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Kevin, Technician
Category: Small Engine
Satisfied Customers: 732
Experience:  Over 10 years as a Deere Service Tech.
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My John Deere Gator is also over heating and fan motor is

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My John Deere Gator is also over heating and fan motor is not coming on. I cannot find a filler plug by the thermostat housing. While working on it I did get fan motor to come on one time last night but it is not coming on when coolant gets hot. Coolant is steaming out of overflow holder. Air filter is reasonably clean.

Hello, my name is XXXXX XXXXX I can help you with your question.


While I'm not sure what model of gator it is you have I'm assuming that it is a 6x4, the cooling system is fairly basic. The air purge plug that you are looking for is located on top of the middle of the intake manifold. With the engine running loosen the bleeder screw until only coolant comes out and snug it back up.


The electric fan is turned on by a temperature switch (#13 in the attached diagram). Check the connection on switch and wire wires leading up to it. If you have a ohm meter the temp switch should be open when the engine is cool and closed when hot.



One other issue that we have started to see on older gators are the water pump drive gear fails. The water pump bearing will get loose causing the drive gear to ride high and strip the teeth off as the gear is plastic. If your water pump has failed you will find the radiator and hoses at the radiator are cool when the engine is over heating.


With any luck this will help you narrow down the source of your problem. If this has answered your question please hit the green "Accept" button so I get paid for helping you. If you need further assistance please reply to this message and I will be more then happy to help you out.




Customer: replied 7 years ago.
This Gator is diesel and is a 6 by 4. Serial # XXXXX I do not know year but could look to see if model # XXXXX XXXXX frame. Do you have a diagram that shows exactly where the vent plug is located. I have and operators manuel and the picture it shows looks like it is behind the thermostat. If you take off thermostat housing and fill with fluid there and the vent plug out of radiator top and fill at both of these places will that make sure the air is out of coolant system? Thanks!

My apology, I assumed it was a gas engine.


On the diesel engine there is a bypass tube leading from the thermostat back down to the water pump. It is the responsibility of the bypass tube to help force air up and out of the system. In short the diesel is supposed to be a self purging system. If you filled the engine with coolant via the thermostat housing as you described that would do a exceptional job of filling with out risk of trapped air.


I personally have not had much trouble with the water pumps on the Diesel gators but it still wouldn't be a bad idea to check the hoses to make sure the water pump is flowing coolant.


I have attached to break down of the diesel water pump just as a visual reference.


Let me know what you find.



Customer: replied 7 years ago.
I opened vent on radiator and poured in coolant until full and put in vent plug. I ran Gator long enought for engine to be hot . Both hoses (top and bottom) were hot ( or same temp.) The cooling fan never came on. Do you have diagram of where the ground wire is grounded and if I put a hot wire from external source to the red wire leading to cooling fan when engine is hot will the fan come on? Cooling fan has #1 red wire and #2 black wires going to it. And what is the best to clean contacts of wire. I used WD 40 b/c it has some pressure and is a solvent. Thank You, Mark



It sounds like your problem revolves around the cooling fan. Unfortunately I can't give you the wiring diagram due to copy right but I can help you with the wire routing.


The F2 fuse is responsible for supplying power to the cooling fan motor. The supply fuse does not supply power to any other function on the gator. The red/blue wire (this would be the wire on the machine harness) that goes to the cooling fan should be hot all the time via the F2 fuse.


The cooling on off is controlled from the ground side by the radiator core temp switch. The black wire on the cooling fan goes directly through the core temp sensor and the core temp sensor ground lead is grounded to the frame by a eyelet.


The diagram that I have for your serial number gator only shows the cooling fan to have two wires, one red and one black. The red wire goes to a red/blue wire in the main harness and the black wire goes to the black wire in the harness. You should be able to make your cooling fan run by simply grounding the black wire to the frame. If it does not run then the F2 fuse is blown. You indicated that when it is hot you can make the fan run by putting power to the red wire. This would indicate that the core temp switch is working and the fan motor is good. I'm guessing that you have a blown fuse or a broken wire.


Interesting fact, your gator is the first machine to roll off the assembly line for its model year. The 8807 gator serial number is XXXXX noted as the changer over from the early style wiring system to the late.


The fuses should be located under the drivers or passengers seats.


Keep me posted.




Customer: replied 7 years ago.
I can not get the fan to come on. The red wire is hot as I checked with volt/amp meter. I unplugged the 2 black wires . I tried to ensure the red wire is getting current with the red wire on gator and also to an external battery. I grounded the black wire that goes directly into the cooling fan to the frame and the cooling fan did not come on. So I believe that the cooling fan must not be working. I appreciate all your help and would ask if you agree with my reasoning on the cooling fan? Thank you, Mark

I would agree with your conclusion, it sounds like the fan motor itself has failed. I'm glad to hear you have gotten to the bottom of the problem.



Customer: replied 7 years ago.
Well I went back out and I got the fan motor going with red wire on and grounded the black wire to body . So the switch on the radiator must be bad. One last question. How do you take the switch out for replacement.? Thank you, Mark

The radiator core temp sensor threads into the radiator. It should be reinstalled with Teflon tape. You asked about a good wire cleaner in one of the previous posts and I forgot to answer. While I prefer John Deere Electronic contact cleaner brake and parts cleaner will also work.


Good luck,


Kevin and 2 other Small Engine Specialists are ready to help you
Customer: replied 7 years ago.
I appreciate all your help. Thank You ! God Bless You! Mark Tackett

My pleasure.



Edited by Kevin on 7/12/2010 at 10:14 PM EST