3 wire vs other temp senders

[87Skier]

How does the 3 wire temperature sender from a 1998 F-body compare to the older style temperature senders like the Gen I vortec stuff and the older Gen I engines? Does the gauge read accurately?

Does the ecm still receive the proper reading when going from a later 2 wire to the 3 wire sender?

[72MARIO]

It does not read correctly in my 1968 suburban. It reads very cold. There is a thread with part numbers for one from a jeep wagoner that works properly.

[mongocanfly]

I run my temp gauge sender off the passenger head at the rear..the ecm uses the sender on drivers side head..

[87Skier]

I did some searching and didn't see a temp sender I liked and didn't want to deal with machining a temp sender to fit or drilling out and tapping the other head to accept the older style temp senders, so I bought the 3 wire to do some testing.

If you are using the stock 67-72 gauge you know it doesn't have temperature marks, so I just did a best guess and decided to fit the lines to about where I wanted the normal running temperature to be. The picture below shows how I defined the temperatures. I determined the resistance at these points and plotted them.

The temp sender was heated in oil. Temperature was monitored with a candy thermometer. Resistance was checked with a multimeter.

The line denoted resistor network is adding in additional resistors to bring the gauge into calibration.

From the graph you can see that there is very little difference between the lines from 155 to 205, so this will be fairly accurate. The resistor I'm going to use is a 147 ohms (100 + 47), which produces the green line. See the diagram for connection.

The green line can be shifted up or down by changing the resistor. A 100 ohm resistor moves the line down, meaning that at 200 degrees, the gauge will see less resistance making it read hotter than if a larger resistor is used.

[mongocanfly]

Somebodys been doing their homework..

[Ecc10]

Great info,
what is the part number for the sender u used?
where did u buy it?

[87Skier]

Sorry for the delay for anyone looking at this thread.

I used this sensor: ACDELCO 12551708

Since I've been driving the truck, 200 degrees on the computer is directly at the top of the gauge. If anyone is doing this, I would recommend finding a resistor with slightly higher resistance (from 147 to about 160 ohms). This is purely a stylistic choice as many automakers tend to always have the gauge reading slightly below mid-range.

[gringoloco]

Great info here, thanks!

[Steve Cole]

Forgive my stupidity, can you clarify the 2 wire or 3 wire part? Also, what wattage resistor did you use?

[87Skier]

The early F-body cars with LS engines used a 3 wire temperature sender. Two of the wires go the ECM, and the other is a standard temperature gauge. This was later changed when the instrument clusters started using the reported signal from the ECM.

ACDELCO 12551708, is for a 1998 Camaro with the 5.7L. The picture clearly shows 3 pins in the sender. Most only have two.

I used a 147 ohm resistor, but would recommend something closer to 155 ohms.