96 B2300 Temp Gauge Diagnostics.

[Nezorf]

Coolant Temperature Gauge

I have a dead temp gauge. I have great heat, enough that I'm sweating in the cab. As I've had some vehicles die on me from overheating I'm over cautious and am running the heat at full blast when I drive. I haven't driven it further than 20 miles yet so its not too worrysome.

I started a new job today and will now have to drive my truck to and fro during rush hour. The idling on the hot highway has got me worried so the temp gauge has moved up the priority list.


-I pulled out the cluster and ensured that the connections were good. It takes about 15 min, and is pretty damn easy. The hardest part is fining all the bolts and getting the cluster past the steering wheel.
-I removed the gauge and bench tested by crossing a mostly dead AA battery between the terminals and it shot up to hot
-Dug around the engine and found the coolant thermostat control for the computer (two wires) its on the top front of the engine right near the main coolant hose.
-Also found the Temperature sending unit (in the photos). Grounded that out and the gauge didn't move.

Next steps.
-Because I got the gauge to jump up, I'm thinking there is a short somewhere in the wiring. I'm probably going to pull the cluster out again and test the gauge again just to be sure.

7 months later:

I've been busy with other things around my house and have neglected my truck until recently.

I've been screwing around with the temp gauges for a while and have been thoroughly confused.

My temp sending unit reads good numbers from pole to ground.
The two gauges I have move around when a 9v is crossed on the poles.
I get consistent numbers when I drive the truck with a multimeter attached to the socket.
The gauge doesn't budge when I ground the wire going to the sending unit.

There are three poles on the temp gauges that plug into three sockets.

1 2

3

1=ground

When I connect a 9v from 1-3 on the gauge it pegs to C
When I connect a 9v from 3-2 on the gauge it pegs to H

I have two gauges, one has a resistor from 2-3.
If the gauge with a resistor is plugged in, it sits below C and jumps up to C when the key is turned.
The gauge without the resistor sits below c and jumps up to dead middle of normal when the key is turned.

While driving if I connect a multimeter from 1-3 it shows 14.xx V
While driving if I connect a multimeter from 1-2 it shows .223 cold and goes up to .311 on my 10 mile drive.


I am in no way concerned with aesthetics or specific temperatures, I just cant afford to have this overheat.
It runs great, the upper hoses are hot when they should be, the heat is great (though the blower is wimpy) so I'm not too concerned about the engine but I still don't like driving too long not knowing its temp.

Since nothing happens when i ground the wire to the engine, i'm assuming its in the wiring and up
Since i see V's in the cluster I'm assuming its in the gauge.
Since i can peg the gauges with batteries, I'm assuming they are good
Kinda at my wits end for what is going on with this.

So my questions are:

-Any idea of what else I should replace/check first?
-Can i even test it with a multimeter this way?
-Is there anything aftermarket that I can toss in there/wire in that will work?
-If there is a wire fault, how easy is it to run a spare wire, and where does it go to. Should run it right to the wire harness behind the dash or straight to the cluster?

It says .297 on the multimeter
P.S. my passenger took this. Not that stupid.

 

[Explorin94]

The best way to say this is......the sender connects to the gage which is merely a switch. I would dump the factory sender for a good mechanical sender and be done with it.

As for parameteres on where the dash should read I don't think has ever been brought up here. We have always told others to simply ground the wire that goes to the block sender and see if the gage goes up. The dash gage works off of ground resistance supplied by the block sender.

 

[Nezorf]

Thanks for the reply!

Any suggestions on what brand of sender to get?
Don't need anything fancy.

 

[Crossthreader]

From what you have said so far, it seems like the wire from gauge to sender may be open. Try to check for continuity between gauge term 2 and the sender end of the wire. If it shows continuity, then check to see if it is grounded when both ends are disconnected. It should show zero resistance end to end and infinite resistance to ground when disconnected. Since you will be in there with your meter, measure the resistance of the sender to ground. The manual I have gives 275 ohms cold and 16 ohms hot as values for the sender. This should let you narrow things down a bit.

Paul

 

[RonD]

Yes the dash temp gauge circuit is a pretty simple circuit.

There are two temp sensors on EFI engines, a 2 wire and a 1 wire sensor, the 2 wire temp sensor, also called the ECT, is for the PCM, it is in essence the "choke", it tells the PCM to run engine rich until it warms up.

The 1 wire sensor uses the engine as the ground, and the 1 wire just runs back to the dash gauge, the sensor itself is just a heat sensitive resistor as it warms up it has less resistance.
So if you have the key on the gauge gets 12vDC but if sensor is cold there is too much resistance for a ground so needle stays down, as engine warms current starts to flow as resistance is less, needle rises.
As said in previous post, if key is on you can disconnect this 1 wire from the sensor and connect it to any ground, needle should go all the way to the top, 0 resistance.

If it doesn't then I might just run a new wire from sensor to dash gauge, finding a broken wire can be a pain.

The oil pressure gauge sending unit on Fords is the one that is a switch, on/off, temp sensor for gauge is a resistance type sensor.

The regular sensor available at any auto parts store is fine to use if that's where the problem is, never use teflon tape on 1 wire sensor, it prevents good ground.
Nothing special about it and no "better" one than another, unless you are partial to OEM.