Hi everyone.
This is my first post... I have recently inherited a 1991, 3YF XTZ660.

The bike is nearly back on the road after fitting new inlet rubbers, carb ultrasonic clean and refurbish and replacement rear wheel and shock.

The bike now starts well and runs ok on idle, it warms up nicely, but does seem to get very warm, without the fan cutting in.

Not wanting to kill the engine before it even has an MOT, i removed the thermostat housing assembly to test the thermostat and thermoswitch.

The thermostat works well in a pan of boiling water, opening fully, the thermo unit (Gauge sender switch) also seems fine as the gauge operates to about midway but the thermoswitch (fan switch) doesn't change from infinite resistance to zero resistance unless i heat the end with a cigarette lighter for a few minutes?

the fan works when the thermoswitch contacts are bridged.

the manual states that the switch should operate from 105 degrees C, but a few minutes with a cigarette lighter seems like a bit more than that? unless it takes that long for the heat to conduct?

So, I bought a replacement thermoswitch which does exactly the same, so this leads me to think that Yamaha like their engines to get warm?

Does anyone know of another thermoswitch that would fit the existing housing that cuts in at say 100 degrees C? (212 degrees F)

cheers
Rob

Hi Bobby


I don't know of any switches that fit, sorry.

My fan NEVER came on in the 50,000+ miles I did when my bike was on the road, but then the temp gauge never went near the red.
The problem I had was getting the engine to warm up quickly 'til I made a bypass coolant circuit.

I should just see how it runs in real world conditions, maybe fit a switch to your handlebars just in case.

After all it is a made to run in much hotter climes than ours.

Rick

Cheers for the reply Rick

Perhaps i'm slightly paranoid with the engine temp. You're right....There are far warmer places than the UK. I always like to see the cooling fan kick in after refilling the system. Mainly to ensure there aren't any airlocks.

Looking into it a bit more....The 660 shares the same thermoswitch with many other Yamaha's. fZR1000's etc

I have managed to find a Suzuki Swift mk1 yellow housing thermoswitch that is an M16x1.5 thread and comes on at 100 degrees c and cuts out at 95 degrees, this should match up nicely with the thermostat which is fully open at 95 degrees.

Should give me a little peace of mind knowing that the engine will potentially stay 5 degrees cooler.

cheers
Rob