Easy Coolant Temp Sensor Fix

[scss02]

I have a 1985 SWB. For my swap I used a 2004 5.3. For my gauges i used a 91 suburban cluster. I wanted everything to look stock and did not want to use a aftermarket temp gauge. So instead of drilling the head or buying an adapter, I found an easy solution. I am using a 2004 temp sensor with the 91 gauge

1 Go to Radio Shack or local electronic store and find a variable resistor or a Potentiometer.

2 If using a Potentiometer hook up the signal wire between the sensor and the gauge to the middle connector and one of the outer connector.

3 Start the engine and warm up to operating temp. (Having HP Tuner is the best way to verify this)

4 When truck is at operating temp. Turn the dial (or adjust variable resistor) till the gauge reads the desired temp.

5 Loc down the Potentiometer or variable resistor. (I soldered mine)

Hope this helps

[Mr. 250r]

A few of us are also running 91 gauges but what we did was just have your original temp sensor milled down to fit the passenger head i can't remember the size its in my suburban build thread i believe i figure that's the easiest solution

[Dustytrix]

Good info scss02 I will try to remember that on the next swap. I have a potentiometer that I used to figure out key resistance on a 90 camaro, then went and bought the .50 cent resistor and soldered it in.

[Jonce]

Originally Posted by Mr. 250r

A few of us are also running 91 gauges but what we did was just have your original temp sensor milled down to fit the passenger head i can't remember the size its in my suburban build thread i believe i figure that's the easiest solution

^^^ I did this on my '93 S-10 with 5.3L and it worked great for the 2yrs I owned it (17k miles) with zero issues. I thought that was the easiest solution as well.

[littlevictories]

I tried turning a '66 sensor down on the lathe. No bueno, not enough material before you hit the guts of the sensor.

[scss02]

Originally Posted by Mr. 250r

A few of us are also running 91 gauges but what we did was just have your original temp sensor milled down to fit the passenger head i can't remember the size its in my suburban build thread i believe i figure that's the easiest solution

I tried this as well. The sensor I tried it on did not have enough meat on it. By doing it with a potentiometer, I did not have to mill anything down. It took about 10 minutes to wire and adjust. And a potentiometer only cost $1.99.

This is the third truck I have wired. The first two we drilled and tapped the head. I did not want to do that on this one.

[littlevictories]

I'm gonna give this a try. It might just be really early, and not enough coffee but I'm not quite picturing this. Do the 90's gauges run off two wires?

Originally Posted by scss02

2 If using a Potentiometer hook up the signal wire between the sensor and the gauge to the middle connector and one of the outer connector.

[ls1nova71]

90's gauges use one wire, I believe he's talking about the two wires coming off the potentiometer, one to sender, and the other to the gauge. My concern though is that the gauge won't be linear in it's movement. I tried the same thing a long time ago by calculating the resistances and then put the correct resistor in line, and although I did get the gauge to read straight up at 195*, but when it got a lot hotter, the gauge didn't show it, if that makes sense. It moved a little more to the right, but not into the red part of the gauge, and clearly should have been.

[dayj1]

Originally Posted by ls1nova71

90's gauges use one wire, I believe he's talking about the two wires coming off the potentiometer, one to sender, and the other to the gauge. My concern though is that the gauge won't be linear in it's movement. I tried the same thing a long time ago by calculating the resistances and then put the correct resistor in line, and although I did get the gauge to read straight up at 195*, but when it got a lot hotter, the gauge didn't show it, if that makes sense. It moved a little more to the right, but not into the red part of the gauge, and clearly should have been.

The response curve of a temperature sender is not linear. When cold, the resistance is very high, often in the kilo-ohm or even mega-ohm range. As it heats up the resistance drops, but at an exponential rate. In other words, the added resistance from an inline resistor (or pot) is irrelevant at low temp, but skews the gauge more and more as temp goes up. The best you'll ever get with such an approach is a gauge that is accurate at a single temp.

Also, if I understand the OP correctly, the '91 gauge is spliced into the 2004 temp sender. If a separate '04 sender was used in the passenger head, then no harm, no foul (except a bad gauge reading). If the gauge was spliced into the driver's side sender along with the PCM, then all bets are off on what the PCM thinks the engine coolant temp is due to the load placed on the circuit. A bad temp reading could definitely effect how the PCM controls timing, etc.

[littlevictories]

Originally Posted by ls1nova71

90's gauges use one wire, I believe he's talking about the two wires coming off the potentiometer, one to sender, and the other to the gauge. My concern though is that the gauge won't be linear in it's movement. I tried the same thing a long time ago by calculating the resistances and then put the correct resistor in line, and although I did get the gauge to read straight up at 195*, but when it got a lot hotter, the gauge didn't show it, if that makes sense. It moved a little more to the right, but not into the red part of the gauge, and clearly should have been.

yeah thats how my fuel gauge works with the resistor fix works. reads nice at half tank, but above and below it's wildly inaccurate. more of a GO GET GAS DUMMY indicator than anything else

[scss02]

The response is not linear (and yes it a separate sensor in passenger side head). When I was testing, the temps above 195 were not dead on correct, but it did show enough of a response to show if I was starting to overheat. Example if my gauge goes above 210 and beyond I know I have a problem. At that point I hook up my lap top and double check what the computer is reading. My truck is not set up for racing or anything else. If that was the case I would be using Auto Meter Gauges. This is just an easy way to keep stock gauge (which are not that accurate to begin with).

[littlevictories]

word. i hope you didn't think i was knockin ya.
it's a pretty elegant solution
100% agree on the stock gauge's accuracy and autometer sentiments.

[scss02]

Originally Posted by littlevictories

word. i hope you didn't think i was knockin ya.
it's a pretty elegant solution
100% agree on the stock gauge's accuracy and autometer sentiments.

No worries. I just wanted to be clear on my intentions with this, I was trying different options. To see what worked for what I wanted to do. Not everyone has access to a machine shop (can afford) or skill to drill and tap or turn down a sensor, luckily I do. I have experimented with a few things on this truck, some things worked some did not, but that is the fun part for me.

[kvn1011]

good info