Strange temp gauge behaviour in TR7 V8

[Maki65]

I am have a strange issue with my Triumph TR7 V8's temperature gauge. I recently had the head valve guide stem oil seals done and put it all back together. However, since rebuilding it the thermostat opens normally then settles where it should, then when up to reasonable speed 40/50 mph the needle starts to move up and then back down. It only moves a needles width or so but it has never done this before. I have checked the temperature with an infrared thermometer and I was getting around 70-75 degrees at both the stat housing and the transmitter housing, looks a little cool to me.

The things I have done so far:-
New thermostat (twice!) the first a genuine Unipart 82 degrees.
New Unipart temerature transmitter.
Flushed the system twice.
Checked the water pump.
Replaced the temperature gauge.
Rewired the temperature sensor to gauge.
Cleaned all the connection points on the Instrument Panel OCB.
Cleaned and remade all earths on the car
Checked the viscous fan for proper function. OK.
Tried an extra ground from the instrument panel to body.

None of the above worked. It is worth noting that my original stat had no jiggle pin and worked fine for years, the two newer ones have pins. The car is standard spec SD1 engine on SU's and tubular manifolds.

I realised that the car does seem to run on the cool side and am wondering if the 82 degree stat is to warm and a 74 degree stat should be used, as the gauge reading looks like it is trying to settle but cannot.

Any observations would be great many thanks.

[Ian Anderson]

It may seem strange question but have you checked your voltage both battery and after the voltage stabiliser that should bring it to 10v from memory for the instruments.

Obviously would need to be done when on the move so may be a tad difficult.

If the voltage fluctuates I would suggest trying a different battery as if it is dying it will ask for varying amounts of charge current and this will move the voltage….. move voltage and your meter will move (after all it is only a volt meter with a different scale)

I had purchased a led volt meter that pushed int the cigarette lighter….. it showed voltage to 1 decimal movement and moved a couple of bolts not long before my battery gave up the ghost. Gt40 used in summer laid up for long periods over winter so battery was “tested”

Ian

[Maki65]

Thanks for the reply Ian. Unfortunately the TR7 does not have a voltage stabiliser for it's gauges. Earlier TR's did but not the 7. Tha battery is not that old and I use CTEK MXS 5.0 to trickle charge over winter. All the other electrical items in the car are all operating as they should.

I may well revert back to a stat that I know did work and then go from there, or a cooler stat and see if that works. Very frustrating indeed!

[Ian Anderson]

Hope you did not use ptf tape on the threads of the sender…. It may have slightly intermittent contact

[Maki65]

No PTFE tape on the threads just the included washer.