RPM 1,190 Report post Posted May 26, 2016 I have an Auto Meter electric water temp gauge unit along with an electric Spal radiator fan. Any reason why I can't use one sending unit for both the oil gauge and fan relay? Ya I know, rookie question. But I got the good looks and my brothers got the brains. So I got that going for me, which is nice. Edit: Oil gauge is in error, it's the water temp gauge I'm talking about. 1 mandyse1 reacted to this Quote Share this post Link to post Share on other sites
Midlife 814 Report post Posted May 26, 2016 Your oil gauge will only read when the fan is on. Am I mis-understanding what you're trying to do? Quote Share this post Link to post Share on other sites
Mach1 Driver 560 Report post Posted May 26, 2016 First you said "water temp and fan", then "oil gauge and fan" It doesn't really matter- oil, water, and fan don't mix. The sender will be some kind of variable resistor, the fan needs a snap action switch that opens and closes at specific temperatures. Quote Share this post Link to post Share on other sites
RPM 1,190 Report post Posted May 26, 2016 Oops, sorry bout that. I'm blaming a long day and age :) It's not the oil gauge, but the water temp. So if I understand it, the fan sending unit which screws into the intake manifold is a switch which turns the fan on/off at the preset temps, and the water temp sending unit provides constant voltage to the gauge. Quote Share this post Link to post Share on other sites
SM69Mach 68 Report post Posted May 26, 2016 I don't think that will work as the gauge and the electric fan operate differently I believe. The Electric fan is usually an on/off based on the temp of the coolant. The gauge needs different output for the gauge to work properly. I actually had to change my gauge sensor when I went from the autometer single gauge to the Dakota Digital gauges. I was told the gauges were calibrated for the that particular sensor. Not sure if that is true or not, I didn't test the theory. Quote Share this post Link to post Share on other sites
RPM 1,190 Report post Posted May 26, 2016 Thanks guys. Quote Share this post Link to post Share on other sites
schweigert 13 Report post Posted May 27, 2016 are you gonna hook up the fan switch right to the battery? thats how i have mine and it will run the fan even when the car is off for a bit.... not sure if i like it or not. I've had people stop me and say "hey your car is still on". Quote Share this post Link to post Share on other sites
Mach1 Driver 560 Report post Posted May 27, 2016 It's not the oil gauge, but the water temp. So if I understand it, the fan sending unit which screws into the intake manifold is a switch which turns the fan on/off at the preset temps, and the water temp sending unit provides constant voltage to the gauge. You've got the idea of the fan correct and I think you "get the drift" on the water, but let me expand. With the key on you get +5v to the water temp meter. Current flows through the meter to the sensor. When the sensor is cold it has about 78 ohms resistance and 10 ohms when hot. More current can flow through the sensor to the chassis when the sensor has less resistance- when it is hot and that makes the meter register higher. Its basically an ammeter with a scale made to show water temp instead of amperage. You can see why this wouldn't do much for the fan, since it needs the power either on (zero resistance) or off (infinite resistance). Quote Share this post Link to post Share on other sites
