Ahoy All,
My ancient sender packed up and left my gauge needle pinned to the right. I looked in to buying a replacement but was shocked to discover that they are ludicrously pricey for what they are and come with a 1/8" NPT thread which means you also need an M14 x 1.5 adapter. There must be an alternative thinks I. And so I went down the Smiths instrument rabbit hole... Again!
What I discovered is that Smiths gauges (unlike most) have a range of resistance from 240 Ohms (0 on the gauge) to 33 Ohms (100 on the gauge). As well as the importance of matching the resistance it's also important to mate the range. The smith gauge on the Renault engines cars has a 0-100 psi range or 7 bar.
After much trolling of various forums I discovered that a Lada Niva has a very similar sender, the only difference is that it is for an 8 bar gauge. Close enough I figured and since it was a sixth of the price of a Smiths one, took a chance. Because the sender is an 8 bar and not a 7 bar I added a 477 ohm resistor to reduce the resistance a little to try and match the original gauge. The gauge is wired as normal but an additional wire is taken from the same point on the sender through the resistor and grounded to earth. This has the effect of raising the pressure shown on the gauge at the cost of some slight sluggishness.
So, although not as good as the original set up it does at least work and show pressure and perhaps more importantly it will also show when there is no pressure. And this sender even has the correct 14 x 1.5 thread so needs no adapter.
For those who wish to try this themselves a 477 ohm resistor has the following colours: Yellow, Violet, Black, Gold. Yellow = 4, Violet = 7, Black is a multiplier and Gold = 5% tolerance. You can fit the resistor around either way.
The part number for the Lada Niva oil pressure sender is 2103-3810300-01
Cheers
