Fan Temperature

Hi experienced VF1000F owners! I just recently bought a 1984 VF1000F. I had it running in my garage for a while last week. The temperature gauge got pretty close to the H Mark and the fan still wasn’t on. When does it usually come on on these bikes? I don’t want to install a manual switch for it. I would rather it to come on automatically but I’m not sure when it should.


Hi Jason,welcome to the wonderful world of the VF.
By the time the gauge is at 3/4 I would expect the fan to be running.
The actual temperature for fan on is too high IMHO (about 105)
If you look in the owners lounge section there are details of a switch that operates at 92
Worth checking the fan is operational by bridging the thermostatic switch terminals with the ignition on.
There are no relays in the circuit the thermo switch connects directly to the fan.
Hope this is of some help,regards Bif

Hi Bif. That’s some great information. I’ll try to find the 92 degree switch and in the meantime I’ll bridge the wires to the switch on the bike now to test the rest of the fan system. I have a CBR1000 as well and the fan comes on at 102. Not too far off the 105 but I even find that to be a little hot! Thanks for your quick and informative response!

Just a little update on what I did. I ordered one of these from China -

It took a while for it to arrive but it threaded in nicely and the factory wiring harness plugs right into it. I bent one terminal on it slightly because it doesn’t have the clip part to keep it on. Feels like a nice solid connection now. I’m not going to have to worry about it coming off. I tested it in a pot before installing and it closes the switch at about 87c. Perfect. :slight_smile:

That switch looks like it turns on at 80c - I think that is below the temp the thermostat opens at. There may be problems with the thermostat closing during riding.
I thought that the best temp for the fanstat to turn the fan on was 95c. No where near the 110c that the honda switch closes at.

Thanks for your comment on this thx113. You definitely have me thinking about this. I thought that when the coolant in the engine heats up to the temperature rating for the thermostat it would open up. Then that coolant would go to the radiators which will have the fan on at a lower temperature. That then slightly cooler coolant would flow back into the engine where it will heat back up and so on. I thought thermostats could open and close many times on a ride in some conditions. On a hot day sitting in traffic it may stay open all the time with the fan on continuously. Am I thinking about this wrong? I’ve been looking at the coolant flow diagram and working it out through my brain.


The previous owner of my bike had a switch wired up to turn the fan on. I didn’t like that although I know there are some riders that prefer this. I don’t want to rely on my own senses to turn the fan on. Plus I just want to enjoy my ride and not have to think about that. There’s enough to think about when riding a motorcycle in my opinion.

Please share any thoughts on this.


Looking at flow diagram the fanstat switch is just on the output side of the thermostat. So as the thermostat got warm enough to open, the fan would come on and cool things down again.
I think that over 90 is still a better idea. maybe you can put a resistor across the contacts to raise the temp slightly.

The stock Honda Thermo-Switch is set for 110’C, way too hot.
The carbs start cooking and the Engine sputters.
Takes a while for Temps to come down from way up there.
The Fans come ON when the needle is about 3/4 way up the Gauge.

So I found and ordered a 95’C Thermo-Switch;

Fans now come ON when the Gauge is 1/2 way up.
Cooling happens faster too.
I would like the fans to come ON even sooner (90’C?).
Somewhere I saw the Switch Temp is set for 95’C but ±5’C.
I think the Thermostat is set at 88’C?, so a 90’C Switch would work, but might come ON a lot.

This is still much better than Stock.
These were the last 2 shown in stock (
Don’t know if they will restock, but equivalents should be around.

I’ll install Switch #2 on Bike #2 and see if the gauge action matches.

I’ll have the one bike in the Eastern Oregon desert in about a month, will see how it works.
That bike also has a Manual Fan Switch (with Indicator Light, or else I forget) as backup.
Also rember to have a new O-Ring handy (13.5 x 1.4)

Found a couple old Thermostats.
Looks like factory design is to start OPENing @ 82’C

So maybe a 90’C ThermoSwitch would work fine?
Its that ±5’C that is a wild card.

Hello having a similar issue with my 84 vf1000f. That switch you ordered, it fit without adaptors in the original hole in the rad tank?

I put this one in mine. Threaded into the original hole and turns on at 80°C. I can’t remember if the connector fit on it or if I wired up spade connectors to the original connector. Works great and comes on at a much lower temp.

Forgot to post the link to it:

Thanks! I ordered one. Appreciate you answering so quickly.

These ThermoSwitch types can have a error of ±5’C which means it might come ON at 75’C.
Would mean the Fans run All the time.
Easy enough to check, hook up a lamp (LED+470 ohms) across the fans, will Light Up when the fans run.

It probably does but I haven’t seen any harm in the fan running more often. The bike still goes up to a good operating temperature and the fan is quiet anyway. At least it’s not on a manual switch that I need to manually toggle and could potentially miss sometime as the temperature gets high.

The temp bulb in the thermostat housing is for the temperature gauge. The fan switch is fitted to the upper radiator.