Water Temp Gauge Problem

[dlsmith]

A couple of months ago, I was mowing the lawn and looked down at the gauges and the temp gauge was clear up in the middle of the hot zone. I throttled the engine back and headed to the shop to check it out and while I was looking at the gauge, it suddenly jumped back into the middle of the range where it normally runs. I continued mowing and it would do the same thing every few minutes. I suspected the temp sensor, of I got one from the local dealer and replaced it. However, the problem persists.
The needle jumps instantly, so I know the engine temp isn't changing that fast, and my infrared temp gun shows it running around 180F.
I removed the wires from both gauges, cleaned them and reinstalled them, but it didn't fix the problem.
Looking at the wiring diagram, the fuel gauge shares power and ground connections, but it doesn't exhibit the same behavior, so I doubt that is the problem.

Could it be the gauge?

 

[North Idaho Wolfman]

Have you pulled the radiator cap off ( not the overflow) and checked the level in the radiator, as low fluid level will cause the gauge to do that.

 

[dlsmith]

Yep, it's full and the reservoir is half full.

As I said, it can't be the actual water temp fluctuating that fast, it would take at least a few seconds for the sensor itself to cool off or heat up. This happens in an instant.

 

[Roadworthy]

Some automotive gauges have a voltage regulator which drops the vehicle voltage from twelve volts down to about five volts for the gauge. Try to find a wiring diagram for your specific model to see how the gauge is fed.

 

[Dave_eng]

The use of a voltage regulator specifically for the instruments is not current design on Kubota's.

The test for the meter itself is to remove the wire at the sensor and check for battery voltage.

The sensor is just a resistor whose Ohm value changes with temperature so you will need a cheap multi meter to check its values at various engine temperatures. See attached.

If the wire to the sensor is chaffed and touching a ground path, this would produce rapid swings in the temperature gauge. Double check that the sensor is not loose in the engine block.

Dave

 

[kubotasam]

I bought a B7500 a couple of years ago. When I first started using it, it showed very similar symptoms. Turned out to be corrosion where the wiring harness connected to the guage cluster. Never worked on a BX so don't know if your tractor has similar connection.

 

[dlsmith]

The use of a voltage regulator specifically for the instruments is not current design on Kubota's.

The test for the meter itself is to remove the wire at the sensor and check for battery voltage.

The sensor is just a resistor whose Ohm value changes with temperature so you will need a cheap multi meter to check its values at various engine temperatures. See attached.

If the wire to the sensor is chaffed and touching a ground path, this would produce rapid swings in the temperature gauge. Double check that the sensor is not loose in the engine block.

Dave

I saw that test in the WSM and am going to do it this weekend. I also see in the wiring diagram that it connects to the voltage regulator, so I'll pull that connector apart and make sure the connections are clean and making a good connection.

Thanks.

 

[dlsmith]

I bought a B7500 a couple of years ago. When I first started using it, it showed very similar symptoms. Turned out to be corrosion where the wiring harness connected to the guage cluster. Never worked on a BX so don't know if your tractor has similar connection.

There is not cluster on the BXs, the harness wires connect directly to the gauges. But as I mentions in the previous message, I will check the connection on the regulator connector.

I'll report back with what I find.

 

[dlsmith]

Problem fixed.

A couple of weeks ago I changed the temp sensor on the engine, went out and mowed the lawn, and the temp gauge was still doing the same thing. It would be at about mid-scale then occasionally jump up to the top of the hot range, then after a few seconds drop back to mid-scale.
I did the trouble shooting procedure spelled out in the WSM, and it checked out okay. So I ordered a new gauge from Messicks and installed it last weekend. Today when I mowed the lawn, once it was warmed up, the needle stayed at about 1/4 of the way up on the scale, and never moved from there.

So, apparently it was a bad gauge, which is what I thought it was from the start.

 

[Dave_eng]

Problem fixed.

A couple of weeks ago I changed the temp sensor on the engine, went out and mowed the lawn, and the temp gauge was still doing the same thing. It would be at about mid-scale then occasionally jump up to the top of the hot range, then after a few seconds drop back to mid-scale.
I did the trouble shooting procedure spelled out in the WSM, and it checked out okay. So I ordered a new gauge from Messicks and installed it last weekend. Today when I mowed the lawn, once it was warmed up, the needle stayed at about 1/4 of the way up on the scale, and never moved from there.

So, apparently it was a bad gauge, which is what I thought it was from the start.

Thanks for the final chapter update.

Dave