Temperature gauge stuck wide open.

[72timemachine]

Hello,

As the title suggests the temp gauge is reading all the way past 260 degrees. Now, I am familiar that there is a difference between the coolant sensor (two wire connector located near the thermostat housing) and the temperature sensor ( single green wire located between cylinders 1 and 3 on the driver's side cylinder head).

I did clean both the green wire's metal connector and the temperature sensor's single connection prong with a wire brush and some fine sandpaper to insure a good clean connection, however, the temp gauge is still reading 260 degrees if the key is turned in the on or off position. It does not matter if the engine is hot or stone cold, it's always at 260 degrees.

Is there a way to test the temp gauge if I dig it out of the dash cluster or has someone experienced this same problem and had to replace the gauge. Is there also a way to test the temperature sensor if I remove it from the cylinder head, I have a multimeter. I tried to search for old posts on this topic but did not find too much on this topic so if anyone has a good post covering this exact problem, that would be great.

Thanks for any help, much appreciated.

[Just call me Sean]

Unplugged the gauge will show cold, grounding the sensor wire will peg the gauge hot. If the gauge shows hot with the sensor unplugged then I would suspect the wire is grounded somewhere. If the gauge is showing hot and you are going to the trouble of taking out the cluster I would remove the sensor wire from the connector and see if the gauge shows cold. If it still shows hot I would suspect the gauge or a problem with the cluster.

[ChevyTech]

As stated, If you unplug the wire from the sensor the gauge should read cold with the key on.

If you ground the wire that is suppose to plug on the sensor the gauge should read hot with the key on.

You can use the specification for the coolant sensor by the thermostat to test the sensor for the dash gauge.

Coolant sensor approximate resistance specifications:
177 ohms @ 212 deg. F. or 100 deg. C.
241 ohms @ 194 deg. F. or 90 deg. C.
332 ohms @ 176 deg. F. or 80 deg. C.
467 ohms @ 158 deg. F. or 70 deg. C.
667 ohms @ 140 deg. F. or 60 deg. C.
973 ohms @ 122 deg. F. or 50 deg. C.
1188 ohms @ 113 deg. F. or 45 deg. C.
1459 ohms @ 104 deg. F. or 40 deg. C.
1802 ohms @ 95 deg. F. or 35 deg. C.
2238 ohms @ 86 deg. F. or 30 deg. C.
2796 ohms @ 77 deg. F. or 25 deg. C.
3520 ohms @ 68 deg. F. or 20 deg. C.
4450 ohms @ 59 deg. F. or 15 deg. C.
5670 ohms @ 50 deg. F. or 10 deg. C.
7280 ohms @ 41 deg. F. or 5 deg. C.
9420 ohms @ 32 deg. F. or 0 deg. C.
12300 ohms @ 23 deg. F. or -5 deg. C.
16180 ohms @ 14 deg. F. or -10 deg. C.
21450 ohms @ 5 deg. F. or -15 deg. C.
28680 ohms @ -4 deg. F. or -20 deg. C.
52700 ohms @ -22 deg. F. or -30 deg. C.
100700 ohms @ -40 deg. F. or - 40 deg. C.

[72timemachine]

Thanks to the both of you, allow me some time to make some tests and I will post what the problem was...thanks.

[d4hartley]

Originally Posted by 72timemachine

Thanks to the both of you, allow me some time to make some tests and I will post what the problem was...thanks.

Did you ever figure this out? Bad gauge?

[72timemachine]

While I am uncertain of how many ohms a properly operating temperature gauge should read, I did notice that the one I bought out of a salvage yard did show a different ohm reading than the current temperature gauge which was stuck way past 260 degrees. The readings were 52 ohms on the "working" gauge I bought at the salvage yard and 48 ohms on the faulty gauge reading way past 260 degrees. This, come to find out, was only half of the problem.

Turns out, the dash cluster's circuit board was also faulty. I proved this out by installing a good used one in place of the faulty circuit board. The gauge reading above 260 kept doing the same thing whereas the other gauge from the salvage yard worked correctly reading zero degrees with a stone cold engine. I did also placed these two gauges in the faulty circuit board and had the same results with both gauges...they both went straight past 260 degrees when the key was turn forward to energize the gauges. So I concluded that I had a bad gauge and a faulty circuit board. The temperature gauge has been working correctly for several weeks now...hope this helps but I sure would like to know what the correct ohms are for a properly functioning temperature gauge. Thanks again for all the help.