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Discussion Starter · #1 ·
Hi anyone ,

I have TRX 350 1987 and recently replaced thermostat (temperature) sensor that controls cooling fan (sensor located on the lower right side crank case). I was told by the technician that it takes a long time for the sensor to kick in and cooling fan to start working (design failure according to tech.). I ran engine for one hour (today in Florida 90+ degrees)and cooling fan never started. Please anyone on this issue. In addition cooling fan is working and it is tested.
 

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That may be normal. They're designed to kick on when the engine starts to get hot, not at normal operating temperature. If you are running the engine real hard or pulling something, then it should kick on.
 

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The fan is actually for the oil cooler right? no Radiator. I would check the relay and make sure it is good if it has one. if you still can't get it to work just by pass the temp switch... Wire in a relay and a toggle switch and turn it on when you go ride. simple fix.
 

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The fan is actually for the oil cooler right? no Radiator. I would check the relay and make sure it is good if it has one. if you still can't get it to work just by pass the temp switch... Wire in a relay and a toggle switch and turn it on when you go ride. simple fix.
Yeah, the fan is for the oil cooler. They aren't water cooled. It should have a relay or control unit somewhere. Shadetree will probably be able to tell you when he gets on here. He just restored one of those ATVs like yours.
 

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yeah ram..i just restored my trx350d foreman..and it takes alot of heat..around 400 or 500 f to make the oil cooler fan to come on..you can't let the bike just sit there at idle for an hour..and expect the fan to come on..won't work..you need to ride it hard..get the engine really hot..then the fan should come on...if it doesn't..then the fan control relay unit is bad..it's under the front fender..front left..at least thats where mine is...this relay not only controls your fan..when your oil get's too hot..but it also will shut your engine down if the oil cooler fan doesn't work for some reason..it's a safety feature they built into the bike.
 

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yeah ram..i just restored my trx350d foreman..and it takes alot of heat..around 400 or 500 f to make the oil cooler fan to come on..you can't let the bike just sit there at idle for an hour..and expect the fan to come on..won't work..you need to ride it hard..get the engine really hot..then the fan should come on...if it doesn't..then the fan control relay unit is bad..it's under the front fender..front left..at least thats where mine is...this relay not only controls your fan..when your oil get's too hot..but it also will shut your engine down if the oil cooler fan doesn't work for some reason..it's a safety feature they built into the bike.
Yeah, there you are. I knew you would have the answers he needed.
 

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yeah ram..i just restored my trx350d foreman..and it takes alot of heat..around 400 or 500 f to make the oil cooler fan to come on..you can't let the bike just sit there at idle for an hour..and expect the fan to come on..won't work..you need to ride it hard..get the engine really hot..then the fan should come on...if it doesn't..then the fan control relay unit is bad..it's under the front fender..front left..at least thats where mine is...this relay not only controls your fan..when your oil get's too hot..but it also will shut your engine down if the oil cooler fan doesn't work for some reason..it's a safety feature they built into the bike.
Yeah, there you are. I knew you would have the answers he needed.
lol helmut..been kinda busy around home here..haven't had time to give out good info on here lately..but..thanks..i sure do know these trx350's..i love mine to death bro..she's as good as it gets !..anyway..i'll try to drop in from time to time..i'm currently rebuilding a yamaha < yes..i said yamaha !..lmfao > don't shoot me..it's a jet ski..and i got it free..soo..i can't complain..lmfao..waitting on parts to come in..then i'll be really busy on it for a few days..lol..anyway..hope i helped him out on his bike.
 

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Discussion Starter · #9 ·
oil cooler

yeah ram..i just restored my trx350d foreman..and it takes alot of heat..around 400 or 500 f to make the oil cooler fan to come on..you can't let the bike just sit there at idle for an hour..and expect the fan to come on..won't work..you need to ride it hard..get the engine really hot..then the fan should come on...if it doesn't..then the fan control relay unit is bad..it's under the front fender..front left..at least thats where mine is...this relay not only controls your fan..when your oil get's too hot..but it also will shut your engine down if the oil cooler fan doesn't work for some reason..it's a safety feature they built into the bike.
I did not realize that it takes that long, thank you for the info.
 

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yeah ram..i just restored my trx350d foreman..and it takes alot of heat..around 400 or 500 f to make the oil cooler fan to come on..you can't let the bike just sit there at idle for an hour..and expect the fan to come on..won't work..you need to ride it hard..get the engine really hot..then the fan should come on...if it doesn't..then the fan control relay unit is bad..it's under the front fender..front left..at least thats where mine is...this relay not only controls your fan..when your oil get's too hot..but it also will shut your engine down if the oil cooler fan doesn't work for some reason..it's a safety feature they built into the bike.
I did not realize that it takes that long, thank you for the info.
Here is how the oil cooling system/fan/temp sensor/control unit works on the Fourtrax/Foreman 350.

 

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yup..that be it helmut..like i stated..you reallyyyyyy have to ride/work the bike..and get it hot enough for the control unit to kick in..and turn the fan on..just idling won't cut it.
 

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Where'd you get that spiffy diagram Hemlut? Lol. Anyways I'm having the same "issue" as this with my bike and like the others say it simply wont kick in at idle. I let mine run for like 20 minutes reving it up every now and then and i could stick my finger in the oil no problem without it beeing too hot. As far as the 500f to 600f I dont know, but the manual says the fan should kick on when the oil temp reaches 270f to 306f and the oil temp light should come on at 378f to 414f. If you want to check your sensor just to be sure, you can put it in a pan of oil and heat it up on the stove. resistances should be as follows; 77f = 9500-10500 ohms, 212f = 950-1050 ohms, 338f = 209-231 ohms. Hope this helps
 

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Where'd you get that spiffy diagram Hemlut?
I bet you seen that before. LOL.
 

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hi this fan and oil cooler looks like a great ida i have a 1986 fortrax 250 i dont have a fan or a oil cooler? can i install this set up in my atv??? thank u
 

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hi this fan and oil cooler looks like a great ida i have a 1986 fortrax 250 i dont have a fan or a oil cooler? can i install this set up in my atv??? thank u
I don't think you can buy a bolton fan or oil cooler for the Fourtrax 250. You would have to find one from another ATV and fab mounts for it. It would probably be a little hard to hook the lines from the oil cooler up to the engine as you would have to fab something there also. The fan you would have to wire up to a toggle switch as there would be no way for it to kick on when the engine gets hot. You would have to activate it manually. I used to own 2 Fourtrax 250s and honestly, mine never ran at all hot and I didn't need an oil cooler or fan.
 

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Hey guys Im new and you just answered the question no one else could, the cooler fan and when it should kick in. Thanks Tom
I just bought a 1986 350 Fourtrax, the plastic is great, great compression, needs new tires, all in all a good bike. I paid 1300 for it and think I got a good deal.
 

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Hey guys Im new and you just answered the question no one else could, the cooler fan and when it should kick in. Thanks Tom
I just bought a 1986 350 Fourtrax, the plastic is great, great compression, needs new tires, all in all a good bike. I paid 1300 for it and think I got a good deal.
Welcome to the forums. The Fourtrax 350 is a great quad. Glad you found what you were looking for.
 
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