Radiator fan doesn't work

This is a REALLY stupid realization to have after having this bike for almost 4 years, but I'm pretty sure the fan has never worked. What a moron. Well, it's getting hot now and I'm ready to tackle it. Here is my order:

1. Check fuse
2. Check thermostat
3. Check motor

Is that correct?

Thanks!

after checking the fuse, pull the single pin lead off of the temp sensor on the lower part of the radiator, and ground it to the engine. If the fan doesn't run, then start tracing out the wiring to the fan.

also open the radiator at the cap and verify the fluid level isn't low.

dwalby said:

pull the single pin lead off of the temp sensor on the lower part of the radiator, and ground it to the engine.

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It should run then. In case it isn't obvious, the ignition should be switched to the on position while the sensor's lead is grounded to make the fan run (normal operation/function). You always give good advice, Doug. Just chiming in to cover Murphy's Law, 4th corollary.

John

So when I say thermostat, I really mean the temp sensor. Right? I hate using the wrong vernacular.

bikerdrumr said:

So when I say thermostat, I really mean the temp sensor. Right? I hate using the wrong vernacular.

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The thermostat is in a housing just behind the radiator cap. You can't actually see it without disassembling its housing.

The temp sensor is threaded into the same housing as the thermostat, it has a single wire connector attached to it, and it drives the temp gauge in the instrument panel.

The thermo switch is threaded into the back of the radiator, and is what turns the fan on. When the radiator coolant temp gets high enough the switch shorts to ground and completes the fan electrical circuit, turning on the fan.

John OoSTerhuis said:

It should run then. In case it isn't obvious, the ignition should be switched to the on position while the sensor's lead is grounded to make the fan run (normal operation/function). You always give good advice, Doug. Just chiming in to cover Murphy's Law, 4th corollary.

John

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Yeah, I'm never sure where the line is between too much information and just enough. I usually err on the side of too much, but this AM I was short on time so I kept it brief. Now I'm at work, so I have plenty of free time

OK, fuse is good and I got the fan to work by connecting the wire from the thermo switch to the frame. So, it seems as though I have to test the thermo switch with boiling mixture and an ohmmeter as it's described in the Clymer manual. Either that or pay $61 for a new switch.

check the coolant level in the radiator (not the overflow tank). If you let it get really low its possible that the switch is sitting in air, not coolant, and it won't respond as designed. Hopefully, that isn't the cause, but while you're testing everything this is one more variable that has to be addressed.

Yes, check the coolant level at the radiator fill cap (yes, some Tupperware to remove, you own a fully faired motorcycle, get on with it). Top off with coolant if necessary. The next step is to run the bike until the gage gets to vertical or a bit more and listen-to/watch-for the fan to run. Report back.

The rad had plenty of coolant and the system had no air in it when I went to burp it. However, the overflow reservoir was dry. I added fluid up to the specified level. There is no evidence anywhere of leaking. When the bike's gauge goes to vertical, the fan doesn't turn on. At this point, when I flush the system in a couple weeks I think I'm just going to spring for a new fan switch. The temp sensor is only $8 so I might change that as well. Didn't someone say that you should change your radiator cap every several years or so? This bike is 17yo and has 72k miles. Am I due?

Unfortunately, I don't have time to sort all of this out at once. So every chance I get to work on it, I do.

the fan won't come on at exactly vertical, it has to go a bit past vertical. You never did say if the gauge keeps climbing well past vertical, should we assume that it does, and the fan still doesn't come on?

If so, it sounds like you need a new switch, but $61 sounds way too high, $36 is more like it.

I've never had the time to see just how far the needle will go. I'll just say I've NEVER heard the fan ever, or felt the heat blast of the engine because of the fan. That $61 quote is from an auto parts place. I'll check online.

bikerdrumr said:

I've never had the time to see just how far the needle will go. I'll just say I've NEVER heard the fan ever, or felt the heat blast of the engine because of the fan. That $61 quote is from an auto parts place. I'll check online.

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its not clear that you actually have a problem given what you've told us so far. Unless the needle is climbing past vertical, the fan should be off, are you saying you've never actually watched it go past vertical?

In normal riding it doesn't get close to vertical, it only reaches that zone when stopped or slowly moving through traffic. If it gets to anything beyond vertical, then the fan should come on, but it may have to move a needle thickness or two past vertical to trigger the switch (by 3/4 for sure it should be on). If it gets to just around vertical, or a tiny bit higher, then drops back down as your speed picks back up again, then that's normal, the fan shouldn't come on.

My apologies. In stop & go on a day above 85F, the needle HAS gone past vertical. Using a scale of 0% is needle pinned to cold, 50% is vertical, and 100% is needle pinned to hot: idk if it's ever hit 75%, but I'm sure it's been between 60% & 70% and the fan still hasn't come on. Riding on the hwy today in 90F weather, the needle usually stays around 25%-35%. In that situation, I would never expect the fan to operate. Hopefully that gives you more explanation.

I'll let the bike idle right now and get back to you.

OK, FOLKS! Please go about your business. There's nothing to see here...just a complete idiot!

Yes, the fan works. BUT LET ME EXPLAIN!!! (I am feeling REALLY stupid) The bike I had before '01 Triumph Sprint, when the fan came on, it was strong, loud and you felt the blast of air. I've heard other bikes fans as well. With the ST, it took me a flashlight in broad daylight just to see the fan operating. So, apparently it's very quiet and it's hard to see. Ugh. Oh, and I found vent in the fairing where the fan blast is.

Hopefully some of you at least got a chuckle out of this. Please feel free to post "point and laugh" smilies. I deserve it.

In my experience will the needle stay well on the left side of the dial while moving anywhere above 60kph/38mph, as there is sufficient air-flow through the radiator.

Only when moving in slow traffic or while stationary the needle will start to climb up to the centre of the dial.
Referring to an analogue clock at aprox 1210hrs the fan kicks in, once the needle has dropped to about 1150hrs the fan stops again.
If the needle moves above 1210hrs something is off, likely low coolant level as the temp probe (located on the highest point of the system) is then exposed to steam instead submerged in liquid.

You'd mentioned a "dry" expansion tank, so I'd keep an eye on that and check for any leaks, as the coolant must have gone somewhere.
Hint: cold engine -> coolant level on MIN mark; fully warmed engine (= fan cycling) -> coolant on MAX marking.

Can confirm, the only time I've heard my fan come on is when I stopped the engine.

<chuckle>

John [who's had his own share of "Doh!" moments]

bikerdrumr said:

So, apparently it's very quiet and it's hard to see. Ugh. Oh, and I found vent in the fairing where the fan blast is.

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Yeah, its not really obvious when it kicks on in traffic with a lot of noise around you. Next time its getting ready to kick on look closely at the tach and listen to the engine sound. When the fan turns on you'll probably notice a very slight decrease in idle speed that you can hear, and you may see the tach needle drop ever so slightly. With gloves and jacket on I'm not even sure you can feel the air blast coming from the fairing vent.

p.s. your beer money fund just grew by $61, congrats.

dwalby said:

Yeah, its not really obvious when it kicks on in traffic with a lot of noise around you. Next time its getting ready to kick on look closely at the tach and listen to the engine sound. When the fan turns on you'll probably notice a very slight decrease in idle speed that you can hear, and you may see the tach needle drop ever so slightly. With gloves and jacket on I'm not even sure you can feel the air blast coming from the fairing vent.

p.s. your beer money fund just grew by $61, congrats.

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+1. The only way I know my fan comes on is the tach drops about 50 RPM and the temp stabilizes and then starts to drop.