'60 temp gauge/sensor

[Matt F.]

Hello -

My just-recently running '60 has a non-working temperature gauge. Having read posts on this board and elsewhere, I have installed a Standard TS6 sensor (which provides approx. 610 ohms when cold), and my gauge has power, but the needle never moves from the zero position. I think I understand that impedance decreases as the temp. of the sensor increases, so I would assume that as impedance nears zero, the needle should move all the way to the right? Anyway, can anyone advise me on a simple method (for someone with very little electrical understanding) to verify that the gauge is not to blame?

Thanks
-Matt

[Ed Jennings]

Re: '60 temp gauge/sensor

1. Disconnect the sensor wire from the sensor. 2. With the ignition on, touch the wire to a good ground. The needle should deflect to full scale (hot). If not, you probably have a bad gauge. However, before you condemn the gauge, hook a test wire to directly to the sende terminal of the gauge and repeat step 2. If it works at this point, you have an open circuit within the wiring. If not, you likely have a bad gauge. The sender should read about 700 ohms resistance at ambient temperature, 70 degrees or so. If the needle on the gauge won't move, the sender isn't the immediate problem. You need to first determine if the gauge and wiring are ok. The 610 ohms you report is a little low, and a properly working gauge will indicate a few degrees too high with this sender.

[Jack H.]

Whoa!!!!

The resistance/temperature curve specified for temp sender is a non-linear relationship that was changed by engineers a plurality of times over time. Specifically, the transducer's transducer's transfer function is non-homoscadicious (mean and standard deviation change with time).

That's why all the catalogs that advertize 'real McCoy' AC senders take a disclaimer on accuracy (typical statement of +/- 30F). It's also the reason the temp gauge(s)in the dash are INTENTIONALLY fuzzy in terms of gradicles and mid-range calibration (maybe one legend at 180F or 200F near mid-scale and no labeling elsewhere). Point is, the system just wasn't very accurate across its dynamic range.... The thing that mattered was NOT typical/normal engine temp but entry into abnormal OVERHEAT range.

Folks that buy these cars keep trying to make something that WASN'T out of the temp gauge--accurate across its entire dynamic range. The alternative back then was an 'idiot light' that basically said you just kissed your engine goodbye. We forget what the technology WAS in the 50's and 60's and want it to mirror today's cars....

At 'room temp' (69F), the AC sender's resistance is NOT even specified by GM! Therefore, allusion to what is/isn't a typical transducer room temp reading is foolish....

The tolerance band for acceptable resistance deviation across the sender's T-R response is also non-linear. Wider than a loose goose at the low end of the response curve spec (about 130F) and tighter than a drum where it counts--engine about to enter overheat/danger range.

Basically, from the low end of the response curve spec the allowable resistance range for an acceptable sender varies in the 500-1200 ohm range (a HUGE delta)! At the upper end of the response curve spectrum, the resistance response tightens to roughly 8 ohms. The upper end temp asymptote of the sender's response cuver is 40 ohms.

If you cram the sender wire to B+ ground, I guarantee you, you'll peg the (*&&& gauge in the instrument cluster to/beyond it's mechanical rails! Advising such is a real good way to grenade the movement and if left there for any appreciable time you just might kiss the temp gauge goodbye!

Now, if you meant have an observer sit in the cockpit while a helper MOMENTARILY grounds the temp sender wire, OK I'm with you. But, say that! Don't say ground the meter without knowing what the listener knows or doesn't know about the system.....

If you MUST devise a method to peg the temp sender, than do it within GM system specs and current limit the sucka as designers intended by connecting a 40 ohm resistor in series to ground at the end of the temp sender's harness lead.

[Ed Jennings]

Re: Whoa!!!!

Jack, you are correct, as usual. I should have specified that the sender wire be momentarily grounded. The conventional wisdom seems to be that a C1 sender that reads about 700 ohms @ ambient temp will usually provide REASONABLE accuracy with most gauges. Those that have a different value usually don't. Unless one can put the sender in a pot of water and read the resistance over a wide range of temperatures, it's still a crap shoot.

[Jack H.]

Right on!

Room temp readings will 'correlate' to in-band resistance readings, but that's about all you can say, UNLESS you want to put your ohm meter across the sender and immerse it in a pot of boiling water AND do a table look up to the GM spec (which version over time?????).

The BIGGEST realization here is NOT to permanently ground the temp wire (electricity moves at the speed of light and you can't get around and climb inside to look at the guage that fast) to do a go/no-go test of the temp gauge!!! If you're wrong in your hypothesis (the gauge is bad), this method of
verification is pretty sure to generate a POSITIVE hypothesis test....
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Last, point I was making 'between the lines' is the temp gauge system in early Corvette was:

(1) A cut above idiot light technology.
(2) NOT intended to be accurate across the dynamic range of the gauge.
(3) Mid-range readings could vary with the 'phase of the moon' ESPECIALLY in straight axle Corvette where B+ varied with generator output (almost nill at idle).
(4) INTENDED to be accurate 'where it counts' (OVERHEAT threat).

And SO MANY enthusiasts in our club sit, look at the gauge in the cockpit during NORMAL engine operation, see it looks a tad high, fear they have the Sword of Damacles hanging over their heads, and spend INORDINATE time/$ trying
to FORCE the mid-range reading to be accurate!!!!

Heck, there was even an article published in Restorer a while back that advised folks to splice a series resister in-line with the temp sender to 'trim' the temp gauge for mid-range accuracy!!!! If you understand what I said about the inherent non-linear nature of the sender, you'll see why this is a BAD idea....

By FORCING mid-range accuracy on the gauge, you inherently skew the gauge's high end asymptote! You 'could' push the system over its 'rails' with such a move. Meaning: the guage would read hot but not dangerously hot when, in fact, your engine has/is in thermal melt down range!!!!!
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So, if one HAS to insist on the temp guage being accurate from mid-range to overheat, then go make it accurate. Guys like Fred Oliva at Vintage Automotive Reseach have the tooling to get a T-zero reading on your car's specific temp gauge, and hand select a temp sender to match your gauge....
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But, in this case, the poster was essentially trying to establish a 'go/no-go' test for his gauge. So, I've stepped beyond the intital query...

Good night, everyone!!!

[Roberto L.]

Re: Right on!

Hi! understand your point (good posts). After several years driving my 70, which I suspect/can't be sure, has original temp sender y gauge, common reading seems to be too low but correct. Usually between 1 quart and less than half reading. Sometimes, under certain conditions (winter) I may watch the thermostat opening, needle approaches (but not reachs) half reading and then descends again. At those readings the car drives quite well.

Some years ago, when I broke my fan clutch, I was in highway and temp start to climb slowly but steady, at three quarts I had to stop the car fast! and signs of boiling was there. Obviously at shut down the car had their pants wet! No further damage of engine or anything just a brief overheat situation,. What I mean is that the gauge reading is not very accurate but apparently was design to show more relative readings than showing exact temp readings like a calibrated thermometer. And it worked at the critical situation where it should be.

Roberto, NCRS #30019, RMC

[Ed Jennings]

What you really have to do is

Know what is the NORMAL reading for YOUR CAR. You can, and should, verify the gauge reading with an infrared (best) or stem type thermometer. Then when the gauge indication exceeds what is NORMAL, whatever normal may be, you know your temperature is climbing and you need to do something.

[Matt F.]

Re: What you really have to do is

Wow, great responses. Since I just woke up, I haven't destroyed anything yet, and I was planning to climb under the dash with a temporary wire and momentarily ground the gauge, which I guess is still a reasonable course of action. Thanks all for presenting some realistic expectations of gauge accuracy/function.

If the gauge does turn out to be bad (please NO!), what are my options? This does not appear to be a readily replaceable part, so I would hope a repair could be made. Now I'm understanding why there was a capillary-type aftermarket gauge dangling under the dash when I bought the car!

Matt

[Ed Jennings]

Re: What you really have to do is

If you don't have a helper, you can ground the wire so it will stay put, with the ignition off, and then momentarily turn the ignition on while you watch the gauge.

[Jack H.]

Driveline....

reading it, you'll find lots of instrument repair services offered. Bear in mind, Chevy had several means of gauge calibration. One way was to hook the gauge to a calibrated electrical 'nest' (designed to simulate overheat) and install the gauge pointer oriented to the danger zone. The other way (later gauges starting around '65), was to connect the gauge to another 'nest' (also aimed at simulating overheat), then worker picked from a bin of precision, wire wound triming resistors and installed the appropriate resistor onto the back of the gauge. Often, someone before you has been 'in there' and the gauge's original triming resistor is bye bye resulting in inaccuracy.

So, as many of the instrument facilities do concours gauge face restoration, I'd be asking 'em HOW they re-cal the gauge in the course of their business. If you get a 'dah' response, keep on shopping....