On my last drive I noticed that the Oil pressure dial on my 1976 Alftetta is dead, (used to work fine with expected strange Alfa behavior).
So did couple of tests, first I disconnected the wire coming from the oil pressure sender and verified that the dial works by shortening the wire to the ground, it does so nor problem with the instrument panel.
Next, I measured the resistance of the sender, from its output to the vehicle ground, the results were ~1.5MOhm, this is Bad, in addition I see signs of Oil leak around the sensor so it looks like this sensor is dead.
OK so what type of oil pressure sender do I Need to order? the dial provides a reading of up to 100~110 LB/S (I Assume its equivalent to 100PSI), a common oil reassure senders for 100PSI are available with two types of common resistance values, the most popular one being 10-160 Ohm and the 2nd is a 33-240 Ohm, the high number is the resistance when no oil pressure is found, the low number is the resistance when the sender feels its max specified pressure range (100PSI).
To verify and find which of these two ranges will work best and what is the optimal resistance value I tried a combination of resistors and simulated the two sensors.
The 10-160 Ohm type will rest spot on “0” when ignition switch is turned “ON” but will only go half scale ~55PSI with engine running and sensors reporting a full 100PSI.
The 33-240 Ohm type will sit at around 15PSI on switched ignition and around 80PSI when full 100PSI is reported by the sender.
None of the two is perfect, with a little more play I found that the ideal resistance value for spot on 0 on Ignition “ON” and full 100Psi oil measurement with Full scale for Alftetta oil pressure gauge is:
~ 10-300 Ohm.
I did find a vendor in Australia that sells a sender with above range (see link below), another decent alternative could be a 20-288 Ohm which can also be found.
Couple of comments:
Most of the general use oil pressure senders use a 1/8NPT connection so a M10 to NPT adapter is required.
Some of the oil senders has an additional switch inside for turning an OIL pressure alarm warning light not available o Alftetta.
Thx
Samuel.
10-300Ohm sender
![Image]()
So did couple of tests, first I disconnected the wire coming from the oil pressure sender and verified that the dial works by shortening the wire to the ground, it does so nor problem with the instrument panel.
Next, I measured the resistance of the sender, from its output to the vehicle ground, the results were ~1.5MOhm, this is Bad, in addition I see signs of Oil leak around the sensor so it looks like this sensor is dead.
OK so what type of oil pressure sender do I Need to order? the dial provides a reading of up to 100~110 LB/S (I Assume its equivalent to 100PSI), a common oil reassure senders for 100PSI are available with two types of common resistance values, the most popular one being 10-160 Ohm and the 2nd is a 33-240 Ohm, the high number is the resistance when no oil pressure is found, the low number is the resistance when the sender feels its max specified pressure range (100PSI).
To verify and find which of these two ranges will work best and what is the optimal resistance value I tried a combination of resistors and simulated the two sensors.
The 10-160 Ohm type will rest spot on “0” when ignition switch is turned “ON” but will only go half scale ~55PSI with engine running and sensors reporting a full 100PSI.
The 33-240 Ohm type will sit at around 15PSI on switched ignition and around 80PSI when full 100PSI is reported by the sender.
None of the two is perfect, with a little more play I found that the ideal resistance value for spot on 0 on Ignition “ON” and full 100Psi oil measurement with Full scale for Alftetta oil pressure gauge is:
~ 10-300 Ohm.
I did find a vendor in Australia that sells a sender with above range (see link below), another decent alternative could be a 20-288 Ohm which can also be found.
Couple of comments:
Most of the general use oil pressure senders use a 1/8NPT connection so a M10 to NPT adapter is required.
Some of the oil senders has an additional switch inside for turning an OIL pressure alarm warning light not available o Alftetta.
Thx
Samuel.
10-300Ohm sender
