Cylinder Head Temp Gauge - 66 Corsa

[rnd5553]

My newly installed Corsa dash in my 66 Monza cly. head temp gauge is not working. The thermister checked out using OHM meter prior to install. Below is a response on this same subject from years back on a EM car.

Are the readings (specs) the same for a LM car. It looks like I need to check the resistance from the wire coming off the thermister what should I be looking for reading wise. Thanks.

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"there are two electrical connections on the cylinder head temperature gauge. One is a simple 12 VDC power connection to power the gauge. The other is the wire connection between the gauge and the thermistor in the cylinder head. Assuming that the gauge is functional and has power (indicated by the initial needle deflection you described when you turn on the key), the first thing you need to do is check for electrical continuity between the gauge and the thermistor. This can be done by disconnecting the thermistor wire from the gauge at the instrument panel, and using a multimeter (set to measure resistance in ohms). You should be able to ground one test lead of the multimeter to a chassis ground, and touch the other test lead to the thermister wire with a resistance reading that reflects the cold reading that would be expected according to the above referenced graph (> 1000 ohms). (If you run the engine, this resistance reading should change as the engine heats up). If you measure an "Open" condition with your multimeter (no continuity) you will need to trace the wire and check for a damaged lead or corroded/loose connection at any connector between the instrument panel and the thermistor." per previous post.

[cnicol]

At room temperature, the thermister will return about 3000 ohms (with a wide margin for variance)

[bbodie52]

Check to ensure that the power connection is providing proper voltage to the gauge when the key is ON, and that the housing of the gauge is properly grounded. Also check for electrical continuity between the thermistor and the gauge in the instrument panel.

You can view detailed Corsa wiring schematics (end-to-end) using the following link...

Corvair Combined Wiring Schematics
viewtopic.php?f=225&t=12968

[rnd5553]

ok, so with my ohm meter set @ 2000 on the scale, I'm getting readings of 101 ~ 98 on a cold engine when checking at wire coming off the thermister. So is this ok or???

[bbodie52]

I'm not really sure with the resistance rating would be through the thermistor. What I would recommend is temporarily disconnecting the wire from the thermistor and attaching it to chassis ground. Then recheck the resistance between the wire at the gauge location and ground. The sensor wire should have a resistance of approximately 0 ohms, which proves continuity and that the wire is in good condition. Once you have proven the condition of the wire it can be reconnected to the gauge and to the thermistor. You should also confirm that you have a good ground connection between the gauge housing and chassis ground, and that you have 12 V DC powering the gauge when the key is turned on.

If you have a good ground, good source voltage, and good connectivity to the thermistor from the gauge, the only thing left to question is the gauge itself and the sending unit.

[63Spyderd]

The following simple test can help you troubleshoot your gauge/sensor; no ohmmeter is necessary

1.) Remove the wire at the thermistor and turn the key to the ON position.

Your gauge should report less than 200 degrees.

2.) Now ground the wire at the thermistor.

Your gauge should report greater than 600 degrees.

[CorsaCharlie]

Here are some diagrams I made when working on a '65 Corsa :
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Head Temp Gage Circuit

Head Temp Thermistor.jpg (11.9 KiB) Viewed 1845 times

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Testing Head Temp Gage

Head Temp Gage~Testing Thermistor.jpg (14.42 KiB) Viewed 1845 times

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Corsa Dash Temp Gauge Thermistor Temp~Ohm Scale

[cnicol]

ok, so with my ohm meter set @ 2000 on the scale, I'm getting readings of 101 ~ 98 on a cold engine when checking at wire coming off the thermister. So is this ok or???

You have to disconnect the thermister wire and you have to set the ohm meter to a higher scale. Room temp thermister resistance should be around 3000 ohms, give or take 1000.

[63Spyderd]

ok, so with my ohm meter set @ 2000 on the scale, I'm getting readings of 101 ~ 98 on a cold engine when checking at wire coming off the thermister. So is this ok or???

"checking at wire"?

Are you measuring the resistance of the thermistor or the resistance of the wire through the gauge? Since you have previously verified the thermistor was good prior to install, neither measurement is likely to get you closer to a diagnosis.

[gcjacobs]

Hi there, So I am having a similar issue with my head temp gauge on my 65 corsa. I took all the advise here and applied it :) The thermister seems to be working fine registers between 1920 and 1550 (there abouts) cold...warmed it up a bit and it goes down to about 620 (just letting it idle in the driveway for about 5 to 10 min or so). So it seems to be working...

However when I measure continuity to the gauge, I am getting about 58.8 ohms, not the zero I should, as stated above. I measured it with the key off, wire disconnected to the thermister, and testing from the wire at the connector in the engine compartment (side going to the gauge) to the battery (neg ground). Maybe I am getting something through the harness? Maybe I didnt understand the directions (very possible)...any help is appreciated.

[63Spyderd]

The following simple test can help you troubleshoot your gauge/sensor; no ohmmeter is necessary

1.) Remove the wire at the thermistor and turn the key to the ON position.

Your gauge should report less than 200 degrees.

2.) Now ground the wire at the thermistor.

Your gauge should report greater than 600 degrees.

[66vairguy]

Hi there, So I am having a similar issue with my head temp gauge on my 65 corsa. I took all the advise here and applied it :) The thermister seems to be working fine registers between 1920 and 1550 (there abouts) cold...warmed it up a bit and it goes down to about 620 (just letting it idle in the driveway for about 5 to 10 min or so). So it seems to be working...

However when I measure continuity to the gauge, I am getting about 58.8 ohms, not the zero I should, as stated above. I measured it with the key off, wire disconnected to the thermister, and testing from the wire at the connector in the engine compartment (side going to the gauge) to the battery (neg ground). Maybe I am getting something through the harness? Maybe I didnt understand the directions (very possible)...any help is appreciated.

You are NOT checking continuity of the wire, BUT the continuity through the wire AND gauge to ground. Your number is about right. To check only the wire you would have to unplug it from the gauge and connect the meter to both ends of the wire - a challenge due to the location.

Unmolseted - the LM gauges were reliable. Typically connector corrosion, bad grounds, or bad wiring causes problems. Keep in mind this system was never that accurate and the thermistors do drift with age. The engineers had to make a non-linear gauge response AND deal with variations in system voltage. Considering everything the system worked well for the technology available, just not that accurate.

What most folks do is observe where the needle is during normal driving and if the needle goes above that "normal position" it's time to check the engine for overheating. Of course the needle will indicate a higher temperature during full power and hill climbs, so you have to learn what is acceptable and what indication is above normal.

[gcjacobs]

thanks for the info...so it seems at least that I have continuity through the gauge. So I tried what 63spyderd suggested and ground my gauge from that same wire to the battery, and turned the key to on...the gauge jumped to 300, but didnt go any further, and it doesnt go back to 200 now either when I hook everything back up. Should it have? Any ideas why it didnt go to 600 like it seems it should have? Getting to that gauge as you mentioned is a real PITA, so any other tests I can do to test for possible loose connections would be appreciated. Thanks!

[63Spyderd]

What is the position of the needle for Step 1?

[66vairguy]

thanks for the info...so it seems at least that I have continuity through the gauge. So I tried what 63spyderd suggested and ground my gauge from that same wire to the battery, and turned the key to on...the gauge jumped to 300, but didnt go any further, and it doesnt go back to 200 now either when I hook everything back up. Should it have? Any ideas why it didnt go to 600 like it seems it should have? Getting to that gauge as you mentioned is a real PITA, so any other tests I can do to test for possible loose connections would be appreciated. Thanks!

Do not connect the thermistor wire to the battery. Ground the thermister wire to the engine block/head (engine block should be connected to the battery negative side AND chassis GROUND.

What 63 said was --
1.) Remove the wire at the thermistor and turn the key to the ON position.

Your gauge should report less than 200 degrees.

2.) Now ground the wire at the thermistor.

Your gauge should report greater than 600 degrees.

[gcjacobs]

ok...so I redid my test and it all works as mentioned above. with a little help from my finger tapping the gauge (a tip I received from a friend in the corvair club) the gauge climbed to over 600 when the thermistor was grounded to the chassis. Went back to below 200 (with a little more help) when reconnected. So now I think I will try to get the car warmed up, and do a little tapping on the gauge and see if maybe it is just a little stuck.
Thanks for all the help and tests! I can always find an answer on this forum...