Coolant Temp gauge problems...

[XonDubs]

Ok here goes nothing.

When I first purchased my 97 Limited 5.0 AWD it had a 5-speed cluster in it, and the temp sending unit for the gauge was unplugged. When you plug it in, it makes it's way to the red(about when it should be fully warmed up the needle is almost touching the white line before the red, right about when the check gauges light comes on is where it stops). It rises slowly like it would otherwise, but is way off. Right away when you start it, the needle is about 1/16-1/8 inch from the cold line. I changed out thermostat, lower radiator hose, radiator(was leaking a tiny bit anyways), radiator cap, and the sending unit, with no change. I even changed the sending unit with another 2 new ones just to make sure it wasn't bad out of the box.

Took it into this shop who ran a scan tool on it, as well as used the infrared thermometer. They verified that it only gets up to operating temp(190-210 i don't remember the exact number) but no hotter, so they chalked it up as the 5-speed cluster being the culprit.

So Yesterday I went and purchased a cluster for an auto(coincidentally from the identical explorer in the junk yard lol) Installed it, and there was no change whats so ever. So I did a search on yahoo, and the forums. And came up with most of my answers being bad ground. So I replaced the ground wire that goes from the batt to the body. Cleaned up the metal connections, checked all grounds(that I could see anyways)
Start it up, and get no change at all.

So now here I am, stumped. Don't know what else it could be short of the actual wire its self.

So here is my question. Does that wire go straight from the sending unit to the cluster? Or does it go into some sort of body module first?
I know the 2 wire temp sensor goes to the ECU but this one shouldn't.

Do you guys have any ideas for what else it could possibly be?

I think if it is not that wire then, my only other option would have to be they gave me the wrong sending unit every time(slim chance but it could happen)

If all else fails what size resistor would I put in line to make it read more accurate?


Thanks in advance.
-Nick.

 

[Dilbert5]

Ok first off, it appears that the sensor goes to both the message center, and the instrument panel. So something in the message center could be causing a problem.

I looked up the values of the sending unit, It should read app 300 ohms when cold. 45 ohms at 1/4 to midway on the temp gauge. and 18 ohms hot. Do you have a DVM so that you could check the sensor? Or you could buy some resistors from radio shack to check the function of the gauge.

 

[XonDubs]

Ok first off, it appears that the sensor goes to both the message center, and the instrument panel. So something in the message center could be causing a problem.

I looked up the values of the sending unit, It should read app 300 ohms when cold. 45 ohms at 1/4 to midway on the temp gauge. and 18 ohms hot. Do you have a DVM so that you could check the sensor? Or you could buy some resistors from radio shack to check the function of the gauge.

Are you sure? Because the message center reads "coolant temp ok" even when the sending unit is unplugged. And when it is plugged in and the "check gauge" light comes on the message center still says "engine temp ok". I was pretty sure the sensor goes to both the ECU and the message center, and the sending unit went to just the cluster on the dash.

Were you talking about the 2 wire one or the 1 wire one?

And the sending unit was tested at the shop it was at, and they said it was in range.

 

[Dilbert5]

According to the ALLDATA manual, the single wire sensor goes to the message center, and the instrument panel. The 2 wire is to the ECU only. I would suggest buying a couple resistors from radio shack and use them to check the gauge function.

 

[XonDubs]

So this wire goes directly from the sending unit to the message center/cluster then? or does it go through some sort of body control module first?

And thanks for looking into this, and helping me out.

 

[Dilbert5]

according the the schematic, there is a single red / w white strip wire going from the sender, thru a connector, and then to a splice. One of those wires goes to the dash gauge, the other goes to the message center.

 

[XonDubs]

according the the schematic, there is a single red / w white strip wire going from the sender, thru a connector, and then to a splice. One of those wires goes to the dash gauge, the other goes to the message center.

Does the schemadic show by any chance where the connector and splice would be located at?

 

[Dilbert5]

I searched both Alldata, and Mitchell on demand, they both agree that the connector (c148), is located on LH rear corner of engine compartment. The splice s276 is listed in both schmatics, but they do not say where it is physcially located. They both agree that it is electrically located between c148 and the instrument panel. I would guess that it is located behind the instrument panel.

 

[XonDubs]

Thanks! you were a big help for me. I'mma check all the connections this weekend and the wire. I wonder why the info center says engine temp ok even when unplugged tho thats weird. So in reality the cluster is fed directly off the sending unit(well it is spliced but otherwise yeah) so it HAS to be the wire, we've changed everything else lol

 

[Dilbert5]

It is possible that the message center itself is corrupting the signal. I suggest unplugging the message center and see if it instrument panel gauge reads normal, then check the connector (since it is in the rear of the engine compartment, it could have been damaged). it is the red, with white strip. The splice is also possiblity.

If it is still acting up, my next suggestion would be to unplug the instrument panel, and message center, and sending unit. Ohm the harness to ground (with everything unplug you should see very high resistance, (in meg ohms, or open). Then plug the sender in, and measure the resistance to ground 1) at the sender 2) at the instrument panel 3) at the message center. They should all be the same

It sounds like there may be a problem with the harness itself, generally there are two common problems 1) harness chaffing on metal parts (generally the result of missing clips that allow the harness to lay on things that it should not). 2) there could have been a short that damaged some wires (this is extra hard to find if it is internal in the harness.) a short could add another signal path that it should not have.

So anyways, by unhooking everything, and ohming to ground, and the other tests I described, I think we could eliminate any problems with the harness. Good luck