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65 Temperature Gauge and Sender Issues

Great team of guys you were with help on my clutch issue. Thanks. My 65 is a 327/350 with Factory A/C convertible. After the engine rebuild, I noticed my temperature was much hotter according the gauge. Easily getting up to 210. Cooling back down to 180-190 on the road, and climbing back up in the space of a few minutes at a light. I checked it with an IR gun and when it reads 210 on the gauge, the IR gun says 190 at the thermostat outlet. 190 at the top of the radiator. 165 coming out the bottom of the radiator. I figured the sender was bad. Read all the information about how mismatched they all are. And each time I replaced one, it was still off. That included one supposedly calibrated from Lectric Limited and one from Corvette Clocks. Finally, I sprang for an NOS one that cost $100. Installed it, and my reading is still off 20-25 degrees. That says it must be the gauge. Maybe. So now I'm wondering do I try and get a reproduction or NOS gauge? And will they be equally as unreliable? I saw that Corvette Central sells an inline adjustable resistor for calibrating the gauge. But I also read that it can only be adjusted accurately for one specific temp. IE, calibrate for 180. And it will read 180 when it's 180. But it might read lower when it is actually hotter. And higher when it is actually lower because the signals are non linear.Wilcox sells a variable resistor for calibrating the gauge at the gauge. But I would really prefer not to take the cluster apart unless I have to. I'm afraid to let the car run when it gets over 210 on the gauge. Because I don't really know where it's going to stop. If I knew it got to 190 at idle without A/C on, or even 210 with the A/C on, but no higher, I wouldn't worry about it. But I can't confirm until I have an accurate way to know without getting out every couple of minutes to check with the I/R. Any ideas? By the way, mine is a 240 degree gauge with 180 in the center. Thanks, Jeff

Submitted by: Jeff Menkes


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I think you’re worrying too much about the hard numbers on the dash and not enough about the actual temperature. Typically we find out what the actual temperature is and if it is within limits the number being shown on the dash becomes the new normal. Most temperature gauges are nothing more than comparison indicators and should only be used to tell when there is a change away from normal. Because there is seldom a gauge that tells the actual temperature it is change that’s important. That said you are making a mistake in the way you’re checking engine temperature. You are using diagnostic readings to try to find actual temperature. What you’re testing would be done once you know you have a problem and are trying to isolate the cause. It should be tested right beside the temperature sending switch and add ten to twelve degrees to the reading for thermal loss through the metal. Once you do that you may find that it is actually running too hot which needs to be addressed. If that is the case look for coolant flow problems for overheating at cruise speeds and look for airflow problems for low speed overheating. Posted by Administrator on 2/29/2016 4:14:44 PM

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