JD 4600 temperature goes in the red within a minute or so running from cold.

[oldpilgrim]

thermostat.

 

[Gary Fowler]

I second a sticking thermostat. REPLACE it and see how it works.

 

[dfkrug]

And bolting a temp gauge on top of the console would look really stupid.

Not really. If the temp, fuel, or hour meters go bad, I suggest doing exactly that, as I did
on one of my 4300s. Lots of room on the left side.

I have been inside the cluster, checking for bad contacts and cold solder joints.

I am #4 for checking the thermostat. You can boil it in a pot of water to test, and buy a
replacement at your local auto parts store.

 

[zaschf]

I've measured the resistance of the sensor at the console (connector) end and it doesn't appear the have a short...

Cheers,
Frits.

 

[klcoble]

Frits, I know what your going through! My 4600 does pretty much the same thing. Cranking from cold it quickly pegs the gauge, and know it's not a blockage nor a short to ground on the gauge wire. I just replaced my sending unit tonight. "didn't fix the issue". Taking the sending wire and grounding to the block gives same result, but once the wire is removed gauge goes back to cold. I guess the issue is in the gauge itself. I'm sure there is all kinds of dirt and debris that have worked its way into the gauge itself. Just a thought. I'm kind of at a loss.

 

[zaschf]

What I'm going to try is a variable resistor (0-1000ohm) in series and work out a nice midpoint on the gauge. Once I know the resistor value I'll put a fixed resistor in and Bob is yer uncle.
I did blow out the console and the gauge and I did check all the solder points on the pcb related to the gauge but couldn't find anything wrong.

I'll let you know how I get on once the rain stops

Cheers,
Frits.

 

[kuboman]

My money is on the guage. One more thing to try is to do a direct ground from the sending unit to the gauge if that is possible. Bad grounds will do crazy stuff with electrics.

 

[zaschf]

Good point, but if there is a bad ground on the engine wouldn't the starter motor not struggling?

 

[kuboman]

Good point, but if there is a bad ground on the engine wouldn't the starter motor not struggling?

Likely, the most likely place for a bad ground is at your instrument panel. If you could get a perfect ground right at your gauge then you could confirm or eliminate one possible problem.

 

[zaschf]

I'll try that right away.
...
Well,
tested it and no difference in the reading.
I also checked the instruments voltage and it's exactly 12V with the alternator sitting at 14.4V.
Looks like the voltage regulator is working just fine.

I've recorded the following measurements:
Sensor resistance at cold (20DegC) 1100 Ω.
Sensor resistance at working temp(+/-80DegC) 147 Ω.

Gauge readings:
The gauge reads high with a test resistor of 300 Ω or less.
The gauge reads mid scale with a test resistor of 650 Ω.
The gauge reads cold with a test resistor of 1000Ω or higher.

Since the gauge is not easily replaceable a simple solution would be a sensor with a working temp(+/-80DegC) resistance of 650Ω.

The hunt is on...