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First time posting long time rider. I have a 1986 TRX350 with a bad oil temp sensor. I recently tried to order the direct replacement but it is discontinued. Several on line honda parts suppliers say I can use the same temp sensor as my 2006 TRX500 has. It only has 1 wire on the 2006 unit. Can the sensor be used on the older TRX350 machine? If so how should it be hooked up??
 

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First time posting long time rider. I have a 1986 TRX350 with a bad oil temp sensor. I recently tried to order the direct replacement but it is discontinued. Several on line honda parts suppliers say I can use the same temp sensor as my 2006 TRX500 has. It only has 1 wire on the 2006 unit. Can the sensor be used on the older TRX350 machine? If so how should it be hooked up??
The two sensor wires complete the fan control circuit. the sensor might work but then how will the fan know to kick on?
 

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I figured i would have to ground the other wire to complete the circuit. Since the OEM parts are no longer available and I purchase a used one on EBAY that was no good I typed into a search for a suitable substitute and this popped up. Has anyone be able to make this work?
 

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Goober,
is anyone else dealing with this problem? Who would know an alternate method of repair for this situation?
Thanks,
 

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Goober,
is anyone else dealing with this problem? Who would know an alternate method of repair for this situation?
Thanks,
Hi matt
I haven鈥檛 figured that one out. However, you can leave the sensor in, unplug it, and wire the harness leads to a switch鈥搚our fan should run when you connect those two wires. Your quad will run also. The oil light will come on tho and stay on as long as the switch is on.

I bought a used case cover that had one in it鈥揑 really need to test it in oil because the boiling water trick won鈥檛 go beyond 211F.

I didn鈥檛 see the link you posted

A couple years worth of TRX250 used the same 2 wire sensor.

Don鈥檛 throw away the bad one!! There鈥檚 something in the works.
 

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Thanks Goober. I'll stand fast till I hear or see something. Have another problem now. The fuel pump doesn't run. Have to run it with the choke on to get it to move. will be working on it this weekend. Cheers!
 

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Thanks Goober. I'll stand fast till I hear or see something. Have another problem now. The fuel pump doesn't run. Have to run it with the choke on to get it to move. will be working on it this weekend. Cheers!
What鈥檚 wrong with oil temp sensor anyway?

You can wire the blue fan wire to a waterproof switch and power it from the accessory circuit. That way before it gets too hot you can turn on the fan.

Those fuel pumps have some age on them as do the petcocks. I have a fuel pump that buzzed the whole time the quad was running鈥攄iaphragm must have hole in it and wasn鈥檛 holding pressure. I bought an OEM replacement it was $150 but i buy OEM when i can-especially for this quad.

Do the flow test as described to see if it鈥檚 initially putting out enough flow. If not could be pump, petcock or blockage in tank line. If it starts out good and slows after then maybe you isolated the pump.
 

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if a oem fuel pump is still being sold by honda ?..BUY IT !. yes..they are high dollar, but !, you wont be left stranded if you buy a stupid china knock-off fuel pump from amazon or ebay that sells for about 20 bucks !. buy oem from honda !.
 

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if a oem fuel pump is still being sold by honda ?..BUY IT !. yes..they are high dollar, but !, you wont be left stranded if you buy a stupid china knock-off fuel pump from amazon or ebay that sells for about 20 bucks !. buy oem from honda !.
Here鈥檚 a good price for new genuine
 

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if a oem fuel pump is still being sold by honda ?..BUY IT !. yes..they are high dollar, but !, you wont be left stranded if you buy a stupid china knock-off fuel pump from amazon or ebay that sells for about 20 bucks !. buy oem from honda !.
Here鈥檚 a good price for new genuine
and here is the reason I don't order parts like these from ebay ----> https://www.partzilla.com/catalog/honda/atv/1989/trx350d-a/fuel-tank . $ 131.00 !!!
 

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seeing how those pumps used to run about 160-170 ?, I jumped on one from partzilla !. always best to have a spare !!!. I had to grab some front cv joint boots for my '88 trx300fw ( that I have not touched in over a month ! )..lol.
 

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Don鈥檛 throw away the bad one!! There鈥檚 something in the works.
Got an idea for a better FCU Goober? You might like this cheap lil' bugger... The Littelfuse PS103J2 interchangeable thermistor stocked at mouser.com is the one I chose for my DIY Honda FCU oil temp sensors. They are a pretty close match for stock Honda sensors as well, measuring 10,000 ohms at 25 C (77 F). Attached are the resistance/temp tables spreadsheet (saved as a PDF for posting here) and the datasheet PDF... in case you're interested.

:)
 

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Thanks @retro i bought a used sensor off a TRX250 should be here next week. I want to clean it up and test it using the hot oil technique; fix it maybe?

What can you tell me about the construction of the sensor? Can i dig out a bad thermistor from the sensor and replace it?

I鈥檇 have to replace it with a unit that loses resistivity (closes the circuit) at/just below a selected temp (to kick on the fan).
 

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The brass oil temp sensor body can be gutted using two appropriate size drill bits chucked up in a drill press to remove all of the internals. The OEM Honda sensors are easy to gut out completely and it takes just a few minutes to gut them. See this post for a couple pics:

https://www.hondaatvforums.net/forums/builds-projects-diy/128168-diy-cooling-fan-gizmo-2.html#post1282230

The oil temp sensor itself can not be used to activate a fan relay or close a power transistor because it is a signaling circuit device only... that thermie cannot handle any more than a few milliamps of current flowing through it. So it requires a voltage comparator circuit of some sort to control and activate a relay, or to bias a high current power transistor to operate the cooling fan.

You could probably buy a cheap china 2-channel voltage comparator board on ebay.... then replace the two chintzy onboard relays with quality major brand parts, balance/calibrate the two circuits using two 10k ohms potentiometers (or fixed value resistors) and you'd have the same functionality as an OEM FCU... one channel for the cooling fan motor and the other channel to turn on the overtemp warning light on the dash.

See this video for additional insight into utilizing those concepts:

 

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In the post above I mentioned that those Littelfuse PS103J2 thermies are interchangeable spec'd. What that means is each thermistor is guaranteed to perform within .1 degree C accuracy across its resistance vs temp range. In other words, you could buy 10,000 of them for instance, mass produce your own Honda temp sensors... and each one of your mass produced sensors would perform identically to any another provided they were made using the same hookup wire diameter with the same wire lengths. So if a sensor ever failed a new one of the same design specs could be swapped in without recalibrating your FCU.
 
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