rittenrotton 4 Report post Posted July 11, 2017 I think I have a real problem here and need a more knowledgeable opinion. I have a 70 coupe with a Ford racing 306 motor. I recently rewired the car with the American Autowire kit and I have New Vintage Usa aftermarket gauges. My problem is, I never felt the temperature gauge on the NVU gauge was reading correctly so I bought a new autometer temperature gauge. My problem now is... the New Vintage gauge is reading my temperature as being about 190 but the autometer gauge that I have that's brand-new is tell me that my motor is running at 210. How can I find out which ones accurate? Quote Share this post Link to post Share on other sites
Brian Conway 283 Report post Posted July 11, 2017 With the car warmed up, the gauge reading 190*, the motor running, put a thermometer in the radiator top tank. Most accurate method I can think of. Brian Quote Share this post Link to post Share on other sites
MN69Grande 203 Report post Posted July 11, 2017 I wouldn't open the radiator cap with the engine at temperature. For one coolant temp in the radiator will be less than at the sensor (maybe not not a huge amount but still). For the other that seems like a messy and dangerous thing to do. Beg, borrow, or steal an Infrared heat gun or by one for $30 (there are also some for as little as $10 that look like remote controls but I don't think they are very durable). https://www.harborfreight.com/Non-Contact-Infrared-Thermometer-With-Laser-Targeting-69465.html any hardware or parts store will have them on the shelf. Point it at the sensor/sending unit. It will read a few degrees colder than what the coolant actually is. This should at least tell you which gauge is more accurate. 210 vs 190. Are you using the same sending unit with both gauges? Are the sending unites and gauges compatible? Also once you have the tool you can see how well your radiator is working by comparing the temps for the inlet and outlet hoses going to your radiator. Quote Share this post Link to post Share on other sites
rittenrotton 4 Report post Posted July 11, 2017 Thank you guys, for safety's sake I think I am going to try the Infrared heat gun method, but thank you Brian for the suggestion! Should I get my reading off the radiator hoses and not the block? Yes, I am using the same sending units and they should both be compatible. Quote Share this post Link to post Share on other sites
MN69Grande 203 Report post Posted July 11, 2017 55 minutes ago, rittenrotton said: Thank you guys, for safety's sake I think I am going to try the Infrared heat gun method, but thank you Brian for the suggestion! Should I get my reading off the radiator hoses and not the block? Yes, I am using the same sending units and they should both be compatible. So to check the gauges at the measure at sending unit. The other suggestion just tells you the health of the radiator. You can gauge how much heat is shed from going through the radiator. Sorry if I muddied the water it's just something you can do to see how much cooling is happening with the radiator. Quote Share this post Link to post Share on other sites
danno 128 Report post Posted July 11, 2017 One more method to try. If the temperature sensor is like most, they have an output that is electrical resistance, and it changes with temperature. You have an ohmmeter, read the resistance on the temperature sensor with your meter. Then you need to convert resistance to temperature, which you should be able to get from the manufacturer. If you cannot, take the sensor off the car and put it in boiling water in your kitchen. That way you know exactly what the resistance is at 212F. Also measure the resistance at room temp. Plot a graph between 72 and 212 degrees to find out what the resistance should be at 190. Then when you measure the resistance with it installed back in your car, and plot it on the graph you created, you will know exactly. Takes a bit of work, but at no cost, and you know it is correct. 1 JayEstes reacted to this Quote Share this post Link to post Share on other sites
69volunteer 84 Report post Posted July 11, 2017 I had a similar issue when I first re-wired my car. I used the AAW wiring harness but used multiple version of a re-production temp sender. They all said the car was running hot. Not pegged to H but close. I used my infrared gun and at multiple points on the engine was around 180. I finally found a NOS temp sender on ebay and replaced. Gauge reads right in the middle. 1 JayEstes reacted to this Quote Share this post Link to post Share on other sites
rittenrotton 4 Report post Posted July 12, 2017 Thank you all for your help/suggestions! I got a non-contact infrared thermometer and I going to use that first. I might also try the boiling water trick to test my gauges and temp sensor. I'm hapoy to hear that I'm not the only one who had trouble with their temp gauge after rewiring the car with the aaw kit. I have a feeling that I will most likely have to replace that sensor. But we will see and I'll keep you all posted. Quote Share this post Link to post Share on other sites
RPM 1,278 Report post Posted July 13, 2017 A guy who answered the phone at Auto Meter said their gauges require the use of their sending units. Fact or fiction, who knows? Quote Share this post Link to post Share on other sites
Brian Conway 283 Report post Posted July 13, 2017 FWIW; All stock set up. Brian Quote Share this post Link to post Share on other sites
moodster 55 Report post Posted July 13, 2017 Stock should be about 192 degrees. I'm unsure what the coolant temperature would read at the radiator but I think it would be cooler than what it would read in the block. I have the stock thermostat and my Speedhut gauge with digital sending unit reads around 195 degrees most of the time. david Quote Share this post Link to post Share on other sites
Mach1 Driver 632 Report post Posted July 13, 2017 1 hour ago, Brian Conway said: FWIW; All stock set up. Brian 182F vrs 29.4 what? Even in C it would only equal 84.9F, so what is the significance of the meter? I'm missing something. Quote Share this post Link to post Share on other sites
Brian Conway 283 Report post Posted July 13, 2017 The meter reading is at the sending unit located in the intake manifold. Brian Quote Share this post Link to post Share on other sites
Mach1 Driver 632 Report post Posted July 13, 2017 Hmm, must be German, as in Kaput! Quote Share this post Link to post Share on other sites
Bob & Sue 110 Report post Posted July 13, 2017 Done some sender checking with Teleflex gauges they're all tested the same way any sender must contact water and have a good ground no teflon tape or thread sealer must be metal to metal to be accurate. You'll need to contact Vintage for their specs. this is from Auto Meters FAQ's. The proper method to test one of these gauges is in a pot of hot water. Set the sensing probe fully into the water, and monitor the water temperature with the gauge and also with a known good & accurate thermometer. Of course use extreme caution when dealing with any hot fluids. Also, knowing that water boils at 212 degrees F (at sea level) may give you an indicator as to the accuracy of the gauge in question. Mechanical temperature gauges do not utilize a replaceable sender, and are typically not repairable. Therefore, do not attempt to remove the capillary tube or sensing bulb for any reason. Checking the accuracy of a short sweep temperature gauge (one that uses a single terminal sender): This gauge typically has 3 terminals on the rear of the gauge (not including the light connections). It sends a signal out to the sender from the “S” terminal, and it is the senders job to vary this signals resistance to ground. With this said, for a sender and gauge to operate, then sender must be threaded into something that is grounded since the ground path for the sender is actually the sender mounting threads. The gauge itself really is nothing more than a fine tuned & calibrated ohm meter. To check the gauge, you will need a controlled and measurable resistance to ground source. Many shops that deal with automotive electrical repair have what is called a gauge tester, which is really a switchboard with different resistance values. The Auto Meter 100 to 250 degree, short sweep temperature gauge uses a specification of 1123 ohms of resistance to ground to = 100 degrees F, and 65 ohms of resistance to ground to = 250 degrees F. You may contact our Service Department for further specs. Read more at https://www.autometer.com/resources/index/faq_view/id/11#1tIQzlZ7Qpjorcub.99 Quote Share this post Link to post Share on other sites
Midlife 840 Report post Posted July 14, 2017 9 hours ago, Mach1 Driver said: 182F vrs 29.4 what? Even in C it would only equal 84.9F, so what is the significance of the meter? I'm missing something. 29.4 ohms. Quote Share this post Link to post Share on other sites
Bob & Sue 110 Report post Posted July 14, 2017 11 hours ago, RPM said: A guy who answered the phone at Auto Meter said their gauges require the use of their sending units. Fact or fiction, who knows? All gauge manufacturers use either a stock type sender or require you to purchase theirs. Their gauge is reading the ohms that pass to like the one pictured it reads 29.4 ohms if that were hooked up to an Auto Meter it would probably read 250 degrees because the gauge is 100-250 degrees. 1 RPM reacted to this Quote Share this post Link to post Share on other sites
rittenrotton 4 Report post Posted July 14, 2017 Wow! Thank you everyone for all the great suggestions/help! Knowing now that the autometer gauge requires the use of their sending unit would explain why it's off (or so I think). I checked the motor with my new Infrared thermometer gun and found that the motor is running at about 180 +/-. I'm going to check the voltage and use the thermometer in the radatior as Mach1 driver suggested just to double check. It seems the new vintage gauge was correct and working correctly but it doesn't hurt to double check. Quote Share this post Link to post Share on other sites
Mach1 Driver 632 Report post Posted July 14, 2017 18 hours ago, Midlife said: 29.4 ohms. Oh well that's what I missed, HA! That still doesn't tell you much, since there doesn't appear to be a chart that gives ohms vrs temp. I suppose it doesn't exist, since none of the Ford gauges readout in *F, but low and hi. I did a search and found an chart by a guy that lives at 6150 ft where water boils below 200F. Also, since the range of the sensor is supposed to be from 10 to 73 ohms, I don't understand all the readings above 100 ohms. He tested and charted 3 temp sensors for a 66 Mustang. Surprisingly they are fairly linear. https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&uact=8&ved=0ahUKEwj6qeGPsInVAhUENz4KHbaOBkoQFggoMAA&url=http%3A%2F%2Fwww.allfordmustangs.com%2Fforums%2Fclassic-tech%2F204666-temperature-senders.html&usg=AFQjCNFGVQbcPYLiEQdkTVrw-V782b7N1w Quote Share this post Link to post Share on other sites
