The old-style real oil pressure sender

http://digitalpics00.no-ip.org/~halatos/MazdaOPSender

For those who might be interested, I think you can probably repair one
of these expensive gadgets, in-car, if it is just intermittent or
reading low on the dash gauge.

I cut my old one open for a failure analysis and took pictures. The
wiper arm and the resistance winding were both undamaged, the main
issue was that the winding was dirty. Too much resistance makes the
gauge read low on the dash. I was able to test the gauge with a
potentiometer before I spent the $164 on the new sender, and the gauge
was not at fault. I suspect the gauge rarely fails, as it is rather
protected being inside the passenger compartment.

I suspect that the rubber boot around the can plays a large part of
why this happens. The canister around the workings of the sender is
open to the atmosphere, surprisingly. The rubber boot is there to
provide a high-resistance path to dirt and grime, but over time it
does not keep everything out. The fact that the resistance winding is
apparently lightly greased from the factory means any dust in the air
moving in and out of the can collects on the windings.

There is a vent hole in side of the metal can that could be used to
spray in some electrical or brake parts cleaner and get the connection
between the wiper and the resistance winding cleaned up. It might save
you $164.00 to try that first if your gauge is not working right.

Good luck with it.

Chris

Hal wrote:
> http://digitalpics00.no-ip.org/~halatos/MazdaOPSender
>
> For those who might be interested, I think you can probably repair one
> of these expensive gadgets, in-car, if it is just intermittent or
> reading low on the dash gauge.
>
> I cut my old one open for a failure analysis and took pictures. The
> wiper arm and the resistance winding were both undamaged, the main
> issue was that the winding was dirty. Too much resistance makes the
> gauge read low on the dash. I was able to test the gauge with a
> potentiometer before I spent the $164 on the new sender, and the gauge
> was not at fault. I suspect the gauge rarely fails, as it is rather
> protected being inside the passenger compartment.
>
> I suspect that the rubber boot around the can plays a large part of
> why this happens. The canister around the workings of the sender is
> open to the atmosphere, surprisingly. The rubber boot is there to
> provide a high-resistance path to dirt and grime, but over time it
> does not keep everything out. The fact that the resistance winding is
> apparently lightly greased from the factory means any dust in the air
> moving in and out of the can collects on the windings.
>
> There is a vent hole in side of the metal can that could be used to
> spray in some electrical or brake parts cleaner and get the connection
> between the wiper and the resistance winding cleaned up. It might save
> you $164.00 to try that first if your gauge is not working right.
>
> Good luck with it.
>
> Chris

Thanks for that.
I've got an intermittent sender in an old Nissan (diesel TD42), but from
the outside the design looks much like the MX5 sender, except it's a
combined unit with an on-off switch for the warning light as well as
potentiometer for pressure. The new OEM replacements have a different
vent system with a small diameter rubber hose hanging down a few inches
under the sender unit. Price is similar, and it's a common problem. It's
disturbing to see the oil pressure gauge swinging around even when I
know the reason and there is the backup of a warning light.
Next oil change I'll try spraying inside the vent.