Re: Oil pump change on 56 Packard 400

Posted by HH56 On 2023/10/3 12:05:45

Verify the sender is for use with gauges and not idiot lights. Some senders look much alike but idiot lights only use an on/off switch while gauges need a resistance change. The Napa website used to give some specific pressure resistance readings with a given sender but Napa has changed their site and eliminated all that good info to the point it is almost worthless today. The proper sender will have a range of approximately 70 ohms at the 0 pressure end will move to about 10 ohms at 100 psi. Won't be easy to measure the high end but maybe place a meter between the terminal and base fitting to see if it reads somewhere around 70 ohms just sitting.

For a correct pressure reading the sender can be mounted at any point in the oil system that direct pressure out from the pump can be measured. As far as I know there is no restriction on how the sender is positioned when mounted. What the senders do need is an excellent ground. Believe I see some Teflon tape on the extension nipple. Possibly the tape is affecting the sender ground to the point it is not able to produce a decent resistance reading to the gauge.

As a temporary check to rule out a ground issue bare a few inches of 16ga jumper wire and wrap a few turns around the threaded metal port at the sender base. Be sure it is directly on the sender and not any of the extra piping. Attach the other end to a known good ground. If the gauge works reliably then do something with the tape on the extension pieces.