2000 big bear 400 2wd.

Oil cooler fan never kicks on.

If I pull the plug off the sensor and bridge the terminals the fan will start. That tells me the relay and circuit are probably fine.

When I test continuity on the sensor at room temp, I get a reading.

So sensor is shot I’m guessing?

If that’s in the budget, can I just manually run it all the time while the atv is running and be ok?

 

You can run the fan all the time, several of the bikes we maintain have been modified by their owners to do this. I find it is an annoyance, and of course, takes a fair bit of power from the battery, though the alternator should cope OK. Just checked and partzilla are selling the temp units 4GB-83591-10-00 at $81 still seems expensive but list price is $114. The resistance test you did seems wrong, with resistance as low as 7 ohms I think the fan would be on all the time. Yam spec is 307 to 339 ohms at 150 degrees centigrade and 209 to 231 ohms at 170 degrees centigrade, tested with bulb in a pan of hot oil. Circa 150 degrees C seems awful hot before the fan comes in but that is what the test implies. I assume 170 degrees C is when the light comes on.

 

Thanks Merryman, not sure why I can't see your response here, but the email had all the details. Do you guys just jump those two wires together at the sensor to trick it into running all the time then?

 

I have seen all sorts of "Heath Robinson" ways of getting the fan to work all the time, but jumping the wires to temp sender seems easiest, I suspect on an air cooled Yam, this will fetch the warning light on too and, knowing Yamaha, may affect the ignition timing as they love to wire everything into the CDI. Is it possible it just hasn't got hot enough to fetch the fan in? As I wrote above, 150 degrees Centigrade seems very hot, water cooled engines usually run circa 100 degrees centigrade.

 

Well I rode all day on Saturday, 103 outside. If it didn’t come on then I don’t know when it ever would. I heard the fans on some other Honda atvs kicking on all day.

 

So put a lighter under it with the ignition on, and sure enough it kicked on. Now I need to heat some oil and figure out at which temp it actually kicks over on.

 

Had to heat some oil up to 300 degrees F to get it to kick on. But kept running until it was down to 170 before i pulled it out. Dropping it back into 170 didn’t re-engage the fan.

 

Looks like a new switch is called for then, unless the relay is playing up and not switching at the correct resistance, if you could trust your ohm meter to give the correct readings, you would know, but I find ohm meters wander all over the place, never reading the same twice.

 

Guess I can try to identify and price that relay, worth a shot. I got a 2nd used sensor and it basically did the same thing.

I ran around for 30 mins or so and measured oil temp, it was around 160f.

 

Please note, I was quoting Centigrade values from the manual, you seem to be measuring Fahrenheit.