Today I found out that my temp gauge is off by about 25 degrees. My question is what would cause it to be that far off? And What are my options/ what should I do as far as fixing it?

 

What are you comparing it to? IR thermometer? ECM readout?

The gauge sensor might be going bad, the ECM temp sensor might be going bad, the heat distribution in the engine is a big factor, etc, etc, etc.

You can measure the sensors and compare them to the CTS resistance values (do a search).

Hope this helps.
Lou

 

Im comparing what was show on the temp gauge in the car to what the scan tool was showing, ECM readout.

I went out and bought some resistors: a 47ohm, 100ohm, and a 220ohm. These were the closet ones I could get. I have a question its probably a dumb question but oh well. How do I put the resistor on the wire? Do I just put on end of the resistor in the wire connector and the other end to a ground? Or do I have to cut and solder the resistor into the wire?

 

As I said, the gauge sensor might be bad or even the ECM sensor might not be good anymore. You would need an infrared thermometer to get a readout on the engine itself to see which sensor is not right.

What are you trying to do with the resistors? If you're trying to see if the gauge shows right then you can just disconnect the plug from the sensor and put the resistor leads in the holes. If it's just a single wire plug, then put one resistor lead in the connector and connect the other one to the ground. Then with the ignition, read the ECM reported temp or look at the temp gauge (whichever you put the resistor on) and see if it's showing right.

But if you have an ohm-meter, you can measure the actual sensors and see if they report the right temperature.

Lou

 

If the ECM sensor was bad, and my gauge was somewhat accurate, than that would mean my car was at 255-260 when we had the scan tool hooked up, but the coolant wasn't boiling or anything into the overflow tank. And the fan turned on exactly when he told me it would when we were watching the scan tool, at 227. And it turned off exactly at 213 according to the scan tool. So I'm thinking its my gauge or the temp. switch.

I was trying to see if my temp gauge would show the correct temp when I added the resistor. I disconnected it from the switch and the gauge read nothing, then grounded it and it pegged out, went way past 260. I added first the 47ohm resister into the end of the connector then grounded it with the other side, and the gauge didn't move at all. Same thing with the other resistors 100ohms, and 220ohms. I'm going by the gauge in the dash. Am I not getting a good enough connection, or is my gauge broke/incorrect?

Tomorrow when i get back from the shop I'll measure the temp switch sensor with the ohm meter, and I'm guessing that I just put the positive lead onto the sensor and put the black lead to a ground?

 

Make sure you have 47ohm, 100ohm and 220ohm resistors. If they are by a chance in kilo-ohms, that would make the gauge show nothing (all the way down - cold).

Since the gauge shot up to way past hot when you grounded the wire, that's good - it shows that you have a connection from the sensor plug to the gauge.

Now it's just a matter of figuring out if it's the gauge or the sender.

Lou

P.S.: Yes, one lead on the temp sender, one lead on the block. Set the meter to 10kilo-ohms (or whatever nearest higher value - 20Kohm or so).

 

The resistors I have say this: 47-Ohm Resistors 1/2 watt 5% tolerance. Than the 100ohm and 220 ohm resistors say 1/4 watt 5 % tolerance. Im guessing these are these the wrong ones?

 

If it says "ohm" then these are the right resistors. "Kiloohm" would be wrong.

If these resistors don't make the gauge show the right temperature (47ohm shold make it shoot to 250F, 100ohm should show 230F and the 220ohm should show 200F), it's safe to say that the gauge is not good.

Just make sure that you're connecting the resistors right (one lead into the connector and one lead on the block) and with the key in the ON position. If that doesn't show anything on the gauge, it's most likely bad now.

BUT, didn't you say that your gauge worked but it was just inaccurate? In that case the resistors SHOULD show something on the gauge.

Lou

 

Yeah they say ohm. I'll try again when I get the car back today. I bought more resistors; 50 Ohm 10 watt Resistors, 100 Ohm 10 watt resistors, and 100 Ohm 1 watt resistors. But the number of watts shouldn't matter?

 

Absolutely correct, the number of watts doesn't matter for this purpose. Just make sure that you put one lead from the resistor in the temp gauge connector and the other lead from the resistor on a GOOD ground, like the block. If you don't find good ground, the gauge will show nothing.

Hope this helps.
Lou

 

Got the car back just now, and tested the temp switch with an ohm meter. It read 165 ohms, which would probably mean about 215 degrees Fahrenheit. I put the connector back on the temp switch and the gauge showed 230. I'm going to retest the resistors, when it cools down cause I don't think I grounded them correctly the first time.

 

I retested with the resistors and heres what I came up with. With the 50 ohm 10 watt resistor, the gauge went way past 260. Then I used the 100 ohm 10 watt resistor and it showed about 222-225 on the gauge. Then I used the 100 ohm 1 watt resistor and it showed the same thing 222-225. So what does this mean? With 50 ohms it went way past what it was suppose to show, 250. But with 100 ohms it showed below what it was suppose to. Can I safely assume that my gauge is bad?

 

Yes, the gauge seems a little off in that case.
If you need another gauge, PM Stephen (https://www.thirdgen.org/forums/memb...-stephen.html), he's got a whole set available.

Lou

 

So would I need a whole new cluster, or what? Should I even mess with the stock gauge, or just buy an aftermarket one and mount it in a gauge pod?

 

You can replace just the gauge, no need to change the whole cluster.
The decision whether to go aftermarket or stay with the stock gauges is yours.

Lou