can anyone tell me if their is a way to tell if a sending unit is bad? this is for an electric fan thanks:confused:

Stick it in a cup of boiling hot coffee (or water) and measure the switch to see if it opens or closes (changes state while using the OHM setting).

allright I'll give it a shot, thanks Big Dave

The biggest mistake made when installing the switch is putting teflon tape on the threads. The tape prevents the the switch from completing the ground path when it closes. As a result the relay never closes and the fans do not run. If the switch is out test it to be sure it is good.

This also is true for the installation of water temp senders for electric guages.

i cleaned the threads and put it back in the intake manifold then let the engine heat up to 220 degrees an put an ohm meter on it and no change in ohms. so im guessing its the sender, Ive changed relays and its a painless wiring relay so each wire is labeled. I think i'll buy a different sending unit this time as this one is a painless and its only got about 5k miles on it for $36 bucks you would think it would last longer. alright enough whining, thanks for the help guys.

Where did you connect the leads? One should be on the terminal and the other to the body of the switch. If you had a 0 ohms reading at temp then switch would have been closed, if no reading at all like cold then it is not working. it is better to check cold for an open circuit and then place in a pan with enough water to cover the up to the threads and bring to a boil and then test. In the manifold the heat can not be controlled as well as a pan of water.
Be aware that some switches do not close at a reasonable temp. My sons 94 Firebird with the LT1 does not turn the fans on until 230 degrees. I am using this switch (http://www.ecklers.com/product.asp?pf_id=40290&dept_id=1748) in the El Camino.
They are available in 4 different temp ranges I am using 40290 and have tried 40416 but the fans ran all the time. My thermostat is a 180 degree Robertshaw brand.
40415 on at 185..off at 170
40414 on at 170..off at 155
40416 on at 195..off at 180
40290 on at 200..off at 185

Philip thanks for the info, I noticed when I was removing the sender that water didn't just flow out got a lot of air so I decided to bleed the system. Sure enough had a bunch of air in it so after a couple times of letting the car heat up with the radiator cap loose and adding a little water the fan started working properly after I got the air out . thanks again for all the help guys:hurray: