutes. Once I got going and over 25 mph, light was out.
4. I did the static fan test this morning and it turns freely when pushed.
5. Shortly after I got it (35,000 miles) last fall, I had a local dealer change the air and fuel filter and coolant. They also replaced the water pump seal since it had a small leak down there. No idea if the fan was working before or after that work since I never hit a situation like #3.
6. A few months back, at 39,000 miles, I jumped in and did my first clutch spline, drive shaft spline lube.
7. Electrical work is my weak point - talking about resistance, ohm meters, etc and my eyes glaze over.
Given the above info, is there an obvious possibility of some connection that did not get made during the dealers or my maintenance work? I'm hoping that I can get pointed in a direction for a fix without having to do a lot of disassembly and reassembly.