TR4/4A TR4A Temp Gauge Scale

[RJS]

Hi All

Mine is a 1966 TR4A with a Jaeger water temp gauge. Does anyone know what temperature the readings on the scale equate to? I am pretty sure the center of the gauge corresponds to 185*F (normal). How about 3/4's and (most important) the edge of the "red" zone on the far right?

Thanks

Bob

 

[Sarastro]

I don't think you can generalize, for a number of reasons. One is that the sensors we get today are different from the original ones. In any case, I don't think that 185F is the center of the scale, at least not on mine; mine sits at about 2/3 scale, and I don't think that is much more than 185.

If you really want to know, you could remove the gauge, sensor, battery, voltage stabilizer, and calibrate it in a hot-water bath. Or, just the gauge and sensor and borrow a variable-voltage power supply for it; set it to 10 volts.

But why do you feel the need to know? It would just tell you the water temp at one point in the cooling system--what can you conclude from that? As long as you know where the temp meter needle sits in normal running, attaching a number to it doesn't really tell you much more.

 

[TRopic6]

Hi Bob, FWIW, the TR4 temp gauge has 70 (Cent) at the bottom (168F) and the 4 & 4A used the same transmitter.

 

[Sarastro]

Whattaya know, I remembered that I had done a hot-water cal on my temp gauge. I used a laboratory DC power supply set to 10 volts and calibrated the gauge with two sensors. The first is the one that came on the car; the second is a new, Lucas replacement sensor.

Hope this is legible, but I didn't want to take the time to recopy it; it is a scan of my project notebook. The left column is the temperature and the right is the percentage of full scale, including the cold and hot zones. Ignore the middle column.

This may or may not be valid for your gauge and sensor. No guarantees, but maybe it's still interesting.

I eventually chose the Lucas sensor, as the reading with the first one was into the red zone at reasonable temperatures. But the results with both were similar.

 

[RJS]

Thanks Gents,

Steve, your notes are helpful. I am less concerned on what my gauge actually reads. What I am really trying to determine is what temperature Standard-Triumph considered "hot" - i.e. in the red? I have no proof but, it seems Std-Triumph calibrated the "edge of red" at ~205*F, with full red representing ~212*F (the boiling point of water). Please let me know if you agree/ disagree...

From my understanding, water temp is really not a concern, so long as the engine doesn't boil over. Having said that, I am running 50/50 water/coolant with a 7lb cap. That puts boiling at/about 230*-240*F. Suffice to say, if the engine and cooling system are in good nick, I should never see those kinds of water temps under street use. However, I suspect many Triumph owners become needlessly concerned when their temp needle moves off the middle to the right - believing the engine is overly "hot". However, I think the point of the gauge is not to indicate the engine is running hot but, rather, your coolant is getting closer to potentially boiling over - which is the real concern. But, up til the point of boil over, all is OK.

Last, I've done some less scientific measurements but, when my temp gauge is exactly in the middle, using an infrared temp gun I measure 185*F at the radiator tank inlet.

On a slightly related topic, I'd be interested to get some data on oil temps...

Regards

Bob

 

[Sarastro]

Yes, I think that's all is correct and makes sense.

From my notes, you can see that the edge of the red zone was 196 deg with the "original" sensor (i.e., the one that came with the car) and 205 with the new Lucas sensor, which I'm now using. The latter makes sense to me. My engine runs around the 2/3-3/4 point in ordinary use.

 

[TR Tom]

It always really bugged me that a maker of serious sports cars would go from a really useful mechanical gauge with lots of numbers, in the TR3, to one with just one (centigrade) number, and then none at all. To make matters worse they fed it with an unreliable electrical sensor. This was the functional equivalent of the temperature gauge found on Ford Falcons of the era.

After a multi day trip in 100+ degree temperatures where I had no idea what was going on under the hood I finally took action. In addition to performing every cooling system upgrade possible (another subject for another thread) I went and bought a Stewart Warner mechanical gauge, which fit perfectly in the old hole. I now know exactly what’s happening temp wise, even with the key off. The black and white dial and font fits in with the other originals, although I did also replace the oil gauge just to balance things out. One of the gauge restorer’s said he could even put original TR style bezels on them, but now that I’m used to the look, I’ll probably never get around to it.

Anyway, that’s my solution. My TR4 will never win a concourse award, but I’ve always been more of a function over form guy.

Tom