Smiths Electric Temperature Gauge

[karls59tr]

I'd like to upgrade the temp gauge in my TR3 to one of these units. Anyone know how they operate in terms of where they would connect to the cooling system? It wouldn't use the same gas filled tube system as the original but what would it use?

 

[Andrew Mace]

Normally, they'd use a sending unit, which would locate pretty much exactly where the original sender/tube would go. And most all of the electrical gauges (at least those from a TR4 to more or less match your other gauges) would have a voltage stabilizer in the circuit as well.

 

[karls59tr]

Some time ago I mentioned on his forum about an experience I had with my TR3 overheating. The bypass hose had blown but I hadn't realized it until I popped the hood some time later. I had lost about a gallon of coolant but the temp gauge never registered the higher temperature! I removed the gauge and tested it in boiling water and the gauge registered the higher temp. Any ideas on why the gauge wouldn't register when it was really needed? If the bypass hose blows and there is no coolant surrounding the gas tube then the gauge isn't going to register the coolant loss.Is this correct?

 

[TR3driver]

Well, the bulb certainly has to get hot for the gauge to read hot. But even without liquid coolant in the thermostat housing, it would still get hot by either conduction through the metal, or by the steam going by (assuming there was any coolant at all in the engine).

Last time I popped a bypass hose, the engine never did actually overheat. Instead the hose sprayed coolant all over and I pulled over for the water coming out of the vents in the hood. I'm guessing that something similar happened to you.

PS, the same problem applies to the electric gauge; the bulb of the sending unit has to get hot for the gauge to read hot.

 

[TR3driver]

And most all of the electrical gauges (at least those from a TR4 to more or less match your other gauges)

Indeed, the early TR4 temp gauge looks nearly identical to the TR3 gauge. And as Andy notes, the sender screws into the same hole; and you need a voltage "stabilizer" in the circuit.

However, aftermarket gauges usually don't require a VS, so you need to know what you've got. The temp sender needs to match the gauge as well, they aren't all the same.

 

[Andrew Mace]

Well, the bulb certainly has to get hot for the gauge to read hot. But even without liquid coolant in the thermostat housing, it would still get hot by either conduction through the metal, or by the steam going by (assuming there was any coolant at all in the engine).

Well, you'd think so, but it's not always the case. Years ago, I had a Saab 99 that would slowly lose coolant (ultimately turned out to be water pump and housing, a true PITA, but I digress....). Yes, to some extent, the temp. gauge would hint at problems. However, the electric fan switch was mounted very high on the radiator. Once the coolant level dropped below that switch, it would not sense the ever hotter coolant, so the fan didn't kick in. Very frustrating!

 

[smaceng]

Many times I have heard reports that the driver said that the temperature gauge reading went up, and the driver was concerned, but did not stop to investigate. then the temp reading went down, and the driver thought all was well. Some time later, the engine blew. Just as was said above, once the water turns from liquid to vapor, the temperature sensor no longer provides an accurate reading (too low) and a false sense of security. If one wanted belt and suspenders (foolish, just watch the gauge), you could add a temperature sensor as used on air cooled engines.
Scott in CA

 

[karls59tr]

In my case I would have expected the temp gauge to read unusually high when unbeknownst to me the bypass hose is pissing coolant all over the ground and the gauge is reading normal giving me no indication that there is a problem. The only thing foolish is to watch a temperature gauge that reads normal when the engine is overheating.