Testing oil pressure units

1966 Mk2. I want to test both my gauge and sender before trying to build oil pressure in a freshly-built engine. The engine is out of the car, so this should be easy.

Using some multimeter techniques I learned from American cars on YouTube…

  1. I took the brand new sender (made in the UK; from SNG) and applied the negative lead to the threads and the positive lead to the terminal, set the Ohms to 20k and I get 1. I understood that I should get 0. I get the same readings no matter which Ohm setting I use. Does this mean that the new sender is bad, or I’m doing something wrong?

  2. On the bench, I connected a negative lead from the battery to the mounting posts on the oil gauge and a positive lead to one of the connections on the back of the gauge. Nothing happened. Same result with both connections. The needle should move. Does this mean the gauge is bad, or I’m not testing it correctly?


With no pressure at the sending unit, resistance through the sending unit should be very high. So no current flow through the circuit with no oil pressure. A thousand ohms should be good at no pressure. I would put some compressed air on it (maybe 30 psi from a known source) and test it that way.

Your second test would ruin your gauge if left for more than a second. Basically shorted your battery through the gauge. I wouldn’t try that one again. If the gauge really didnt move with that test, the gauge was already toast.

The Smiths senders and gauges at this time were quite unique and not comparable to those produced by other manufacturers. In particular, the sender contains a mechanical voltage regulator, and operates as a pulse generator rather than a resistor. The gauge converts current pulses transmitted through the sender to heat, which then moves the needle via a bimetallic strip.

Much is in the archives, including testing. Search “smiths oil pressure sender” or similar. Good luck!

Have a look through this

I tested mine with the engine in the car and running at different RPMs with warm oil. The readings from the mechanical gauge were so different than the Smiths sending unit connected to the dash gauge I finally gave up on the electric gauge and fitted this mechanical one from Quality Classic in the UK, which is accurate and finally, after 50 years of ownership I have a accurate reading.

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