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TR2/3/3A TR3 Op temp issue and mechanical gauge

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prb51

prb51

Luke Skywalker
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Gents/Ladies,
I posted a thread a few days ago about my cool temp operating TR3.
I changed thermostats suspecting a failed (open position) stat.
While everything was apart I retested my mechanical gauge (rebuilt 4 years ago by a reputable rebuilder) and found it to be off, way off.
I do not blame the rebuilder as I tested it aginst multiple sources on arrival and it was DB's on.
Presently the gauge indicated 90 degree line is actually 172 degrees. A huge variation. Tested and retested.
I was unaware the gauges could vary so much...I thought they worked or didn't work as nothing has really happened to the 'system'.
Anyway, my 'cold' running TR3 is actually spot on.
Live and learn.....I suspect if this one goes south I'll convert to an electrical unit and make it look stock.
Time to check the oil pressure gauge.
 
Mechanical gauges have a whole raft of things that can go wrong internally, and still move the needle. Including just plain old age, as there is a metal element that flexes as the needle moves.

Still might be work contacting the rebuilder, to see if they will give you a break on repairing it. In the meantime, something like this
https://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=370089961595
or this
https://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=280277857307
would let you drive the car. They fit the original holes, just need to wire up the dash light.
 
Oh, I'm going to drive the car. I tested/retested the gauge and now know where 160/172/180/185 degrees register so I'll be ok as long as the gauge doesn't deteriorate anymore. It seems to be holding steady as is for whatever reason.
Doesn't the TR4a have a similar gauge face (flat glass) but is an electronic unit? I'd rather go that route.
 
prb51 said:
Doesn't the TR4a have a similar gauge face (flat glass) but is an electronic unit? I'd rather go that route.
Click to expand...
Not "electronic" exactly, but electrical, yes. The early TR4 units look nearly identical to the TR3. Though it's doubtful if they are any more accurate; they certainly are more rugged and easier to adjust.

Don't forget, you'll also need a voltage stabilizer.
 
"Don't forget, you'll also need a voltage stabilizer".....
What is a voltage stabilzer (stabalizes current?) and how does it relate to the electric gauge?
 
Well, "voltage stabilizer" is a bit of a misnomer; but it's what Lucas chose to call the device that compensates for changes in battery voltage between discharge (eg sitting at a stop light with the headlights on) and charge (running down the highway). There's a nice photo of one over here.

The can needs to be grounded, the 'B' terminal gets power from the ignition switch (green wire), and the 'I' terminal supplies power to the electric gauge. Without it (or if it fails), your electric temp gauge will read way high.
 
Here's a snippet from Dan's schematic that might help clarify.
 
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