Temp gauge w/electric fans

[wrkrbeee]

Hi everyone, bottom line here is the factory temp gauge pegs within about 60 secs of startup.  Why?  Well, I installed an Entropy radiator with dual electric fans on my big block 1969 Camaro SS.  Intake manifold/fuel line/heater hose fitting/temp gauge all created their own limitations for installing the Entropy temp sensor for the fans.  Settled with the following positioning: 1) removed heater hose fitting from intake manifold and replaced with factory temp sending unit (lower profile fits neatly under the fuel line); and 2) installed a t-fitting in place of the factory temp sending unit, which now houses the Entropy temp sensor and the heater hose fitting.  I'm not an engineer, but I'm pretty sure that the temp sensors measure resistance using an electrical charge introduced into the coolant.  And, my guess is that when you have two such temp sensors introducing their individual electrical charges, the factory temp gauge sorta freaks out (i.e., pegs the gauge).  Anyone have any insight for the temp sensor function?  And, anyone have any suggested remedies for the problem?  I am grateful for any comments.  Thanks!

[Mark]

Factory and all temperature sensors used in these cars are essentially variable resistors that change the resistance between the single wire connector and the shell of the gauge as the coolant temperature changes. Resistance starts high, and goes lower as the coolant heats up.  This changes the current flow in the gauge and the gauge moves upscale as the temperature increases, and down scale as the coolant cools off.  Because the gauge circuit relies on the engine block ground as part of the circuit, if you grounded the fans to the block, when the fans come on the voltage difference between the block and the battery voltage changes (becomes less) because of the current flow thru the fans raises the blocks voltage potential which screws up the gauge reading.  If the gauges going weird on you corresponds to the fans starting its a 99% chance that is the reason.  Run the fan grounds back directly to battery ground.

[wrkrbeee]

Thanks Mark!  That's good information on the temp sensor.  My gauge pegs shortly after startup, and I have the fans set to come on at 160 degrees (and with a 160 degree thermostat, the fans are coming on shortly after the upper radiator hose gets hot).  The temp sensor problem started using the old sensor, so I replaced it with a new one, and the problem persists.  So, the new sensor "could" be bad, but I'm thinking the more likely suspects here are wire gremlins.  Given that I've recently installed new carpet, which requires complete removal of the center console, wiring seems to be an even more likely suspect.  Nevertheless, thanks for the info Mark!