Cooling Fans - Cable fuse?

[iktank]

Fans work when I short the two black cables to radiator switch
The fans do not switch on when the temp gets so hot that the red temp light comes on

Does the fan switch need repalceing ?

ta Ian

[den]

hi , you're almost there , you've established the fan works , and theres electric,,so now finish off testing the switch,,just the same as any switch,,create a small circuit or use a multimeter and pop the device in a cup of boiling water,, wait a sec and you'll see the meter come alive or your lightbulb/pp9 battery circuit light up,,remember not to short the terminals out with water,,that will give you a false reading,,

[DAVID THOMPSON]

my traveller very seldom get warm enough to make them come on....
but it seldom gets over 90 to 95 deg F where i live

but boy does it get humid here
dave

best to make the fans run by back feeding them so the lube in the bearings does not set up
as part of your service

[iktank]

Still having issues with my fans not kicking in, the red temp warning light comes on but fans do not?

Fitted a new switch and the fans work when I short the two black cables to this radiator/fan switch, tested the switch and it does work

Are the two sensors on the rad interconnected -

Any idea ??

[iktank]

Been looking throught the cable drawings and there is apparently a CABLE FUSE

Has anyone come across this in the loom? Rough location would be helpful

[Bill Jurgenson]

the ignition does not need to be turned on for the fans. The fans are connected thru the 15amp fuse directly to the battery and are not turned on or off by the key.
The warning light is.
The two thermal switches have different temperatures: the fans turn on at 85-90º C, the warning light at 105ºC so, no, they do come on at the same time.
Both thermal switches connect to ground, the fans thru their own separate fuse. To check the fans, connect the two shoes at the switch together with a piece of wire. you will also have to check that separate fuse if they do not run. Depending on year, that fuse is in different places: early models have a glass fuse holder directly above the radiator- hard to get at - and this has in many cases "fused" together due to the heat there, since it is also directly above the exhaust headers. This is very often (almost always) the reason the fans do not work. Later models have a blade fuse under the seat for the fans. Replace this fuse with an inline blade fuse holder under the seat and new wire directly connected to ground if you have one of those models.
If the fans do work when shorted, chances are either your engine never gets too hot, or the thermal switch is a dud. Both are possible. If the warning light does work but never comes on, the it is very probable that the motor never does get too hot since it is highly improbable that both thermal switches are duds. You can check the switches by removing them and heating them while connected to a multimeter set to measure resistance (or to beep). it will go to zero (or beep) if the switch cuts on. The switches do go bad and are standard automotive units with standardized threads. Obviously you need the correct heat range and thread.
Except in hot summer city driving, the fans never run - or shouldn't. On the contrary, the Skorpion has more of a problem of not getting hot enuf.
Some people install a thermometer instead of that useless clock and a toggle switch to turn the fans on as necessary. Except in Cairo and Santa Fee, there is no reason to have two fans at all. Many also have only one fan, keeping the other as a replacement when (inevitably!) the fan goes bad. that way they last twice as long.

[iktank]

Thanks Bill - the knowledge bas as always

What I dont understand is why if I bridge the two black cables to the fan thermal switch the fans come on?
Can I be unlucky that the replacement thermal switch I fitted is also faulty

Only thing i can do is to take it out and test it

Thanks again

[Bill Jurgenson]

they should run if you bridge the connectors as you say.
the switch could be defect. I should switch at 85°C, the other for the wsrning light at 105°.
simple enuf to test; remove it, hook a multirester to the connectors and heat it up e. g. on the stove.
Both are completely standard automotive thermal switches, nothing MZ-specific about them. I get replacements from a car parts jobber. All you need is the heat range and threading. the last ones I got were for GM cars.

[Bill Jurgenson]

btw
I ran my Skorpions with no fan at all. The fan on my SZR never once came on!
my present Skorpion is air-cooled.
whatever.
the thermostat in the water hose is a joke both on the MZs and the SZRs.
it has bypass holes which allow about 40% to flow at all times. For this reason, the motor in both types takes ages to get warmed up and never really gets warm enough except while waiting at traffic lights at temperatures above 90°F. The Yamaha never. Using a thermostat housing from the FZR and some hosing, I rebuilt all of my XTZ-engined bikes to have a real thermostatically controlled system (like a car) in which the water circulates only in the motor until the thermostat reaches temperature to open and allow the coolant to flow thru the radiator.
the modification is simple and well worth the effort. The bike reaches 80/90° in 10minutes and keeps that temperature.

[Bill Jurgenson]

Two pictures from the Yamaha but the Skorpion is basically the same. The T-junction bypasses the radiator. As long as the thermostat remains closed, the coolant does not run thru the radiator. In the top shot, you can see the hose coming from the cylinder head and connecting to the thermostat housing as well ans the additional hose running back to the T-junction and so directly to the engine. Only when the thermostat opens does the collant run out thru the top of the housing to the radiator.

Additional bonus: the thermal switches are in the thermostat housing and so reflect the actual coolant temperature, unlike those on the MZ which of necessity can only meter the radiator itself which is of course cooler.

[iktank]

Thanks Bill
Think I will do as you suggest over the winter, just want get out and about while weather good

I took of the new thermal switch and it does not open so faulty
Checked red warning light and it comes on at 102 degrees celcius

Been to local motor factors with my thermal switch in hand - very unhelpful and would only look if I had a model of car it came off - NO IDEA !!!!

I have done some ggoling but cannot find a car with M10 thread fan switch - plenty with 14mm or 22mm

Any of you nice people got a definitive car model that it cam off
- !987 BMW 3 series has a 14mm thread

[rodge70]

if it's any help,i think my trailtech registers about 107c before the fan fires up on my baggy and usually only when in slow heavy traffic will it get that hot and soon drops when on the move again.

[iktank]

Found radiator fan switch that kicks on at 85 degrees C
Lucas Part Number - SNB1187
Only cost £6.32

All fitted and all working