The Fordson Tractor Pages Forum

hello all the temperature gauge on me 4000 not working taken the wire off the sender and earthed it and the gauge moves into the red so the gauge works so must be the sender but when i put the wire on the tester i was not getting a constant voltage it fluctuates between 0 and 12 volts should it do this or should it be a constant 12 volt , going to replace the sender anyway but wondered if there was another fault.
thanks wayne

Shergar, sounds like a faulty sender unit. On my 4000 they seem to pack up every 10 years or so. I allways replace the sender unit with a new CNH one.TSG.

thanks TSG , i'am a little worried that she's running a bit hot so i've orderd a new thermostat as well , will replace sender first to see how hot she's getting.
thanks wayne

Did you mean that you was getting a variable voltage at the sender end of the wire? Does your fuel gauge work OK?

Just wondering if the voltage stabaliser behind the dash, was giving you a problem.

yes i was getting variable voltage at the sender end of the wire , when i earth the sender wire the gauge does move into the red so i assume the gauge is working properly , how many volts should i be getting at the sender wire
thanks wayne

You shoujd have 8 to10V at the sensor.

The voltage should only vary when the sensor is in circuit. The sensor is what varies the voltage.

Hi Wayne,

Not knowing what type of gauges are used in your tractor for sure, but given the fact that there is a voltage stabiliser in the circuit diagram they are probably bimetal gauges. These work by heating a bimetal strip with a coil of resistance wire. The more power through the coil the more the strip bends and the more the pointer moves. The voltage stabiliser that was commonly used with these gauges originally were bimetal as well and they worked by heating a bimetal strip until it bent far enough to open a contact, which in turn let the coil cool then closing the contact. The result was a switching on/off voltage that averaged out to about 10 volts. These were in use right through to the 70s.

The varying voltage on the sensor wire would just be indicating that the stabiliser is working properly. The sensors used with these gauges is a variable resistance, typically varying between 40 and 200 ohms. the voltage on the sensor wire is fairly meaningless. If you knew the sensor resistances for cold, mid and hot you could use a resistor box to test the gauge for accuracy, but given that it moves to the red with a short on the sensor wire I would say it is working OK. Just make sure you get a sensor with the right resistance range, this is definately a case of genuine is best as generic parts could be any resistance.

Regards, Frank.

cheers frank
my tractor was first regesterd in 1967 so will probably have bimetal gauges so that explanes the variable voltage at sender wire .
thanks wayne
[img][img]http://farm4.static.flickr.com/3109/4552512200_ff5d7b457a.jpg[/img]
070 by shergar3, on Flickr[/img]