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Discussion Starter · #1 ·
Hi Gang, recently purchased a 2000 foreman TRX450ES

Is the oil temp light supposed to turn on when you turn the key on but the engine is not running? Mine does not come on at all.

when I got it it had very low compression (like 20)

Rebuilt top end (it was obvious it was over heated based on the piston condition.

I just got it running and it runs great, but I want to make sure the oil cooling system works correctly.

I did a number of tests on the system based on my repair manual and the bulb is good (because if I ground the blue\red wire from the oil temp control unit plug to ground the light turns on and all the other wiring tests check out good (green wire is connected to ground), so if it is supposed to turn on when the key is on (and unit not running) then from what I am reading in the manual it seems I need a new control unit, but wanted to be sure before I spent $140 on a new OEM one (after markets ones are about 60 on line but would rather get oem).

If I run all the other tests the manual has on the wiring it all checks out good EXCEPT that the resistance on the oil temp sensor is not what the book said, but neither was the temp. It should be between 10,000-9,500 ohms and mine is about 13500. The engine is cold. it is about 70 outside now and book says it needs to be at 77 for the reading. I ran it around the yard and warmed it up, not a over 77 for sure and retested and got about 7500 ohms, so I am thinking the sensor is ok as the manual says warmer is lower, colder is higher, then as it cooled off the numbers got higher again, but I have no way to know really when the engine is at 77 deg,

Second question, does this sound ok or should I change the sensor too?

the manual had some other wiring type tests on the cooling system and they all check out.

If I put power to the fan wires the fan turns on as well.

Thanks in advance for the input
 

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If I were fixing your machine for you, I would insist on replacing both. Why? Because once the oil overheats seriously, the oil temp sensor resistance changes permanently. It will no longer track resistance vs oil temp linearly & accurately. This is a common trait (an artifact of its design) with all variable resistance temperature sending units from all manufacturers, not just Honda's.

So, replace them both if you suspect that the oil has ever been overheated, as in this case. I recommend putting an override switch on the bike so you can switch the fan on manually while you are working it hard to keep oil operating temps reasonably low. Any oil temp over 220-230 degrees (F) can potentially destroy the motor oil so keep that in mind... if you ever overheat the motor oil change it out immediately.

Welcome to the forums!
 

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My shop 99 450S had an intermittent oil light it would come on at random. I replaced the fan control unit ($187 OEM) only; service tech told me he was going to change temp sensor too but didn't charge me for it if so.
Oil light comes on just for a bit prior to starting. On the road again
 

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I'm not saying one way or the other whether you should replace the sending unit. My only comment is that when you first turn on the key, the sending unit is ignored, and the oil temp light comes on for a couple of seconds anyway. Therefore, if your temp light doesn't come on after turning on the key, it is not because the sending unit may or may not be bad. The problem sounds like a bad control unit.
 

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Discussion Starter · #5 ·
Thanks for the replies, Looks like I better order some parts. I will put on an override switch as well. I did that with my DS650 and put a light on the dash that turned on whenever the fan was on as well. I think I will do the same for this unit.
 
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