Hot or not?

Encouraged by all the enthusiastic comments on the overdrive question, I take the liberty to post another question.
The temperature of my engine was always very stable, even in a traffic jam. About a month ago, the temperature suddenly dropped and even during warm days it hardly reached the 65 degrees Celsius. Yesterday, I measured the cooling fluid temperature, which appeared to be 65-70 degrees after a 15 minute drive (seems OK), but the temp. gauge indicated about 50-55 degrees. So I assume the gauge is not correct. Is there a better way to test the gauge and is there a way to adjust the gauge? Or does anybody know what might have caused the sudden change in indication of the gauge?
(I can not find an answer to this question in the manual).

Thanks,

Rienk /ubbthreads/images/graemlins/driving.gif

Rienk - here's a path you might take.
The gauge works by taking in a voltage on one side, and attempting to ground it on the other, through the sending unit.
There is a wire from the fuse box to the voltage stabilizer, that then goes to both temperature and fuel gauges. If the stabilizer is bad, then both of those gauges will read incorrectly. If not, the wire from the stabilizer to the temp gauge may be loose or bad (hard to go bad, but very easy to become loose.)
The sending unit, near the thermostat, is a thermister. Power goes through the gauge, through the sending unit, to ground. The thermister works this way - as an old GM instructor taught us, it's just like your girlfriend was in school; the hotter it is, the lower the resistance. So, if the wire from the gauge to the sender is loose or corroded, you will have too much resistance, and therefore a low reading gauge.
I use a variable resistor (rheostat) from a local electrical supply shop (0-100K ohms), and substitute it for the sender. Simply by twisting the dial, I can see if the gauge is capable of moving the full sweep. If so, I replace the sender. If not, I begin to check for wires.
Triumph did not provide us specifications for the sender, so one can only guess, but I've had good luck with this little tool on many cars over the years.
Odds are you'll find the wire at or near the sender unit to be in bad shape, and likely a new connector, clean and dry, will cure your trouble.
Good luck, and let us know how you make out.

Thanks Paul!
Good teacher that MG instructor, now I will never forget /ubbthreads/images/graemlins/smile.gif
The fuel gauge seems OK, and I already inspected the wire from the thermister and it also seemed OK. But I will follow your instructions and properly check the gauge and the wiring. Unfortunately I will not be able to work on the TR before this weekend /ubbthreads/images/graemlins/frown.gif. So I will let you know if I solved the problem as soon as I am able to check it.

Cheers,
Rienk

I had the same exact problem, and it was a bad sending unit. It's about a $7 fix and takes 10 minutes.

Hi, this weekend I also checked the gauge with a variable resistor. The gauge seems fine, so I assume it is a bad sending unit (as also mentioned by Steven). I better emigrate to the States, because the same unit costs about $15 overhere (although we are much closer to the UK) /ubbthreads/images/graemlins/grin.gif.
I will let you know if it solves the problem, but that may take a while. Because the Triump garage is not close by, it will take some time before I can buy the unit. Until that time I will use my bare skin to see if the engine is hot or not.... /ubbthreads/images/graemlins/crazyeyes.gif

Cheers,
/ubbthreads/images/graemlins/driving.gif
Rienk

Hi Rienk, sometimes we tend to look at the little black boxes as the cause of all our problems, so what may be out of line in the way everyone one else is thinking, try this. Most TR owner's are always trying to keep their car cooler and add all kinds of thermostats with varying ranges. I know it's a pain in the butt to get it out, but it sounds as if you have a stuck thermostat or maybe even a broken one, sometimes one ear will brake off and leave it half open. A lot cheaper than a sending unit but you will waste a bit of coolant. Wayne

you have to change thermostats with the seasons....My TR6 was running hot for years on a standard thermostat in summer. Just on a whim I changed to a summer t stat....and it's been running fine ever since.