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

[zaschf]

Hello all,

I have a really weird temperature behaviour on my JD 4600.

Some time ago it started to go in the red within minutes from cold start but, as the engine warmed up it was coming back to a 'normal' temperature reading.
Now it goes in the red within minutes from a cold start and stays in the red even though the engine is not even luke warm.
I've replaced the sender which made no difference.

While testing I noticed in the first minute of running that when I turn off the engine but leaving the ignition on, I get a substantial different reading.

Any ideas would be much appreciated.

Cheers,
Frits.

 

[mrmikey]

just a shot in the dark here never having worked on a JD, how is your voltage reading, could the regulator be going bad? I remember some of the older cars used to have a regulator to run the dash gauges, when that went south all the gauges acted funky.....Mike

 

[zaschf]

Thanks for your suggestion, Mike.

The fuel gauge doesn't have any problems....

A bloke next door from use came up with the idea of a bad engine earth strap. A couple of mVolt could already upset the temperature reading.
The temp sensor is a single wire one.

Cheers,
Frits.

 

[mfreund]

You should be able to test the Guage by disconnecting the wire and reading the guage. Then ground the wire and read the guage. One should be full hot and the other full cold. If that works, it is the sender.

 

[DLTTrekkers]

Good advice

 

[zaschf]

Thanks for that, mfreund.

I've already replaced the sender and it did not solve the problem.
What I can't work out is that with the engine just luke warm, like in the first 30 seconds from cranking, the gauge climbs steadily to well past overheating.
I measured the resistance of the sender within a minute of cranking and it still reads over a 1000ohm which it should be when cold.
At 80DegC it's reading around 250ohm which is correct for the stock sender.

I hope it's not the gauge because that means a whole console replacement.
But then, it sometimes comes right after 10, 20, 25 minutes (it's a bit of hit and miss when it comes right) but most of the time it stays in the red.

 

[doxford jim]

What about installing an aftermarket temperature gauge. The sender can be swapped out and the gauge can be added to the consul. Shouldn't be hard to do and probably pretty cheap as well. Just a thought, maybe a gas filled sensor bulb type might be better then you won't get any electrical problems.

 

[zaschf]

Thanks for that, Jim.
I see what you're saying but it's an integrated console which will be pretty difficult to disassemble without causing problems with the other electronics.
I've already had a go at it with the electrical diagrams available to me.
And bolting a temp gauge on top of the console would look really stupid.

 

[Zebrafive]

The wire from the sensor to gauge might have a short to ground, giving the hot reading.

 

[mrmikey]

Any chance you could have a water blockage or an air pocket where the sending unit is, a screwed up thermostat maybe....Mike

 

[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...