Thermoswitch

[BlueDog]

How do I test the various senders to see if they work or not? Specifically the radiator cooling fan thermoswitch. Same question for the cooling fan relay.
This is likely dumb but electrical stuff is not my bag.
Thanks.

[bscutt]

To test the relay, unplug the wires from the thermoswitch and short the two contacts (of the wires you unplugged) with another piece of wire or a paper clip. If the fan cuts on the relay is ok.

To test the thermoswitch you need a multimeter or something to test continuity with. remove the sender and put it in some hot water with the continuity checker attached. The switch should give a continuity indication some time before the water boils. If you have a thermometer that measures up to 240F I think the thermoswitch should make continuity around 210 degrees or so.

Otherwise you can just leave it in and watch for your fan to come on when the engine gets hot. It should turn on somewhere around 3/4 of full scale on the temp gauge.

[surfcam]

I was in the same bag and use to avoid electrical problem like the plague. Then I bought a Haynes Techbook an Automotive Electrical Manual. Now I have the basics and can solve 95% of my problems.
The first thing I would do for your problem is turn ignition on. Then jumper your thermoswitch. Be careful of the fan it might come on. If it does your switch is bad because its not coming on went your up to temperature either right. If not you have to look in other directions. Then check the fuse. Their's also a resistor on some units next to the fan that can bake kind of a white cylinder. So you have to check continuity. I would also jumper power to the fan to see if it works. For the relay I usually reach into my bucket of relays and try another one so maybe someone else can help you with this.

4BTA 3.9 Cummins Stepvan
86TD Golf
91TD Jetta

[VWCaddy]

The hot water trick works well for the thermoswitch and also for testing thermostats, which I do before installing a new one.

For the relay, assuming you have one, a couple of simple tests can be done. With the jumper for the thermoswitch connector, see if you can either touch or listen to the fan relay when the jumper is inserted or removed. If you feel or hear a click from that relay, then that means the relay's coil is working. If no click is heard, then the coil may be burned out. If you hear/feel the click but the fan does not run, try pulling the relay and inserting a jumper across the power terminals of the socket, for a typical Bosch type relay, 30 is usually the power source and 87 is the output contact. If the fan runs with the jumper, that says the wiring is OK and the relay contacts are toast. Two options, one is to pop of the relay cover and use a small file to clean up the contacts (they may just be dirty). Or it that fails, then a replacement relay is called for.

[BlueDog]

Okay, I did all the things that were suggested. Found the wiring was good, so was the relay. Fan would come on just fine when I jumpered it. Put the thermoswitch in water and heated it and found it was not working. I had another used one on another radiator. Check it in the hot water and found it worked. After installing it everything works like it should and this step by step exercise helped me understand the whole thing better too. I sure appreciate the help. Thanks!
Next thing to get working is the fuel gauge.

[Fatmobile]

Glad to hear you got it working.
While you have it all fresh in your head, you might want to wire in a manual rad fan switch so if the "new" thermoswitch dies in rush hour traffic (that's when it happens to me) you can just flip the switch and laugh at your car's feable attempt to mess with your day.
Not that you'd ever sell your car but it's a nice upgrade that increases the resale value.

[VWCaddy]

Yep, easy to add a switch is you have the fan relay:
- http://www.4crawler.com/Diesel/CheapTri ... rFan.shtml