Trans Temp Guage

[clarence]

Gentlemen, I need your sage advice again. I have a 450C loader. All of the gauges work except the trans temp gauge. I've replaced the sending unit in the trans case and the gauge with no luck. The wiring seems simple--there's a hot, ground and sensor terminal on the back of the gauge. When the tractor starts (when it's cold), the temp gauge needle buries all the way to full hot. I suppose it's possible the sending unit is bad even though it's relatively but that's hard to believe. Any thoughts or suggestions? Thanks, Clarence

[Stan Disbrow]

Hi,

The usual way an electric gauge works is to pass a regulated voltage from main power into the gauge, then down the wire to the sender, which is a variable resistor that has less resistance the warmer the sender gets. This makes the gauge read low when cold and high when hot.

If it buries the needle to the hot side when cold, and stays there, then you have a short to ground somewhere along the wire from the gauge to the sender. It may be a short that clears as the temperature of the machine rises, at which time the gauge will suddenly start reading correctly.

If it shows full hot when cold, and drops down as the oil temp rises, then you have the wrong sender installed. There are 'reverse' variable resistors out there that are low resistance when cold, and high resistance when hot. They are far less common, but do exist. To make matters worse, they readily cross fit mechanically (not like they have left-handed threads)....

Stan

[Labparamour]

The manual for my 450B shows for tranny temp sending unit: 200 deg @ 122 +/- 10% ohms.

[clarence]

Thanks guys, I'll give those suggestions a try. I really appreciate your assistance. Clarence