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Alternate placement for a temp gauge sender:
Revised 24 July 2011 to add better temp sender location description and the necessity to loop the fluid flow through the heater circuit.
How it works:
If you want any kind of operation similar to stock, the ECT/heater feed line is the best place for a temp sender or fan thermo sensor. After all, the computer uses the ECT to pick up data on how warm the engine is. Putting the temp sender in the same line as the ECT is a simple way to get the best possible accuracy at minimum cost and complication.
Some things to keep in mind:
Just be sure that you haven’t blocked the coolant return because of a leaky heater core. For this to work correctly, the coolant needs to flow from the ECT sensor tubing back to the water pump. That means a leaky heater circuit gets looped rather than just plugged up. Join the rubber hoses together with a hose splice from Home Depot rather than plug them up.
Where to put it:
Use the heater feed that comes off the intake manifold that has the ECT sensor in it. Cut the rubber hose that connects the manifold water feed to the heater and splice in a tee adapter for the temp gauge sender. That way you will get the most accurate temp readings since the coolant is always flowing through the heater circuit in a stock car.
Tee adapter info:
Make a pilgrimage to your local hardware or home supply center and get some copper pipe and a tee that fits the temp gauge sender. Solder two pieces of copper pipe onto a copper pipe tee with threads in the tee part. Find the correct brass fitting to match the temp sender threads to the tee fitting.
DYI answer to electric fan problems...
If you are good with electrical stuff (90% of the people here aren't), build your own controller. The numbers on the diagram (#86, #87, etc) refer to the numbers on the bottom of a typical automotive relay.
Note that the temp sensor in the diagram needs to match the thermostat in your engine. The preferred arrangement is to have it open about 5 degrees above the thermostat.
To allow the ignition switch to control the fan so that it does not run when the ignition is off, connect the relay contact #86 to the red/green wire on the ignition coil or to the red/yellow wire on the coolant level sensor.