I am getting a temp reading on my 65 that is 20 or more degrees higher than my IR gun. Has anyone heard of or used a resistor in the line to correct this? A local shop told me that this may be a way to correct this. Or is a gauge and sender in my future?

Thanks,
Fred Z.

 

A ton of posts on this. The temp sending units typically read notoriously high. Most here have gone to the Wells TU-5; sometimes buying several of them and going with the most accurate one. You can put a resistor in the circuit but the results won't be linear...it will only be accurate at the temp where you selected the resistor and accuracy will vary at any other temp. This works (kinda) but you have to be aware of the variances.

Interestingly, this is the fix that SeaRay came up with on my boat to adjust the gauge readings....cheap way out I guess.

I have some charts of what the ohms should read on various sending units at certain temps if you want to look at that.

 

I put a parabolic gauge under the dash and use it in conjunction with the factory gauge. Factory gauge always reads hotter. Doesn't overheat so I don't really care.

 

I had this problem with my 1966 L79. I thought I may have a bad guage or a bad ground. I got the temp gun from AutoZone and confirmed the engine temp right at 180*. I then bought temp senders from ZIP, AutoZone, Advance Auto and Napa. They all gave different readings, anywhere from 160*-210*. The one I selected (NAPA) reads about 170* and that is the one I have in it now. All are less than $10 except ZIP (around $25).

Mark

 

I found the Wells Tu5 to match the IR gun:

 

I spent a ton of time on this. The IR gun method, IMHO, is not completely accurate. With the IR gun, you are reading the surface of the intake (or wherever you are taking the reading), which is cooler than the water temperature that the sensor reads. What I did was:

1. Bought new sensor and a 0-1000 Ohm variable resistor.
2. On the stove, I gradually heated a pot of water on the stove with the bottom of the sensor submerged and a multimeter measuring the resistance output while measuring the water temp with a known good thermometer. I made a table/graph of resistance vs temperature for the sensor. You can verify your calibration thermometer if you use distilled water and boil it - should read 212F.
3. I hooked up my variable resistor to the sensor wire and ground at the intake manifold where the sensor goes. I made a table/graph of variable resistance reading vs temp gauge reading. Note that the gauge is very sensitive across its range and the curve is a bit flat, so you have to be precise.
4. I then chose the additional resistance needed to make the reading correct. It is true that the reading is not perfect across the entire range. I chose a resistor that was spot-on at about 190 degrees ( I think I have 22 Ohms). Over the range of interest (160-230), it is very close.
5. Solder the resistor to appropriate plugs on each end and shrink wrap and insert. If you don't mind being able to see it, put it under the hood. If you want it hidden, put it behind the gauge.

Of note, one of my earlier attempts was to buy a "calibrated" sensor from one of the popular venders which included a resistor jumper like the one I made. However, it did not read correctly on my gauge. Could be my gauge is off, but if you are calibrating the sensor yourself, who cares?

Like I said, this was my method and it worked for me.

Cheers
Greg

 

I doubt that either of these approaches are "completely accurate". The toss up is between taking the temp of the metal surrounding the hot water with an I/R gun vs calibrating gauge resistance at a single point in the temperature spectrum. Pick your poison.

 

Hello Fred. I've been using a resistor for my temp gauge on my 57 for several years now. Up until last weekend, it has seemingly stayed fairly accurate since I dialed it in with my IR gun. Last Sunday my wife and I were returning from a cruise when the gauge kept climbing. We were going up a hill, so I didn't think much about it until it pegged to the right. I popped the hood, no sign of severe overheating, so I left hood popped to allow hot air out and carefully drove home, since I was close by. When I got home, I grabbed my IR gun - temp was about 200*. I re-adjusted the resistor to match the IR reading, and so far so good. Apparently something caused this to happen, just don't have a clue what. Needless to say, I don't trust the gauge anymore.

John

 

It amazes me that getting a temp gauge to read accurately is such a headache. My '67 Chevelle had cheapo SunPro gauges in it and the temp read high by 20*-25* and scared me driving in Orlando summer heat. I put in a set of AutoMeter gauges and the temp is within 5* of what my I/R gun indicates. MUCH less stressful when cruising now.

 

Has anyone tried the recalibrated temp senders from Dewitts or Ecklers? They are advertised as being accurate.

http://www.dewitts.com/collections/a...e-sending-unit

http://www.ecklerscorvette.com/corve...1957-1967.html