View Full Version : Adding a factory-type Temp gauge and 3-wire Coolant Temp Sensor...

01-27-2008, 04:57 AM
I've been working on my 1984 Century project car today. It had a sorry cluster with only a speedometer and gas gauge. I had this cluster with voltmeter, temp gauge, gas and speedometer. The speedometer was bad so I installed the good one from the cluster that came in the car. I posted about it this morning already.

The clusters are physically interchangable however the wiring is totally different. All wires had to be re-pinned in the connectors. Thankfully, only 3 wires had to re-pin from the left to right connector! Those required extending the wires. This is how it looks after the rewiring:

Below is the wiring changes to be made, click to see it.

Next problem was where to put the sender for the gauge. My 1986 Century has the sender in the rear bank cylinder head. There is a 3/8 plug in that area on the 60° motor but this car's Buick V6 does not have any remaining unoccupied sensor ports. I found the solution on 60°V6.com. It's the 1996 and newer 3-wire sensor. This sensor has a standard-size body with a 3/8 pipe thread. It contains both an isolated 2-wire sensing element for the ECM, and a ground-referenced one-wire sensing element for the panel gauge. The ECM sensor element has the same resistance characteristics as the original 2-wire sensor, but I was not sure about the instrument panel sender. Was worth a try, though! This is the original 2-wire ECM sensor, installed in a tee because there are no more available ports in the engine:

This is the new 3-wire unit, showing the connector and the plug for it:

Here I have made up a harness and plugged it into the 3-wire sensor. The 2-pin wetherpack is the ECM's side, and the 1-pin is for the gauge cluster:

The end result is a nice, clean install with no clutter. Hard to tell the difference from the original 2-wire sensor.

And the burning question is answered by Ease Diagnosis...

So now I have a temperature gauge! The part number of that 3-wire sensor is GM#10096181 I don't have the number for the mating connector but it is a standard MetriPack connector I use at work for pressure transducers. Many parts places have it, it fits this and TPS sensors, too.

Three-wire CTS Pinout:
A- ECM sensor
B- ECM Sensor
C- Panel gauge sender

Hope this inerests ya!

01-27-2008, 06:41 AM
sweet. thats killer. Sooooo....I wonder if you could replace the sensor at the bottom of the waterneck that runs the ecm with one of those, abandon the sensor that reads inaccuratly in the cylinder head for the guage , and plug in its pigtail into the other wire on the new sensor. Two devices being fed from the same place and sending the same info.

01-27-2008, 02:48 PM
Don't see why it wouldn't work for your car too. The sensor is a standard GM part for any GM ECM. I DO know the Delco ECM's all use the same sensor resistances. I do NOT for sure know that all instrument panels use the same sender resistance. The 3-wire sensor is factory fitted on a 1996 Grand Prix. (and other cars)

The water neck is a mediocre place for an overheat warning sensor, if this is your one and only warning sensor. The tee fitting on my engine is a horrible place for a warning sensor. I do have a warning lamp sensor directly in the engine in a nother location so I don't feel too unsafe this way.

I have been told in engine classes at work about the proper placement of a gauge or warning sensor. It makes sense to me, too. It is always desirable to have the gauge or warning sensor mounted directly into the cylinder head.

This is because it will measure cylinder head temperature in the case the coolant is all lost at once with the engine running. If the sensor is in the water outlet or some remote location it depends on coolant FLOW to bring it a constant sample of engine-temperature coolant to measure. In this case if all coolant is lost, it will not react to the overheating engine before damage is done. In other words, by the time the water neck heats up to the
warning threshhold, the cylinder walls and heads (at the heat source) are already damaged.

Now, if the gauge or warning sensor is in the cylinder head, and all coolant is lost, it will react immediately. The head will begin to overheat and the metal into which the sensor is mounted will transfer heat to the threaded housing of the sensor, and that brass housing will transfer heat to the tip of the sensor where the reading is taken. You will be warned in
time to shut it down.

I tried to follow this on my Buick Turbo (shown here) but it has NO sensor ports in the cylinder heads. The warning lamp switch is in the manifold lowest and closest to the head. The 3-wire sensor for the ECM and gauge is in the heater outlet hose (this car has constant flow to heater core) and the electric fan switch is in the manifold in a higher location.

If the engine looses all coolant, I want as early of a warning as possible. It doesn't matter about the ECM (on this car) getting a rapid response in the case of total coolant loss. The first most important thing is to warn the driver to allow a safe shutdown before engine failure. Some later model cars use the ECM to drive the overheat warning light and therefore the ECM sensor is also the warning sensor.

Some early 90's BMW's had this problem from the factory. If you blew a hose, it would melt holes in the head before the gauge went into the red. Had to replace 2 heads that the drivers insisted it NEVER went into the red, but after the engine started to fail and they pulled over, it was obvious the engine was about on fire.

01-27-2008, 04:39 PM
errr..................so it looks like i have to do work to do a swaps............thats sad. oh well great job any ways. it looks nice

01-27-2008, 05:26 PM
I thought all the diesels had a temp gauge. Guess I'm wrong?

The wiring diagram worked out OK except one ground was bad in the car's harness. After I fixed that everything worked.


01-27-2008, 10:21 PM
David, your temp guage location theory is all good except that on these 60 degree motors you can get a false reading in the head. The guage will read hotter than it actually is because of the design of the head. There is a "dead" spot where the sensor goes. Poor coolant circulation in that area. You can get a more accurate, balanced reading of whats going on in both heads from the water neck area. Thats where the ecm is getting its readings from anyway.
I know its overkill, but 3 temp guages, one in the left head, one in the right, and one at the neck would give the best readings. It would be interesting to see, but a pita to do!

01-27-2008, 10:47 PM
You are correct about the high reading in the head. It does show a little hotter than the ECM data but still stays in the normal range of the gauge. On the Century cluster, 220 is straight-up on the gauge, and it never goes above that unless the fan is not working or there is another problem.

There _MAY_ be a difference in this dead spot in the iron head vs. aluminum head engines, mine is iron. My turbo 60° motor has never had a chronic overheating problem, real or imagined.

The 3-gauge idea would be interesting. My TechEdge datalogger could do 3 or more sensors at the same time. As if I don't have enough projects already! :)

Before I went MPFI / Turbo on this motor, the sender was in the thermostat housing. I had a heater hose pop off while I was in a store. I started the engine and left with no coolant in the engine. About 2 or 3 minutes later, I hear pinging in the engine, look down and the gauge is in the normal area.

Knowing there was something wrong (due to the pinging and power loss) I pulled off, stopped the engine and opened the hood. As I was pulling over, the gauge was at 3/4 scale (high normal). Been driving at 65 MPH for 4 to 5 minutes w/o coolant.

I saw what happened but the engine was too hot to work on. It was smoking from all over and I could feel heat radiating so I sat down in the car waiting for it to cool off. When I turned the key back ON (without starting), the gauge was over past 280.

Over the next minute it went so far past 280 that the needle was not visible in the instrument panel!!!

This episode damaged the engine and it had piston slap (knocking) from that point until the rebuild and turbo install.

After this I moved the sensor to the rear head and it has worked better since that. One time the lower radiator hose blew off, and it immediately responded and hit 250 by the time I stopped (less than a mile) Never went off-scale after shutdown, maybe hit 280 before it started cooling off.

In my opinion; the water outlet where you get a better true reading from both banks, it is the place for the ECM sensor. But for fastest response in abnormal operating conditioins, the heads are a safer location for the warning sensor.

If you had a dummy light and a gauge, you might put the dummy light switch in the head and the gauge sender in the water outlet with the ECM sensor?

Interesting points!


01-28-2008, 01:26 AM
Nice! I didn't know a three wire coolant sensor worked with our ECMs/ clusters

01-28-2008, 02:18 AM
Neither did I until I tried it and measured the results! Live and learn!

If anyone wants a temp vs. resistance table for the panel gauge side of this sensor, I can post it. Goes from 44 to 215°F but will give you an idea if yours is close.


02-28-2008, 01:01 AM
I just got my new oil pressure gauge sensor in. I put in a new temp sensor too, but it turns out it was the exact same sensor that I had in before! I got another sensor, also supposedly for a gauge, but the connector is round with one metal connection. The sensor on my 3.3 v6 has an oval connector with two metal connections. :tear: Do I actually have the right sensor? Because the thread seems larger than it should in diameter! Does it go somewhere else? I sure can't find a round connector for another temp sensor anywhere. My factory service manual and haynes are actually leaving me hanging for once! :help:

02-28-2008, 03:01 AM
There is a temp SENSOR (note the spelling) with an oval 2-pin connector. It should have a black and a yellow wire. This is for the ECM and has nothing to do with the gauges.

There is a temp switch used for cooling fans. You car should not have this. It has a round "mushroom shaped" connecor with one teminal inside.

There is a temp switch for an idiot light that has a square /rectangle connector with one wire.

There is a temp sender (note spelling) for the gauge, which usually has one flat terminal.

It's easy to tell a gauge sender from a warning light switch. Use an digital ohm meter, and measure from the threaded base of the device to the terminal. A warning light switch will show "OL" and this reading will not change. A gauge sender will show resistance, that will be slowly decreasing as the sender responds to your heat as you hold it.

In a nutshell: If you get "OL" it is a light switch; if you get "numbers" it is a gauge sender.

Hope this helps! The following list is not all inclusive and only inclused items I have used on my projects.:)


Ps- all the pictures I have posted in the past are not showing beccause the telco lost my static IP address when the power company trenched the line in half. :(

02-28-2008, 03:39 AM
As far as sensor, the one that was on my engine looks like the pic you posted on the bottom right. Oval connection, check.

Now, concerning the gauge 'switch' (?) it most closely resembles the center bottom picture, with a black plastic "cup" surrounding the metal connection. I'll see if I can post a picture shortly.

02-28-2008, 03:45 AM
I guess what the dilemma is where exactly I put it. Next to the temperature sensor, there is a 'plugged' hole. It is plugged with a 'plug' (lol) that threads into the space that I believe the gauge switch goes. Problem is, I don't know where the pigtail is that connects to it!

02-28-2008, 04:14 AM
Does your car have a gauge in the cluster that is not connected?

03-02-2008, 02:33 AM
Everything works except the temperature gauge.

03-02-2008, 06:05 PM
Ok - here's a test. Have you tried to disconnect the green wire from the temp switch and ground it? What happens? Does this illuminate a warning lamp, or does it make the gange pointer move?

If the gauge pointer moves, then you have a SWITCH installed in place of a SENDER. Probably an error on the part of the parts store employee who looked it up for you.

If a light illuminates, they you need to search for another green wire in the harness. Does your manual (the one you go to repair the engine) show the wiring diagram for the gauges cluster?


Ps- Looks like my IP address is now fixed. :) Above is the repost of the senders picture since the IP changed again.

03-02-2008, 06:22 PM
According to the 1990 Ciera 3.3L wiring diagram, your warning light is controlled by the engine ECM. The only green wire under the hood going to a temperature sender should be for a gauge sender.

I beleive the warning light signal comes from the ECM on terminal F2.

Try a TU66 sender in place of your existing switch.

If you ground this wire and the gauge moves, you definately need to install the TU66 sender in place of whatever you have in there now.

03-06-2008, 03:46 AM
Okay, a TU66 sender. How will I get a correct connecting plug-in to the switch?