Temp fluctuations

I recently completed a resurrection of a '93 ST1100 that hadn't run since 1999. The forum here was a great help, especially for the carb rebuild. Anyway, the bike runs fine and I'm enjoying riding it. It's my first 'big' bike, having never owned anything larger than 650 before.

My question has to do with the temp. When I start and first ride - basically, until I stop the engine or stop and idle the bike - the temp gauge reads low. Almost low enough that I suspect I may have a sticking thermostat. At idle, the gauge will start to creep up until it's just above halfway. If restarting thebike after it sits for a few minutes, same thing - the gauge needle goes way up. As soon as I start riding again, gauge goes down and settles just below halfway, and heats up a bit more only when idling momentarily at a light.

Perhaps significantly, I have never heard the fan come on yet.

So question #1: Is this normal? Temps where I live are in 60s at the moment.
question #2: Can you hear the fan when it kicks on?

The bike did have coolant in the system when I got it, but I changed it out with new 50/50 mix.

One of my GL1000's did this when the temp sensor failed. Replaced the sensor and the fluctuations went away. Thought it was a sticky thermostat (still a possibility for you) but replacing it made no difference in the fluctuations.

My 1991 ST1100 stays on the low end of the gauge (it's 60's here as well) until the first time I stop for a light, then it rises to normal. Drops back down a bit when I take off.

Sounds pretty normal to me. At idle or slow speeds, the temp will creep a bit past the half way mark (~1:30) , at which point the fan should come on. You can hear it (listen closely) and the RPMs should drop a bit when it comes on. You can also feel it with your hand outside the left tupperware, below the false tank. When up to speed and cooling down, the fan will shut off just before the needle hits the half way mark on the way down (~12:30). At normal cruising speed, it will probably read at about the 1/4 mark (~10:30), depending on outside temperature.

1) Sounds about right, while moving below 1/2, stopped it will rise.
2) No; but, in the summer I can watch the temp rise and then fall when the fan kicks on while stopped at lights.
Come on out next year, or go to Death Valley and check it out!

Agree with everyone above. Sounds OK.

What everyone else said. The only time my fan will kick on is at extended idle on a very warm day. Then usually sink back into the lower side of the temp gauge at highway speed... even on 90+F days...

Odie1

Highwayman said:

Perhaps significantly, I have never heard the fan come on yet.

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I hook on that one:
The fan kicks in with the temp indicator a bit over 1/2 (like 1210hrs), and stops when the indicator shows like 1150hrs...
The needle will barely raise while on the move at over 40mph, but will jump up to fan cycling temps (see above) below that speed and in stop & go.
And yes the fan is audible while stationary, in idle brightness of dash illu and headlight, as well as RPM will drop slightly due the current drawn.

If the temp gauge goes beyond the 1210hrs, or even into the red mark, something is going wrong/not working.
The first to check would be low coolant level, as this exposes the temp probe to steam, thus gauge needle moves into the red field.

It's been said. Sounds normal.

The only thing I would add is that if your not sure whether the fan is coming on, here's a way to confirm.
Let the bike run on the center-stand, and popping up occasionally to check the temp gauge to avoid overheating, squat down on either side of the machine. When the fan kicks in, not only will you be able to hear it, but see it, and feel it, when the wave of hot air comes over you.
If it doesn't kick in by the time you are about 3/4 up the temp scale, that's when you need to look at the switching/power/mechanical movement.

Enjoy the ride!

paulcb said:

Sounds pretty normal to me. At idle or slow speeds, the temp will creep a bit past the half way mark (~1:30) , at which point the fan should come on. You can hear it (listen closely) and the RPMs should drop a bit when it comes on. You can also feel it with your hand outside the left tupperware, below the false tank. When up to speed and cooling down, the fan will shut off just before the needle hits the half way mark on the way down (~12:30). At normal cruising speed, it will probably read at about the 1/4 mark (~10:30), depending on outside temperature.

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+1 On mine, the fan seems to kick in at about half scale. It should definitely come on if you let it idle on the center stand after a ride. But on the slab, it reads way, way downscale.

If the fan isn't coming on, check the ground wire connection on the fan assembly for corrosion. If you pull the wire from the temp sensor on the radiator and connect it to a good ground, the fan should kick in.

Thanks for all the replies. I have confirmed that the fan does come on. In fact, as suggested, I just put it on the centerstand, started it and watched it go through the cooling process. Temp needle goes up to about 2/3, at which point the fan comes on for about 30 secs, temp goes down to about 1/4-1/3, fan goes off . . . and so on. Again, this is in coolish ambient temps (low 60s, which is considered freezing out here in CA). When I'm moving, temps stay right around mid-guage, plus or minus. So as suggested by you all, I think I'm good. If I have future issues, I will check the temp sensor as suggested by Oldbikefixr.

I only brought this up because I've owned a bunch of Honda/Acura cars and on all of those (as well as Toyotas, Nissan, Mazda, etc) the temp gauge - when everything is working as it should - goes to halfway and just stays there. So I'm just not used to seeing this much movement. Guess I'll get used to it.

I don't think you have a situation that will cause any real problem. But I think you may ( maybe ) have a bad temp sensor ( not the fan switch ). I believe the gauge should be reading closer to 12:00 when the fan kicks in. Unfortunately, there is no spec for the resistance at 70F or 212F in the Service Manual.

In a few days, I'll pull mine and take the measurements for future reference.

Jim Van said:

I believe the gauge should be reading closer to 12:00 when the fan kicks in.

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I was thinking the same thing; my fan comes on just past high noon..

Highwayman said:

When I'm moving, temps stay right around mid-guage, plus or minus.

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Well, I'd agree on a possible offset of the temp probe, connectors or instrument...

I only brought this up because I've owned a bunch of Honda/Acura cars and on all of those (as well as Toyotas, Nissan, Mazda, etc) the temp gauge - when everything is working as it should - goes to halfway and just stays there. So I'm just not used to seeing this much movement. Guess I'll get used to it.

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Two significant differences on car engines:
- a way larger water-jacket/amount of coolant in the system being quite inert
- temp gauges won't fluctuate/exceed particular indications by design to not agitate the operator (I kid you not...)

The ST1100 holds 3 ltrs(!) coolant (+0.5 ltr in expansion tank), with that low amount fluctuations are normal.

I thought the Temp probe for the Gauge and the temp switch to kick the Fan on are separate. If that is true perhaps he just has a switch that kick in higher.

That's possible too. But maybe the gauge reading is just off. Could be either. I'm going to get the resistance readings from my therm sensor ( thermistor) and then others can compare.

Slydynbye said:

If that is true perhaps he just has a switch that kick in higher.

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IMHO not as likely... that Klixon-design rather fails completely (not turning on) then altering its setpoint...
BTDT on my '92... all over sudden the temp needle went to fully right... I first darted down the road with 60+ to cool the engine down by airflow, to then stop and diagnose the issue...

ST1100Y said:

IMHO not as likely... that Klixon-design rather fails completely (not turning on) then altering its setpoint.

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I've been trying to chase down some erratic temperature behavior on my 1100 and decided to test the fan switch. Per the manual I tested for continuity while the switch was in boiling water and it did not close. It would close when held over a flame and reopened when it cooled. My conclusion was that the setpoint had changed to a higher temp than specified. FWIW.

MV_Dave said:

I've been trying to chase down some erratic temperature behavior on my 1100 and decided to test the fan switch. Per the manual I tested for continuity while the switch was in boiling water and it did not close. It would close when held over a flame and reopened when it cooled. My conclusion was that the setpoint had changed to a higher temp than specified. FWIW.

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Sounds suspicious to me; not sure I want my bike to get hot as a flame before the fan comes on..