I have completed swapping an LS2 in my 91 Camaro. The piece of information I having trouble finding is regarding the coolant temp sensor for the gauge in the dash.

Currently I have the small LS style 3-wire sensor in the front of the drivers side head which feeds the PCM (not the larger 98 F-Body sensor). The output from the PCM will not work with my factory 91 cluster which seems to be correct from what I read searching the forum.

My questions which I am hoping to get firm clarification on are:
Is there one coolant temp sensor I can use for the PCM and the gauge?
- Is the smaller 3-wire sensor I currently have capable of doing this if I tap into the signal wire at the sensor?

If not I do have a coolant temp sensor for a 98 F-Body, but the thread side is much larger than the head can accommodate. The research I have done shows people drill/tap the cylinder head to accept this sensor.

Is anyone aware of an adapter which will allow me to thread the adapter into the head, and the F-Body sender in the adapter? Thread size for the head and 98 F-Body sensor if anyone knows both?

Open to suggestions on the optimal way to accomplish this, preferably using the one location at the front of the drivers side if possible.

 

Thread size is the same. If you already have a three-prong then just wire up the third and see what happens. If it doesn't work then use a 98 Camaro sensor.

 

Yea I had this same issue, and still kind of do. I also considered drilling the head to fit the much larger third gen sensor, but I ended up using a 98 ls1 sensor. I removed the plug in the rear of the passenger side head, and installed the other sensor there, then wired that to the green third gen temp wire. Being it's a 4th gen sensor, it's not 100% accurate. The gauge reads low maybe 10-15 degrees of what the actual coolant temp is. It's been that way for so long though, I know exactly how to read it. I'm not sure of any other way to get the gauge working perfectly, aside from using the much larger third gen sensor, or by getting aftermarket gauges. Until I had my gauges all working I ended up using an OBD bluetooth app on my phone. That told me exact engine temp directly from the PCM. Thats how I knew what the gauge cluster was reading in relation to the actual engine temperature.

 

Oh, I I see. I thought you were talking about 98 vs LS3. Who cares if your gauge reads different now because all you want to know is normal versus not normal. If you're driving around worried about the exact temp then you need to upgrade your cooling system. Shouldn't even have to give it a second thought if it is working right.

 

The three wire coolant temp sending unit is GM # 12551708

 

I used the 98 sensor and the gauge reads correctly to what is being reported by the sensor to the ECM, in my 92 Firebird

 

I purchased the 3-wire GM Coolant temp sensor p/n 12551708 and the associated pig tail. With this sensor I am unable to get the temp signal to the PCM and gauge.

The one pin which is by itself is associated with the blue wire on the pigtail. This is the wire I would assume provided the signal to the gauge. I am only getting a signal from the grey wire. Black is ground.

The grey wire will provide signal to the temp gauge and if I connect it to the signal wire for the PCM, the PCM will show the correct temp. Regardless of how I integrate the blue wire to the PCM or gauge, neither responds. Confirmed continuity with the blue wire as well.

How have people wired this sensor?

 

The housing is the ground for the 3rd pin.