temperature gauge issue

hiya. been absent for a while. got my self a nice new landy - series 3, 1975, lwb station wagon, 2.25 petrol.
one of the many problems is that the temperature gauge seems to shoot up incredibly quickly.
after 90 seconds of idling the gauge is about a third of the way up. if i leave it idling it doesn't go much above two thirds after fifteen minutes, but if i drive into work (4 miles) then it's quickly on the red.

the water in the rad is a nice green colour, and gets hot, eventually it iwll even steam slightly (20 minutes or so) and the heater pipes get hot if i open the valve, but looking down into the rad it doesn't look like there is much flow (if any) - i was under the impression that once the thermostat opened this should look like niagara falls. not having driven it more than 20 miles in a go it hasn't yet overheated.

so i think i've got one of four possible problems
1. crap gauge - other electrics are dicky, so it wouldn't come as a surprise, and this is my favourite choice.
2. knackered thermostat - but then why would the rad water heat up if theres no coolant circulating?
3. knackered pump - same objections as 2.
4. partially blocked system - don't like the sound of it, but the fact that the coolant is still nice and green and there is some water flowing lends this as a possibility.

what do you reckon?

Possibly just the temperature sender unit??? In my experiance the gauges seem fairly hardy, faults usually lie in the voltage regulator, sender unit or wiring conections in between......

dang. after idling it for half an hour yesterday lunchtime the gauge went up to half way and stuck there on the way home. coming in to work this morning it went about a fifth of the way up before i'd even pulled off, got up into the red over the next two miles, and then dropped back to halfway in the next four hundred yards.

electrical, surely?

check the earth contact on the regulator - give it a good clean.

magic, ta.

so long as it gets me to bedford on monday - i got a bricklaying course for my birthday.

With the IGN ON, pull the wire off the sender, and earth the wire to something.

The temp gauge should rise smoothly and go right off the scale.

If it does, suspect the ender needs binned and replaced.
If not ..... chances are the problem is at the dash end.

Your symptoms sound OK really.

But to ease your mind why not take out the thermostat,

1. make sure it is fully shut when cold.
2. make sure it has a jiggle pin so air bleeds out. If it does not, just drill a small hole 3 - 4 mm in the stat to the side of the disk.
3. put the stat in a pan, cover it with water, and light the gas under it. The stat should go wide open shortly before the water boils.

CharlesY

got to bedford and back without overheating. all the way there stuck on red, all the way back never went above halfway... guess it's the voltage regulator.

another dial to ignore on the front, then.