Canister Type Oil Pressure Senders

These senders are on the Cortina GT 10/64 > 9/66. Ford p/n : C5EH-9D290B or C9EH-9D290A. 
80 psi ( stamped near the brass base ).

Function:

The oil gauge has 5 volts applied from the voltage stabilizer to one terminal the other terminal connects to the sender which acts as a variable resistor to ground.

64-66 Cortina MK1 GT Oil Sender Unit

Canister plus spring loaded plunger base cut off to expose circuitry and diaphragm

Completely disassembled unit.

As the motor is running, engine oil enters the sender and pushes against a rubber diaphragm in turn forces a spring loaded plunger to move a sweeper arm across a wire wound variable 80 - 0 ohm resistor. Oil pressure causes the 80 ohm resistor to decrease in value thus the oil gauge needle will move towards the right.
It is possible to refurbish these sender units by carefully cutting off the canister body midway around with a hack saw ( I've destroyed my sender to remove all the parts of the unit ) This will expose the internal circuitry for cleaning and damage. Oil inside the canister is an indication of a ruptured diaphram at that point the unit is unserviceable.
Carefully clean the sweeper contact, wire wound resistor and arm contact to the threaded stud. Connnect an ohm meter across the resistor, it should read approx. 80 ohms. With the ohm meter still attached across the resistor, move the plunger arm slowly so that the sweeper moves across the resistor. Resistance will decrease from 80 ohms to approx. 0 ohms without hesitation. Thus 80 ohms = 0 psi and 0 ohms = 80 psi.
Realistically the resistor should read around the 40 ohms for 40 psi. as the car is running at speed. If it works properly, the canister can be soldered back on the unit with 50/50 type solder. Don't use a torch.

Replacement senders:

Ford/Lincoln/Mercury 1960 - 80 canister senders 1/8" x 27 NPT ( for a 1/4" hole size ) approx. 80-90 psi
with a terminal button is close enough and should work.