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Retro's oil temp mod question

4K views 38 replies 8 participants last post by  marlinman 
#1 ·
I started a new thread cause I wondered if anyone else might chime in on this issue. This is for the '86 and other years that apply, TRX oil temp sensor, not kicking the fan on till about 300 deg.

Was talking with a neighbor this evening about this and we got to wondering if an external temp sensor could be mounted somewhere to kick the fan on a bit earlier?

I am not too familiar with things like that, but it sounds reasonable. To me anyway, not like that means a whole lot.
 
#2 ·
I had forgotten but... shadetree mentioned way back that he had found a solution for one of his motorcycles by buying a sensor (from an auto parts store I think?) that was made for a different motor/application and simply swapped the new sensor in. You might want to look into that option... find some that fit into the side cover (or use an adapter) and from there its just a matter of putting a sensor in there having less resistance than stock. It may involve some trial & error testing to get one that kicks the fan on where you want it to, but once you learned which sensor works the best everyone could benefit. I'd do it that way myself if I knew which sensor to buy... I'm a tightwad though.
 
#3 ·
Have you checked the temp just to be sure? I used an infra red temp sensor/gun when I tested mine.
It's a shame nobody makes a sensor that fits in between the cooling find on the head, I realise the temp sensor would have to be lower operating temperature but I for one would certainly consider buying one.
I have my fan running through a switch and Its always on your mind, a little distracting I find if I'm honest.
 
#4 ·
Hi: Just do it the simple way -- wire in a toggle switch to turn the fan on and off at will.
The sensor still stays there to turn the fan on also if you don't turn the the toggle switch on. See diagram.
 

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#5 ·
Mine didn't work at all, hence wiring in the switch. At the time I was wanting to use the ATV, it's undergoing surgery at the moment and she a wiring harness swap so I may well get the fan working on the sensor and also through a switch.
 
#6 · (Edited)
the problem with installing a switch to turn the fan on ?, some ppl forget the fan is on ?, then they have a dead battery !..lol. kinda like some switch the '' kill '' switch off, and forget to put it back in the middle ?, or..turn the fuel off, take off, and it dies..and they don't know why ?...trust me..WE ALL DO STUPID STUFF ..OR WE WILL !..LMFAO.
 
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#9 ·
With sensor bypass switch installed -- when you turn the key switch off the fan goes off -- Yes STUPID STUFF if you leave key on without the bike running -- sure the battery will go dead -- so installing the bypass switch is not STUPID STUFF.
 
#7 ·
I've done the fuel tap trick so many times shady! Haha. They always seem to die half way up a good hill climb or just as you enter a good mud hole to ha!
My fan is quite loud so I usually hear it, not forgotten it as yet.
 
#8 ·
lmao, I hear ya..they ALWAYS DIE IN THE WORST PLACE !..LMFAOOO, I can attest to this, was moving my jet ski around my yard/drive way one day, using my '03 trx450fm that I just finished, had it out in the street backing it up, atv died..wth ????..crap..after a few seconds, dawned on me, fuel was shut off !..lmfaoooooo.
 
#11 · (Edited)
Some like myself just want to switch the fan on before the sensor kicks in. You can wire the switch to the sensor or wire the switch to the green wire on the Fan. The sensor changes resistance as the engine heats up -- the resistance of the sensor goes lower to a point where there fan starts that resistance is wide gap not just a true turn on point for the Fan to start.
Riding a ATV real slow for hours at a time when hunting I prefer to have the Fan running at all times -- also pulling large game animals out of the woods I prefer to have the Fan running at all times.
Some people run there ATV's a long way from home -- leave from the house by bike and bike (100+ Km), not just just a few Km around there house. Just another safety feature if the sensor fails.
 
#12 · (Edited)
I agree with Melatv. A manual switch, even if its never needed, or never used regularly by the operator, is a great option to have on any fan equipped bike.

As they say, an ounce of prevention is worth a pound of cure... that certainly applies to overheating your motor oil. Once a certain high temperature threshold is reached, every motor oil is permanently junk and must be changed out immediately. Those high temp thresholds for motor oils are much lower than many think!

When the operator knows the bike is going to be put to some slow or hard work, they can simply turn the fan on to prevent any potential excessive heat saturation issue from gaining legs. If the fan motor, or the fan control unit ever fail, the operator may be alerted to that problem before damage is done too.

Its got to be done right like though, like Melatv explained with his drawing. It should be a professionally built installation plugging directly into the existing harness plugs, ONLY. Expect no mercy if you're the hacking, cutting, splicing, taping, kind of guy around vehicle wiring harnesses!

I am going to implement both an adjustable fan control kick on AND the manual switch features into mine. I'll also add a tiny indicator light somewhere that glows while the fan is running. I'm convinced my bike will benefit.

Thanks for this thread!
 
#13 ·
I have my on/off switch wired to a hot wire that is turned on/off with the key...it also connects to a 15A fuse in the rear trunk of the bike. I got tired of trying to find a good working fan relay unit so now I can just run the fan whenever and as much as I want to :icon_ banana:
 
#15 ·
@PatrickB,

If you ever get a good fan control unit you can add a relay between it and the fan motor to help keep the new controller alive. The early (86 & 87) fan controllers had no overloading protection built in, so they can fail if the fan ever stops turning (or drags) for any reason. A stick in the blades for a brief moment is all it takes sometimes. 88 & later they added self-protection and could shut power down going to the fan motor, rather than smoke the output power transistor in the controller.

@vwmg,

Yeah... in the FSM the minimum specified temp for the cooling fan to kick on is 308 degrees fahrenheit. Most motor oils are already permanently junk by the time that fan kicks on.
 
#16 ·
I don't have my service manual sitting in front of me ?, but I don't think it's 308 deg's ?, a little over 200 something ?, i'll have to look it up when and if I remember ?!..lol.
 
#17 ·
I just want to toss this in, and leave it be :). do I think a manual over ride switch to turn the fan on is a bad thing ?..NO !. what I do believe , is if the sensors and all is working like it was when it left the factory ?, then there is no reason to start adding all these after market parts on there just because no one wants to replace that 60 dollar ( give or take ) sensor to operate the oil temp sensor to get the fan to turn on, that's all I am trying to point out :). I have my '89 trx350D foreman complete stock except the tires ?, and a winch, and not once have I had a oil temp fan issue sense I starting riding it ?. to each their own :).
 
#18 ·
I don't have my service manual sitting in front of me ?, but I don't think it's 308 deg's ?, a little over 200 something ?, i'll have to look it up when and if I remember ?!..lol.
Ya, I was wrong about the kick on temp. I don't know where I got the 308 figure from... but thanks for correcting me shadetree! The FSM states:

"When oil temperature goes over 110-130 C (270-306 F) sensed by the oil temperature sensor, the fan motor operates through the control unit.
When oil temperature goes over 170-190 C (378-414 F) the oil temperature indicator comes on through the control unit and alerts that the oil temperature is rising critically high"



I just want to toss this in, and leave it be :). do I think a manual over ride switch to turn the fan on is a bad thing ?..NO !. what I do believe , is if the sensors and all is working like it was when it left the factory ?, then there is no reason to start adding all these after market parts on there just because no one wants to replace that 60 dollar ( give or take ) sensor to operate the oil temp sensor to get the fan to turn on, that's all I am trying to point out :). I have my '89 trx350D foreman complete stock except the tires ?, and a winch, and not once have I had a oil temp fan issue sense I starting riding it ?. to each their own :).
I agree that we disagree. :) I believe that if the oil temp sensor and all is working as it was designed when it left the factory, that the factory engineers screwed up big time and never took the opportunity to correct their error in subsequent years.

Why? Because most (if not all) motor oils available in 1986 thru 1989 could not survive the minimum 270 degree temp required to kick the fan on. The spec ranges from 270 up to 306 degrees and is still considered normal by Honda! And yes, Honda branded oil was one of those incapable oils as well, that could not survive those extreme high temps. The same oil that was put in the crankcase when buyers took them home from their dealer was overheated and was completely junk when that cooling fan kicked on for the very first time.

I doubt if the Honda recommended motor oil sold today will survive those extreme temps either.

Only a very few expensive synthetics are likely to survive several heat saturation cycles over the 270 - 306 degrees range, for the life expectancy of an oil change. None of those high dollar synthetic oils are capable of surviving the 378-414 degrees temps required to kick on the warning light.

The point I'm making is that Honda screwed it all up bigger than Dallas. It may have been one of their biggest blunders ever. OEM parts can't ever fix it. So leaving it stock is not ever gonna be a safe option for anyone who puts their machine to work. Its gonna get fixed right this time.
 

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#22 ·
So since the temp sensor measures around 10K (10.7K on mine) at room temp, does anyone know what it measures when it gets hot? I am wondering if one couldn't just add a resistor, fixed or adjustable, in line with the sensor to fool the control unit?

Wouldn't that cause it to kick on sooner?
 
#24 · (Edited)
@marlinman,

Yep, that idea was tested HERE although I'm sure its not the first time someone did it.

EDIT:
That one is infinitely adjustable because every temp sensor measures different. None of those old sensors were meant to be precise, or even repeatable. In the real world application I'll probably order a higher wattage handling 100k pot to make it reliable and last.
 
#23 ·
I used Rotella T6 synthetic because of its severe loads handling ability a while back. It behaved exceptionally well too. Surprised me actually. It was probably the best experience I ever had with motor oil in an air cooled ATV. But thats been a while and many of the good oils (including all the Rotella oils) have been altered in the last two years or so for whatever reasons. So its time for me to snoop around again, in case something better has come along..? Hard to keep up with all of the new tech advances nowadays.
 
#26 ·
I like that idea. Can you give me details on how you wired it and what part number it was? I understand a LITTLE about electronics, but a pretty good amount about electrical.

What temp did you settle on for the kick on point? Does the pot affect the fan off temp?
 
#29 ·
It has to be connected across the two oil sensor leads in parallel. So you would connect one wire from the 100k pot to the blue wire on the oil sensor, and the other wire from the 100k pot to the green wire on the sensor. I intend to make mine with plugs (scrounged from my old wiring harness with soldered leads) that match up to the existing wiring harness plugs and the oil temp sensor plugs for a "plug-it-in-and-play" affair. It'll be compact, weatherproof and professionally made.

Possible locations on the bike for putting it are somewhat flexible, since it can be plugged in under the oil sensor cover, or at the top frame tube where that sensor harness plugs into the main wiring harness. If you plug it in near the top frame tube, long chosen leads lengths could allow you to put it almost anywhere on the bike that is a relatively cool and dry area, yet is easy to access for quick adjustments.

You don't need to understand much about electronics... or anything else for that matter, really. Just do great work and you will always produce great products, that always work great. That is always true, no matter what you are doing. :)

Every oil temp sensor measures out at a different resistance than the other at the same temp... and every fan controller will kick the fan on at a different resistance threshold than the other at the same resistance... so there are no set "targets" for you to adjust the resistance signal that circuit sees to, from bike to bike. Follow me?

So, to allow for those differences between parts from bike to bike, the 100k pot you'll need is infinitely adjustable. You'll need to put the oil temp resistance mod on the bike and adjust the fan to kick on at (or around) a temp you'll choose yourself. You'll allow for a few degrees of range for the kick on temp target, because those oil sensors and fan controllers aren't precise enough to be precisely repeatable, to kick the fan on at an exact same temp every time.. I'll allow for about +- 10 degrees variance in kick on temp, for example, when I choose my target temp.

Does the pot affect the fan kick off temp?

Yes. If I understand the fan controller well (I think I do, I've built them from scratch before, with much tighter hysteresis, of course) the fan will be kicked out in a slightly tighter temp range than it would if left unmodded.

For instance: lets say the fan normally kicks on at an oil temp around 285 degrees (F) on our machine and normally shuts off when oil temp drops to around 235 degrees (F). The temp swing we are seeing from highest to lowest, is about 50 degrees on average.

We then add the mod to our hypothetical machine and adjust the pot so that the fan now kicks on around 215 degrees (F). We can now expect to see the fan shut down in less than a 50 degree swing from high to low... lets take a guess since we can't measure our make-believe machines fan shut down temp... say around a 40 degrees temp drop now... so around 175 degrees (F). So the hysteresis in the modded control system should tighten up some. We'll find out how much it tightens when one of us puts the idea to work in the real world.

The pot I tested this idea with was dug out of one of my parts bins, simply because it is an adjustable 100k trimmer pot. I'll attach the data sheet for that specific (size code is: 104) trimmer pot below, so you'll see whats going on here a bit better. But keep in mind that even though the Bournes pot that I chose to test this idea with is a good quality trimmer pot, it is rated for only 1/2 watts current handling max, if its working in a cool environment.

I will order a higher wattage handling 100k Trimmer pot to use in the real world application from mouser.com, because I want the pot to be reliable for decades on the bike.

Hope all this helps... Feel free to take the ball and run with it if ya want. I'd like to see how well it works on a 350. It'll be a while before I can finish up mine...

 

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#31 ·
oh come on now !..lol. I guess you worry if you gonna run out of gas ?, or run out of air in your tires too ?..lmao. give me a break bro !, NO ONE KNOWS IF OR WHEN SOMETHING IS GOING TO BREAK DOWN..UNTIL IT HAPPENS !..LMFAOOOO.
 
#30 ·
Note:

Trimmer pots have three leads coming out of them as shown on the data sheet for the one I tested with. On one end is the input lead, the center one is the wiper lead, and on the other end is the output lead. You'll use only two leads coming out of the trimmer to parallel with the oil temp sensor... the wiper lead in the center and your choice; of either the input lead, or the output lead, on either end. One of those leads on the end of the row will be NC. (no connection)
 
#32 ·
You live in the 'wilds' of Arkansas ........ I live in British Columbia.
Apples to oranges ...... you can't compare our circumstances/environments.
I will not depend on sensors that might/might not work. I will not let the oil in my quad get that hot, or go through those high heat cycles. A manual override of the fan fixes that.
Your statement on gasoline and air ........ just speechless here.
 
#33 ·
I do agree that it was a design flaw by Honda to allow the temperature to get as high as it does before the fan kicks on...
 
#34 ·
While a manual switch is good, for hauling heavy loads for extended time, for me it's kinda like my truck. The 6 spd transmission is automatic, cause I want the machine to do it for me. I can manual shift when I NEED to but want it to work like it should when I am driving around normally.

So Retro, did you have a part number or name for that adjustable resistor?
 
#36 ·
...So Retro, did you have a part number or name for that adjustable resistor?
I posted the datasheet image in a post above... It is a Bournes 100k ohms Trimmer Potentiometer. Read back up through the thread and you'll find it. You can search your supplier website and find it on the first attempt. I recommend buying a higher wattage handling capacity to rollout into the real world... this particular pot was a leftover from an audio amp that I built from scratch. I pulled it out of my parts bins only because it has the required resistance range for testing the idea, its not meant to be put to work anywhere high current loads could possibly exist. I recommend getting a beefier one at mouser or wherever you like to source your parts, to put on the machine.

...when you find what resistance provides the ideal kick on temperature for the fan, why not just wire an inline resistor of that numerical value? Cheaper, simpler, smaller
True, but you still need a trimmer pot plugged into the harness to learn that kick on resistance target, so why not just leave it there? Pots are tiny... I don't like to waste time and money buying parts I won't need and building things twice, especially if what I'm doing is redundant. This sounds so much like modern day china thinking to me.... design something that works, is full featured and is durable and useful, then swap parts out until its cheap to produce... but can't work as intended anymore. Makes no sense to me...

You'll also be eliminating a valuable time-saving and money-saving feature in doing so... no longer will you be able to compensate for resistance changes the oil temp sensor will go through as it ages. You'll no longer be able to change your mind when something happens in the real world that you hadn't thought out beforehand either... Universe eventually beats you over the head with it!

Other frustrating issues are introduced when you attempt to replace resistors to provide a precise known target value. The tolerances range from 20% down to 1% for precision resistors, tighter tolerance 1%'ers cost a lot of money... you'll have to tolerate buying a fixed resistor that is NEAR to the target resistance, but likely won't ever find one that matches exactly. Grab a handful of them and measure for yourself... each will be different. There are big resistance range gaps where you can't even buy fixed resistors for as well! Sometimes you need to buy two or three resistors and wire them together to reach a precise target. Its better to design your projects right, execute the assembly right.

You need to buy only one inexpensive component... leave the china thinking to the rats that exploit you with useless junk everyday.

The reason I typed out this long rant is because I want to help you (and anyone else stumbling in thats gonna try this mod) be successful. Please don't take my comments any other way...?

Have fun! :)
 
#35 ·
Retro,
A thought just occurred to me (strange, I know but it does happen now and then) when you find what resistance provides the ideal kick on temperature for the fan, why not just wire an inline resistor of that numerical value? Cheaper, simpler, smaller.
 
#37 · (Edited)
This 100k ohms Trimpot is rated for 1 watt. And it is a Bournes... so it is high quality. Thats why the price is $12.95 each, instead of 80 cents for useless china junk.. They can sell out fast so if ya snooze ya lose. :) There are many others that will do the job too... I spent only 5 minutes looking for this one... you may be able to do better if you put more time into it.



This one should survive for decades on the bike, provided its mounted away from high temps and vibration. The hotter the environment its gotta work in, the less power handling capacity it has. So put it somewhere easily accessed that stays cool on the bike and run your two leads to plug into the harnesses at the top frame tube near the fuel pump. Add an override switch (recommended) and/or an indicator light to it if you wish. This can go inside a small plastic box/tube/container of your choice (or right next to/with your over-ride switch) or simply attach it to the frame or harness or whatever you want to. Doesn't matter as long as it is secured and stays put.

The link to that Trimpot is HERE.
 

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#38 ·
Alright, I have a bit more free time now, so I thought I'd try to explain why I think higher power handling capacity in the trimpot is worth the much higher price for that component for this application.

Here are the 1/2 watt trimpot (that I tested this idea with) limits in-circuit; according to Ohms law, which has held up to all scrutiny as being accurate for quite a while now. :)
In this image I have entered 14.5 volts into the calculator (which is generally at/near max voltage the regulator/rectifier settles in at with the motor running) and 1/2 watt maximum rated capacity of the test trimpot. As you can see if resistance in-circuit ever drops below 420.5 ohms, the trimpot becomes overloaded and will fail. 10% of the trimpots rolled out in production will have probably already failed before the in-circuit resistance even drops that low.

This is key... remember, as the oil temp sensor heats up, resistance keeps dropping, until such a point is reached that the output power transistor is biased by rising voltage from the voltage divider circuit (or falling voltage, it can be done on the negative rail as well, and just may be so... but you get the understanding) inside the fan control, kicking on the fan. Once the sensor cools and resistance rises back up to a certain point, the fan control circuit opens and the fan stops. What if a condition (or set of conditions) come along that cause resistance to go much lower than normal? Universe loves to pull that crap on us... and will if we allow it. :)




Now lets find out how much more disaster prevention protection we can get from a 1 watt trimpot under those same (max) application conditions:




210.25 ohms. Now we are talking... Smoke that Universe! And if the motor is only idling on a fully charged battery we do even better:



Of course, during normal operation of any machine the oil temp circuit never goes that low... except in a dead short condition. We are buying extra disaster prevention protection here... such as a wire vibrating and rubbing on the frame and becoming bare...

And if a dead short condition ever happens our butt is covered! Hows that..? Because current always flows where resistance is least.... so the trimpot won't be easily smoked in a dead short condition elsewhere, cause all the available current will be flowing through the short. The trimpot is wired in parallel, not in series with any potential short.

If you just wish to mock up a test on your bike you can use the 1/2 watt trimpot. It may last for many years on the bike. But a 1 watt trimmer (or more than 1 watt if you prefer) will be a wiser choice, long term.
 
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