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Discussion Starter #1
I have a 1998 Yamaha Grizzly 600 YFM600FWA 4WV5-010 here with an overheating issue - the oil cooler fan is not turning on and eventually the Oil Temp red light is illuminating.



I've read a number of old posts that indicate these run hot and gave some start points. So far I have:

Tested that the actual fan works by directly connecting 12v (positive to blue wire and negative to black) to it's electrical connection plug:



It spins up and works.

I then looked at what I believe to be the oil temperature switch. The electrical connection seems fine:



I disconnected it and bridged:



The oil cooler fan started up and the oil temp red light lights up - indicating that perhaps this sensor switch is at fault?
But what I don't understand is why does the red Oil Temp light up but the fan doesn't, but then when the temperature switch sensors electrical connection is bridged both run? Is this temperature sensor switch for the fan or red Oil Temp light? I would assume that the fan should turn on well before the red Oil Temp light illuminates to indicate overheating?
 

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Look for another sensor for the light. Just a guess, I haven't done a 600 yet.
 

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Discussion Starter #4
Look for another sensor for the light. Just a guess, I haven't done a 600 yet.
Yes, I haven't noticed one on it yet. There isn't any other obvious sensors.

Having a look at the Partzilla catalogue it shows the one sensor in Electrical 1 < Yamaha ATV 1999 OEM Parts Diagram for Electrical - 1 | Partzilla.com > as part 11.
Electrical 2 < Yamaha ATV 1999 OEM Parts Diagram for Electrical - 2 | Partzilla.com > doesn't seem to show any further sensors. It does list 24 and 25 as the Circuit Break Assy and Thermo Switch Assy which I believe are related in the circuit for it but not the temperature sensor to trigger the light.
 

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I had the same problem. For me, it turned out to be a wire shorted to the chassis, causing the lamp to turn on and not the fan. I was 100% convinced that I was running hot before finding the short. In the end, I found two places where the wiring harness was failing: Near the exhaust (causing other problems), and up front just forward of the steering. There is a bundle of wires running along the top of the frame. Insulation completely rubbed off several wires.
98913
 

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Discussion Starter #6
I had the same problem. For me, it turned out to be a wire shorted to the chassis, causing the lamp to turn on and not the fan. I was 100% convinced that I was running hot before finding the short. In the end, I found two places where the wiring harness was failing: Near the exhaust (causing other problems), and up front just forward of the steering. There is a bundle of wires running along the top of the frame. Insulation completely rubbed off several wires.
Thanks. I'll go through and thoroughly examine the wiring harness to check.
Out of interest though, was your Oil Temp red light constantly coming on then? Or was it just coming on intermittently when the exposed wires moved and rubber when in use?

On the bike I have here the Oil Temp red light only comes comes on after considerable amount of use that would be sufficient for the oil temperature to be hot enough to be overheating. Around the engine area also feels very hot. If it's then shut down and allowed to cool for a while when restarted it will overheat much quicker until left for considerable time (e.g. overnight). So I think this bike is genuinely overheating but the fan isn't coming on.
 

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Discussion Starter #7
Having studied both the parts diagrams and electrical wiring diagram (both linked above), I don't understand how the Oil Temp and fan are separately triggered - the fan should be triggered earlier than the Oil Temp red light as that should only come on when the oil is overheating and the fan has been unable to sufficiently cool it.
There seems to be only one Thermo Unit (21) which would presumably only set one off. But perhaps the Fan Motor Control Unit (20) that it goes to senses the different resistances and can distinguish the lower point of when to turn the fan on and the overheating point when the Oil Temp red light needs to be illuminated.

For the Fan Motor Relay (18), it looks to have two triggers before it powers the Fan Motor (19).
The first is the Br wire (presumably relay pin 86) looks to have a live 12v+ positive feed that is enabled by the Main Switch (2) - presumably an Accessories or Ignition - this would stop the fan from running when the bike is shut down/off.
The second is negatively triggered by the W wire (from presumably relay pin 85) going to ground (GND) through the Fan Motor Control Unit (20) B wire (GND). This allows the Fan Control Unit (20) to control when it wants the Fan Motor (19) to run by completing the circuit to ground, or breaking it, to start or stop the motor.

The other two wires on the Fan Motor Relay (18) are:
R/W wire (presumably relay pin 30) looks to have a live 12v+ positive feed that is enabled by the Main Switch (2) - presumably an Accessories or Ignition - it actually connects back to the Br wire (that feeds what is presumed to be relay pin 85). The key difference here is that it goes through a Circuit Breaker Fan Motor (17) before the Fan Motor Relay (18) - likely as a protection mechanism to avoid overloading in the event of a failure etc. as I imagine the fans location makes it easy to become damaged or blocked up and fail.
L (presumably relay pin 87) connects to the Fan Motor (19) and provides it with power when the relay has been triggered to activate.

Therefore, since this bike is just used for low tempo, low speed maintenance tasks (weed spray, horse feed delivery, horse poo collection, etc), which don't promote much air flow over the oil cooler radiator, I plan to rewire it so that the fan is constantly running with the bike ignition. To achieve this I think it's simply a matter of adjusting the Fan Motor Relay (18) W wire (from presumably relay pin 85) to go directly to a ground earth. Since the Fan Motor Relay (18) would then have a constant ground earth connection on the W wire (from presumably relay pin 85) the relay should the activated and therefore power the Fan Motor (19) when ever the first trigger on the positive Br wire (presumably relay pin 86) is enabled by the Main Switch (2) - i.e. when the bikes key is turned to On it should start. The second trigger on W wire to the Fan Motor Control Unit (20) is removed - so the Fan Motor Control Unit (20) no longer has control of the Fan Motor Relay (18).

I'm no auto electrician so very interested in anyones opinions/comments if I've misinterpreted any of the above...
 

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Discussion Starter #8
I tested out my above outlined theory this evening. It all checked out so I carried out the modification and it has worked perfectly - the fan now comes on and off with the bikes ignition key. It’ll be constantly running with the bike but I don’t think this will be an over cooling issue as these bikes generally run hot and this particular one is used for a lot of low speed work which doesn’t promote good air flow over the oil cooler radiator.

it also means that should the fan motor relay ever fail it could easily be replaced with a generic automotive style relay if the proper Yamaha product was unavailable or overpriced.

my modification uses all the other components except for the thermo switch and control unit. I suspect in my case I have a faulty fan controller module which is not earthing out the relay when it should to trigger the fan on to run. It could otherwise be a thermo sensor issue but I believe that this same unit also triggers the Oil Temp overheating red light, which seems to be working, so I’m presuming it’s possibly still ok. While I’ve not had a thoroughlook at the wiring looms I suspect that there is no run through short occurring as that should trigger the circuit breaker and/or blow the fuse.
 

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Out of interest though, was your Oil Temp red light constantly coming on then? Or was it just coming on intermittently when the exposed wires moved and rubber when in use?
That is what was odd about my situation. The light would only turn on (steady) while riding up a long hill. It would turn off when going down hill. I spent a lot of effort in troubleshooting a hot engine problem, but in the end it was the harness. I'm thinking the wire was just loose enough to short out only when pointing up hill.

Does not sound like it is related to your problem.

Yes the fan motor control unit will turn the fan on at a lower temperature than the high temperature indicator lamp.

On page 8-38, they have a test for the thermo unit, and I used this information to test the motor control unit. There are two temperatures listed. 302 F and 428 F. I assumed that 302F (less than around 330 Ohms) is when the fan should turn on, and 428F (less than around 230 Ohms) is when the high temperature lamp should turn on. I used this information and a variable resistor to test the motor control unit. In the old days, you could go to radio shack and get resistors. Not sure if they do that any more. Not sure if radio shack is still in business.

I disconnected it and bridged:

The oil cooler fan started up and the oil temp red light lights up - indicating that perhaps this sensor switch is at fault?

But what I don't understand is why does the red Oil Temp light up but the fan doesn't, but then when the temperature switch sensors electrical connection is bridged both run? Is this temperature sensor switch for the fan or red Oil Temp light? I would assume that the fan should turn on well before the red Oil Temp light illuminates to indicate overheating?
I think this is an important clue. The lower the resistance (bridged = 0 Ohm), the hotter the fan control unit thinks the oil is so it turns everything on. The only question: is the problem the thermo unit (not sending correct resistance), or the control unit (not detecting correct resistance)? If you have a Voltmeter (with Ohmmeter function) and some resistors you can test the control unit. Thermo unit test needs a hot oil bath and a thermometer to test.
 

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Discussion Starter #10
That is what was odd about my situation. The light would only turn on (steady) while riding up a long hill. It would turn off when going down hill. I spent a lot of effort in troubleshooting a hot engine problem, but in the end it was the harness. I'm thinking the wire was just loose enough to short out only when pointing up hill.

Does not sound like it is related to your problem.
Well, I think I have to eat my words. I did the fan mod two nights ago but didn't start the bike or test ride it was it was too dark, too cold (like 40*F outside) and a bit too late to make noise when the family and neighbours were in bed. Yesterday afternoon after work I kicked it over and took it for a test ride - the fan ran as soon as I put the key in the 'On' position and kept running the entire time. Except, about the same point on the ride, when the bike was warmed up the Oil Temp red light comes on!!!

This time, instead of just shutting the bike down immediately, I first, while the engine is still running, put the bike transmission from H into Neutral and a start noise starts up. The noise is the starter motor engaging and running - even though the engine was still on running away the starter motor is kicking in. So that red Oil Temp light isn't being triggered on by temperature of the oil, in this case it's coming on because something is telling the starter motor to run (and for what ever reason it illuminates when the bike is starting).

It's strange though as the first occurrence always takes some time - 10 or more minutes, but after that it reoccurs every 1 to 2 minutes or so. How long it takes to stop also varies - sometimes quickly when the bike is shut down but other times 30 seconds or a minute - so if you turn the bike back on it will self start.

I think perhaps your right that there may be some wire rub on the loom causing this. It's fairings off this afternoon now.
 

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Discussion Starter #11 (Edited)
I cannot see anything in the starter system that connects the strarting system to the Oil Temp red lamp.



Looking through this it seems you need all of the following to occur in order for the starter motor to engage:

Starter relay (9) triggered through presumably relay pin 85 being grounded by:
Starter switch (41) pushed to trigger the starer relay (9)
Engine stop switch (40) in On position to enable the Starter switch (41)
Main Switch (2) in On position to enable the Engine stop switch (40)

Concurrently the starter relay (9) needs to be triggered through presumably relay pin 86 being fed a live 12v+ by:
Activation of the Starter circuit cut-off relay (12) which outputs presumably pin 87 to the starter relay (9)
Starter circuit cut-off relay (12) presumably relay pin 85 trigger is activated by the CDI unit (13) Relay output

The Starter circuit cut-off relay (12) receives it's relay pin 30 and 86 12v positive when the Main Switch (2) in On position through the Main fuse (3) and connection to the Positive lead (6) of the Battery (7).

CDI unit (13) is connected to
Neutral switch (31) via Br to N
Rear brake switch (16) via G/Y to BRK and B to GND - I'm not sure exactly how this works but presumably this circuit needs to be closed (by applying the rear brake) which internally to the CDI unit (13) tells it its safe to start up.
via B/W wire to STP on CDI Unit (13) the Main switch (2) and Engine stop switch (40).

Out of that list I think it's most likely that the starter switch (41) would be linked to the fault as this is on the negative trigger (presumably relay pin 85) which completes the circuit by grounding. As nothing is pushing it at the time when the starter motor is engaging it either means an internal failure of this switch causing an internal closed circuit while not being pushed - or, more likely, it's wire (R/W) from it to the starter relay (9) is at fault (I think this wire goes to the equivalent of relay pin 85 on the starter motor relay).

The starter switch (41) is on the handlebars at the front of the bike, but I believe that the starter motor relay (9) is at the front of the engine colocated as part of the starter motor (rather than at the rear which is likely where the Starter circuit cut-off relay (12) is) - which shortens the likely length of wire that may have been damaged/rubbed through to cause this. Anywhere along it that it is rubbed through and earths out on the bike would be sufficient to complete the circuit causing the starter motor to run if all other parameters (those listed above) were also met.

What is interesting though is that the rear brake switch (16) doesn't seem to be effecting this as it's not applied when the bikes trying to self start...
 

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I'll have to look closer at the circuit diagram, but as I recall, the oil light will turn on when the starter button is pressed. If you want to test this out, remove (disconnect) diode 23 from the circuit. If the lamp no longer turns on, then you are correct in thinking that there is a problem with the starter circuit.
 

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Discussion Starter #13
All sorted now - you were right Amadues - wire rub shorting out on the chassis. Right side above the exhaust.

After removing the plastics, first I tested the Starter switch (41) and Engine stop switch (40) - all checked out fine.




On a side note, the cooling systems circuit breaker seems to also be collocated in this area:



The Starter relay (9) is located at the rear of the bike next to the other three relays (one being the Fan Motor Relay (18) [right-most white relay] and one presumably being the Starter circuit cut-off relay (12)). The Starter relay (9) is easily identifiable by the larger sized cables and is the different looking one on the right side:



This means that the R/W wire from the Starter switch (41) to the Starter relay (9) runs the length of the bike and has ample length for failure to occur. Thankfully in this case it was easy to spot once the seat was removed - above the chassis frame on the right side where the wiring loom crosses over - likely helped by the hot temperature of the exhaust below it:




I tested this as the fault by applying an earth wire to the exposed copper. The starter motor and red Oil Temp light came on immediately. It's repaired and covered up now.
 

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Good that you caught it early. I ended up smoking my harness (on the trail) and had to replace it all. Fun times......
 
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