Posted by: Mark Polk | 2015

71 Power Wagon – Water Temperature & Eelectric Fan Sending Unit Issues

Poly 318 upper radiator hoseWhen I rebuilt the poly head 318 engine for the 70 Power Wagon project I added an Edlebrock P600 6-pack manifold with 3 Rochester carburetors. At the time I didn’t think about needing access to water jackets in the manifold for additional temperature sending units. The old gauge cluster required one water temperature sending unit for the electric water temperature gauge and the P600 intake had one threaded hole for a sending unit.

It wasn’t until I decided to add an electric fan and mechanical water temperature gauge into the mix that I realized I had a problem. I need two sending units, but only had one space in the intake to install them. When it comes to water temperature sending units I prefer to install  it in the intake manifold as close to the thermostat housing as possible for accurate readings of the water temperature in the engine. My thoughts are if you put the sending unit at the radiator you get a cooler temperature reading because, number one it’s at the radiator not the engine, and number two you get a temperature reading after the thermostat opens.

This is more of a concern for the electric cooling fan than it is for the water temperature gauge because the cooling fan is designed to come on and turn off at a set temperature.  If the water is cooler at the radiator the cooling fan could possibly come on and stay on if the water temperature, which is somewhat regulated by the thermostat,  does not drop low enough to turn the fan off. A bigger problem could be the water at the radiator never gets hot enough to turn the fan on in the first place.

Because of these concerns my plan was to install the cooling fan sending unit at the intake manifold, but the threaded hole was too small for the sending unit threads. I have not looked into adapters yet, or the possibility of replacing the sending unit with one that has the same temperature settings but smaller threads. This leaves the only option for installing the mechanical temperature sending unit at the upper section of the radiator or by splicing into the upper radiator hose using a hose adapter that has a welded bung adapter for another sending unit.

I am still trying to sort this out in my mind and will keep you posted on what I figure works best to sovle the problem.

Next up:  Fabricating a Roll Pan

Read about the full build HERE

Mark Polk

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