On Sat, May 27, 2017 at 2:45 PM, George Gaudette <gcgaudette@gmail.com>
wrote:

> Hi Volks,
>
> '90 water-cooled automatic camper here.
>

Thank you. :)

>
> My coolant temp needle stopped moving entirely some time ago.  The coolant
> blinky light works normally (blinks initially on startup then goes out, and
> has recently blinked for low coolant level).
>

Good.  Gauge doesn't have leaky timing cap, and coolant level controller is
successfully simulating overheat in short pulses that activate the blinker
but don't materially affect the gauge itself.

>
> ...which is to say I hoped to validate that the temp gauge is in working
> order (including the wiring to it).
>
> The first thing to do was to check that there is 10V across those wires.
> Instead I found there was about 4.9V.  I tried with the negative lead
> touching a ground point instead of the brown wire, and got 5.3V.
>

The ECU supplies five volts to Temp-II through an ?8132 ohm? resistor,
creating a voltage divider with the variable resistance of the Temp-II
sender.  This however has nought to do wi' t'gauge -- the problem there is
that one of the fly rods has outta skew on t'treadle.  Or more likely that
the sender or connector is open, of course.  It's the black one around the
corner from the blue Temp-II sender which is concerned strictly with engine
operation.  265 ohms to ground should give you the bottom mark, 35 ohms the
beginning of overheat zone and blinking light (light threshold is around 42
ohms IIRC).  Grounding the sender lead should make the gauge go up like a
slow rocket, and if you leave it connected, start smelling hot in a minute
or two.  No action means either a wiring problem between engine bay and
gauge (but not the panel connector or panel wiring since the low coolant
warning functions) or -- very very unlikely, the gauge heater has gone open
or the needle suspension has failed.

Yrs,
d