OVER HEATING LIGHT 1987 K75

[jjconeill]

so just fixed my k75 87 bad ground now its overheating, has enough fluid fan seems to run than seems to cut in and out overheating light comes on and off with how fast or how high the rpm is. so sensor relay fan what else could it be? only 65f here in Chicago area, will be a problem when it's 80f
There is fluid in the overflow, I took the radiator cap off and it was full to the top, I only recently purchased the bike so I do not know the age of the fluid, I know that the ground wires under the tank have a striped thread on the bolt so I will have to tighten that, it does seem to be actually getting very hot touching the engine head and it's quite hot to the touch, and the fan is coming on I can hear it when I come to a stop, so what to do, fix ground, look in to water pump I have no knowledge as it is a new bike for me, the fan should not be on when it is 65f so fan should be good relay should be good sensor should be good, so check water pump, thanks for the help, I do love the k75 just wish it would stop not running.

[The Mighty Gryphon]

OK,first, let's get some common ground here.

The engine makes heat and the cooling system gets rid of that heat.  To get rid of the heat you need a pump to circulate the coolant from the engine to the radiator.  The radiator has to be filled with coolant to the top, and then you need air flowing through the fins of the radiator. 

You need to know that these engines run hot, too hot to touch.  To be exact, someplace around 190 degrees F.   The fan comes on about 215 degrees.   When the bike isn't moving, even in cool weather, there will not be enough air flow to keep the engine from getting hotter and turning on the fan.  When things are working properly the fan will cool things down enough to shut off, whereupon the engine will get hot again and start the fan. 

I was out in my garage today balancing the throttle bodies on my K75RT and even though it's 50 degrees, the fan kept coming on and shutting off.  It's a normal part of the operation.

Now to your bike.  A new bike should always have all the fluids changed before use.  Oil, brake fluid, and coolant.  Get a gallon of long life antifreeze, a couple gallons of distilled water, and a bottle of radiator flush.

Drain the cooling system by pulling the plug on the water pump.  Refill with distilled water and the radiator flush and run the engine for 15-20 minutes.  Drain the water and the system flush and pull a hose off and look inside to see if there are any mineral deposits remaining in the hose.  If there are, do another flush with fresh distilled water and radiator flush.  I had a bike where I had to flush it three times, the last time with white vinegar to get all the minerals out.

When it's all clean, make a mix of 40% antifreeze and 60% distilled water and refill the system.  Fill slowly, squeezing the hose on the right side of the engine gently to force air bubbles out. 

Look at the fins of the radiator.  Are they full of dirt, bugs and leaves?  Flush the fins out.  If they are packed up real well, you may have to pull the radiator out to do a good job of cleaning.  Get the fins clean before refilling.  If you have to pull the radiator you're going to spill all the antifreeze and refill. 

If you do the flush, clean the fins and refill with the proper mix of coolant you'll have your cooling system operating at maximum efficiency which it will need for those hot summer days in Illinois. 

There is still the possibility that the water pump is not working properly, but that is something for someone with more knowledge than myself to chime in on.

[Laitch]

I don't have more knowledge than Gryph but I'll make a couple of observations anyway.

After any purchase of a used bike, the oil, oil filter and coolant should be changed, regardless of what the previous owner has claimed. Here are a couple of things to check.

First, see if the fan is blowing air at the radiator, or pulling air through it.If it is pulling air through it, it's ok. If it's blowing air at it, swap its connecting wires.

Second, remove the thermostat and check that it's opening at approximately 185ºF. You do that by putting it in a pan of water with a thermometer that reads up to 200ºF or more. Attach a piece of wire to it so you can pull it from the pot for inspection. The thermostat could be stuck partially open or completely closed, preventing coolant from circulating effectively.

[jakgieger]

+1 on the points above.  My bike is a "cool" bike.  Fan seldom runs unless parked and running or sitting in traffic.  When my fan runs, it cycles relatively quickly.  This is an indication of a system cooling properly.  When the fan runs for an extended time, restriction of air or water flow is indicated.  Thus, I did the fan over-ride to keep my fan free. 

1.  clean radiator (you can use a flashlight to verify restriction in the fins0, change coolant and flush
2.  check for deposits and check thermostat if system appears pristine
3.  check fan, should warm feel air on your legs

[jjconeill]

Thanks that all sounds what I need to do, will drain system and clean, check thermostat as I believe will turn out to be the problem. Saturday. will replace the solution and find the solution also. I have a half gallon of Acura fluid from my car. I do not know anything about this as I have never changed radiator fluid in my life. a lot of VW and Yamaha air cooled vehicle's

[jjconeill]

just saw a video where a man changed his radiator fan, but he took the thermostat out, do I need a thermostat? I will not at anytime in the near future ride in cold weather, so why would I kneed one. Just a thought. Thanks for any reply.

[Laitch]

just saw a video where a man changed his radiator fan, but he took the thermostat out, do I need a thermostat?

Could you please supply a link to the video?

Your K needs a thermostat. The thermostat helps the engine to warm up then it helps to keep the engine at its optimal running temperature regardless of the temperature in which you are riding. You should have a manual to help you with procedures like this but there are several threads here to help you, too, in addition to the guidance Gryph has provided. You can download a workshop manual for your bike from the Technical Library here.

[The Mighty Gryphon]

As Laitch said, you need the thermostat to control engine temperature. 

The engine is designed to run at a certain temperature.  At that temperature the thermal expansion of the parts makes them all fit together properly.  Running without the thermostat will not allow the engine to get to this temperature. 

As a result, you'll be wearing out your engine faster, not to mention using more fuel because the engine control unit will be running a rich mixture until it senses the proper operating temperature. 

[mobydick]

I added an orange led light to my dash, where the right speaker was.  It lights when the fan comes on.

last year, first year with the K75C, I was insecure as to when it was hot and if it was cooling well and felt confident when my leg was cooking....   At least I knew why....  LOL

[jjconeill]

well nice in Chicago today, played a round of Disc Golf. then home and drained the cooling solution, put the thermostat in some hot water and it did open but not as much as I would think, guessing about one quarter to three eights of an inch, thinking that's not enough, especially after seeing the drawing that was shown with open and closed. So going to order a new thermostat and test the two together. was a bit concerned that there was some small strands of rubber on the thermostat, and the gasket on the radiator cap was not in good shape. thanks for all the help. will reply with my findings later.

[Laitch]

. . . put the thermostat in some hot water and it did open but not as much as I would think, guessing about one quarter to three eights of an inch, thinking that's not enough, especially after seeing the drawing that was shown with open and closed.

The drawing would only be accurate for that type of interpretation if it was drawn to scale but it isn't drawn to scale. It's drawn to show the difference—not necessarily the distance—between open and closed.

¼" to ⅜" should be plenty of room for effective temperature control if your thermostat is OEM. Find that out. As the disc end opens, the foot end closes the bypass. There's limited amount of room for that to occur effectively. The cap might be your problem.

The only way we'll learn which of these might be the problem is if you first install only one of the components then run the bike until it typically displays overheating symptoms. If that component doesn't fix it then install the other.

Do that and we might all benefit. Watch this and look at the open gaps of the thermostats. Begin at 10:28 if you don't want to learn too much. :giggles

[mobydick]

Oh, forgot to mention....  My handiest tool is my laser temperature probe..  I test the temperature first but carry it with me after any coolant, thermostat, filter, fuel injector etc. change.  Just point and shoot.  Presto  instant, accurate temperature with a laser. :clap: 

Now you can check the temperature at any point of your cooling system.   Hot side and cool side of the thermostat, fan motor temperature while running and exhaust temperature (air-fuel mixture differences between cylinders, burnt valves, compression probs)  etc.

Not to mention the uses on other vehicles you own... 

$20.00 approx, maybe the best money you ever spent.
have fun
MD

[jjconeill]

great information, thanks so much. will look into your suggestions and reply.