Ken,
I love hearing about Heralds as daily drivers! Mine will be too, one of
these days (just need to get that new top on...)
My Herald is a '62. My experiences with the temp gauge are similar to
yours. I have the advantage of having watched mine evolve over time, 30
years to be exact. It does interesting things like jump higher when the
headlights are turned on...
The temp and fuel gauges are electrical devices. Suggest you get a grip
on the electrical issues first. Both gauges are fed directly by the
ignition switch. There's a variable resistance element connected between
the downstream terminal of each gauge, and ground. Even if your gauge
and sender are working perfectly, behavior of the gauge is going to vary
with the battery / voltage regulator voltage, and any stray resistance
in the path back to the GND battery terminal. There are opportunities
for stray *variable* resistance in both battery terminals, the terminals
on the starter solenoid, the ignition switch, the threads between the
sender and the thermostat housing, the bolts between the thermostat
housing and the water pump housing, the engine grounding strap, and the
battery grounding cable. Reply offline if you'd like me to suggest
specific tests - I assume you have a multimeter.
There are also thermal design issues around the sender. It's a quite bad
thermal design, actually, as far as the temperature gauge is concerned.
The sender is mounted in an aluminum housing, it's directly behind the
fan and above the radiator, it's thermally insulated from the block by a
gasket, and it's after the thermostat. When the thermostat is closed,
you're reading is affected more by air temperature than coolant
temperature. And if you have a relatively high temperature thermostat,
it might never open very wide except on hot days, because the radiator
is so huge. This all conspires make the gauge reading extremely
sensitive when the coolant in the block is around the operating point of
the thermostat. It also means that if the 'stat sticks closed, the gauge
will show a nice cool reading while your engine quietly overheats. Been
there!
Suggestions:
1. Make sure the electrical aspects are good.
2. Calibrate your gauge - Idle your engine with the radiator cap off
till the needle gets as high as you've ever seen it. Make sure coolant
is flowing freely into the radiator, then measure its temperature with a
meat or candy thermometer. Mine reads 185 degrees F at the very high end
of the N range, with the headlights off:>
3. Put in a 160 degree thermostat.
4. In that order.
bk
Hre are my suggestions
Ken Gano wrote:
> 97 days, 7800 miles, the saga continues.
>
> I am still fighting a cooling problem. Notwithstanding two flushes and
> three different thermostats, I am getting erratic gauge readings. It either
> runs on the low end of the normal scale or the very high end and I see no
> real correlation. (Ambient air temperature seems to make a difference but
> it's not always related) Knock on wood, so far it has not gone over the top
> of the normal scale, but it gets close and we are just now going into the
> dog days of summer. I am beginning to suspect a bad sender or gauge.
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