testing temp gauge

[Briana03]

Hello & WELCOME to TractorByNet.com!

I have moved your thread to the New Holland Owning/Operating Forum. You'll get a better response there.

 

[JC-jetro]

If it is electric, just pull the wire off the sending unit and ground it with the key on and if the guage moves all the way to the other side the guage and wire are ok. It would have to be the sending unit.

That is a good test. It tells you much but not all. It does not show if the gauge is within calibration point or not. The sender unit's resistance varies with temp. Warmer then less resistance (ohms) and colder more. For the sake of compassion only, The sender on my tractor reports 690 ohm cold, 140 ohms @ T-housing temp of 172 and 92 ohms 1/8" on the right side of the middle @ 196 degrees Fahrenheit. Obviously needle pegs out when grounded against the body and the resistance of almost zero ohms. The OP might be able to find the resistance spec to check against but still he'll need temp reading best achieved by non-contact infra-red thermometer.


Welcome to TBN Blue,

JC,

 

[jinman]

That is a good test. It tells you much but not all. It does not show if the gauge is within calibration point or not. The sender unit's resistance varies with temp. Warmer then less resistance (ohms) and colder more.

JC, there are two sending units listed for the 1720. One is a switch for a temperature idiot light and the other is a thermal sensor as you've described. Twoone needs to give us some details of his tractor. Has he had this since new? Is there a chance somebody put in a switch when he needs a sensor? Perhaps his instrument panel was replaced with the wrong one and the sensor is just not compatible. Since he said it has two wires, it makes me think it is a switch for a light and not a thermal sensor. Folks have suggested a non-contact IR thermometer and that would be great. He also may be the victim of a faulty thermostat. He needs to help us to help him by giving more info and maybe even a picture would be nice.:thumbsup:

 

[twoone]

Thank you all BRI for moving me thanks to JC-eto and to thanks to Jin man. am not sure as to what information you need to know about the tractor however there are two wires going to the sensor and the sensor has to terminals the tractor has a gauge , it was bought in 1993 from our local dealer Woodland Ford. it was a used lease with 200 hours. I might note that I have never had a visible over heat and for the life of me I can't remember if it ever worked until my son noticed that it wasn't moving.As yet I haven't had a chance to check any thing out as yet just lots to do right now but will try by the end of next week. Am wondering now if something was switched however the wiring is there?.Again thanks for all your input we will lick this thing. Paul:thumbsup:

 

[JC-jetro]

Thank you all BRI for moving me thanks to JC-eto and to thanks to Jin man. am not sure as to what information you need to know about the tractor however there are two wires going to the sensor and the sensor has to terminals the tractor has a gauge , it was bought in 1993 from our local dealer Woodland Ford. it was a used lease with 200 hours. I might note that I have never had a visible over heat and for the life of me I can't remember if it ever worked until my son noticed that it wasn't moving.As yet I haven't had a chance to check any thing out as yet just lots to do right now but will try by the end of next week. Am wondering now if something was switched however the wiring is there?.Again thanks for all your input we will lick this thing. Paul:thumbsup:

Paul,

As Jim indicated unbeknownst to me having possibility of digital (idiot light) temp sending unit. The one I pictured below is an analog most commonly used on tractors or older cars. You see it close to t-stat housing and one wire coming out of it.



The "idiot Light" has a different test procedure. With a digital (in a way) switch, you have two states. first state is the normal state (contact on or off) with assistance of a little spring or bi-metal to break or make the contact. second state is the other extreme like really hot engine.You can take the sender unit out and either use a test light or ohm meter. on one state the test light will illuminate and is off on the change of state. What you're looking for is a change of state when you go from cold to hot. You can simulate the hot condition by partially submerge the sending unit in the boiling water. if you have digital light, then is it always off or on? Do you know if your light is burned out. I myself like to have analog with an idiot light for backup... I think I'd even extra back up using a horn so If the tractor idling hot it would squeal.

JC,

 

[jinman]

JC, if it is the light type (two wire) then he should be able to jumper the two wires together to simulate a closed switch and look for a light on the instrument panel when the key is ON.

BTW: I'm saying 2-wire because that's what twoone says the sensor has. That seems very wrong from everything I can find, but if he says it has two wires, then I'll believe him. However, the TC45A (non-deluxe) has a light and the TC45D has a gage. Both of these use a part numbered sensor that is the same as the one used on the 1720 according to the parts list. On both of those gages, there is only one wire going to the sensor. The switch just grounds the wire and the sensor is a thermal resistor to ground. I'm baffled by twoone having two wires and without insulting him, I wonder if he may be mistaken and not on the temperature probe. That's why I was hoping for a picture.

 

[JC-jetro]

JC, if it is the light type (two wire) then he should be able to jumper the two wires together to simulate a closed switch and look for a light on the instrument panel when the key is ON.

BTW: I'm saying 2-wire because that's what twoone says the sensor has. That seems very wrong from everything I can find, but if he says it has two wires, then I'll believe him. However, the TC45A (non-deluxe) has a light and the TC45D has a gage. Both of these use a part numbered sensor that is the same as the one used on the 1720 according to the parts list. On both of those gages, there is only one wire going to the sensor. The switch just grounds the wire and the sensor is a thermal resistor to ground. I'm baffled by twoone having two wires and without insulting him, I wonder if he may be mistaken and not on the temperature probe. That's why I was hoping for a picture.

Thanks for clarification Jim and as always you are thorough. I suppose we provided enough information as to general nature of question asked. Paul just needs to verify what he has and use the general info provided.

JC,

 

[twoone]

stand by am confused right now and may be looking at a different sensor according to the picture you all sent, I just got a cheap shop manual am going to look at it myself and get right back to you all.

 

[twoone]

OK" here what I found out and thanks to your picture I really feel stupid I was working on a sensor on the part called case p/n sba145216390 and the sensor their is for the air filter switch p/n sba385200570 I found these numbers on the web at a parts suppler however they do not show the picture for the temp sensor and location very clear. I looked the tractor and it is as your picture shows and with the single wire. now we will gnd the wire and see if the gauge moves need to get another person to observe so will do so asap. now my operators manual also shows that I have a coolant level warning light to the right of the oil press gauge, and I could find nothing about the wiring it. left a ? the tractor has a temp gauge as well located located below the air cleaner warning light, the tractor s/n is UL 32835. I hope what I have done and is the information you ask for ????? what do you guys think at this point.? thanks again for your help. Paul

 

[jinman]

Paul, I think we are off the detour and back on track.:thumbsup: Ground that wire going to the sensor and see what your gage does. If it goes up, then you can be fairly sure it is working properly. You can attach an alligator clip jumper to that wire and to ground, then go turn on your key for a few seconds. That way you don't need a helper.

Next, you'll need to check the resistance of the sensor to ground. Do you have a multimeter and know how to read resistance? JC may know for sure what the resistance in ohms should be for a cold engine.

The final thing is to pull the cover that attaches to your upper radiator hose at the engine where your thermostat is located to see if the thermostat is faulty. Frankly, I think I'd stop by Harbor Freight and pick up one of their cheap infra-red non-contact thermometers. The small ones are normally around $10 and well worth every penny. You'll find tons of uses for it besides just checking your radiator's temperature.

Also, if your radiator never gets very hot during operation, that's a clue that the thermostat is stuck open.