Always check your Temp gauge calibration

[Tdafforn]

Hi All,
I have been getting to know my new Stag now that the weather is kinder.
This has meant driving it around in a range of traffic in the warmer weather.
One of the things I am always really keen on in my old cars is that they do not have any overheating tendencies. Just for the record, my car is a RV8 conversion.
Anyhow the car generally sits at 90oC when driving below 60 mph. It cools nicely on the fan (new electric fan and recored rad) when idling at standstill. But the temps sometimes rise to 100 and perhaps a little more at higher speeds and after spirited driving where I am reving hard in lower gears. The temp drops back down when I return to normal driving but I still don't really like it..
Anyhow I decided to check the calibration of the gauge using an Infrared Thermometer measuring the temp of the manifold where the sender is.. Interesting results.. bascially the guage is reading 10-12 degrees high.. which means cruising temp is 78 which makes sense as I have an 82 degree thermostat and hacking the car is more like 88 oC..
Good news!
Guessing the issue may be either:
1) mismatch between the sender (which is new) and the guage
2) Tired gauge
3) Tired Voltage regulator

Have ordered a solid state regulator.. if that doesn't work, guess some resistors in the circuit would work. could do trial and error but does anyone have a recipe?
Tim

[sujitroy]

I did some experiments with some spare temp. gauges and spare voltage stabilizers. I was able to find a Triumph dealer document on how to check these. Swapping out the stabilizers and using the same gauge resulted in different temperature readings.
As mentioned may times before, just get used to what you have and use the readings as a base line. I drive my auto with the gauge at times just below H on the gauge. Any higher than that It's time to stop. It's been like that for the last 20 years or so.

Sujit

[Wheelz]

The surface temperatures are lower than the coolant temperatures, so you can't calibrate your gauge that way.

Senders and gauges vary in their performance but any error is often down mainly to the sender. LD Part do a sender which might give a more realistic reading.

[Tdafforn]

The surface temperatures are lower than the coolant temperatures, so you can't calibrate your gauge that way.

Senders and gauges vary in their performance but any error is often down mainly to the sender. LD Part do a sender which might give a more realistic reading.

Have put one on order will be hood to compare.. suspect the temp read from the surface isnt 12 degrees different but will be good to see
tim

[MikeParker]

The surface temperatures are lower than the coolant temperatures, so you can't calibrate your gauge that way.

Senders and gauges vary in their performance but any error is often down mainly to the sender. LD Part do a sender which might give a more realistic reading.

Chris,
That may be true if you are measuring off the block, but off the thermostat housing, which is alloy, should be pretty good. Just make sure to paint it because metal reflects IR so you end up measuring what the metal is reflecting if you are not careful..

[Goldstar]

The surface temperatures are lower than the coolant temperatures, so you can't calibrate your gauge that way.

Senders and gauges vary in their performance but any error is often down mainly to the sender. LD Part do a sender which might give a more realistic reading.

Where does your electronic gauge take its temp feed from Chris? Is it possible to integrate it with an old fashioned temp sender that only gives out an electrical signal or is there another fix? Top hose maybe?

[flying farmer]

Chris,
That may be true if you are measuring off the block, but off the thermostat housing, which is alloy, should be pretty good. Just make sure to paint it because metal reflects IR so you end up measuring what the metal is reflecting if you are not careful..

I have noticed that frequently, totally different readings between the matt black of the hot side of the radiator and the aluminium parts of the engine

[dasadrew]

Sorry if I'm raining on anyone's parade here and, to be frank, after a bottle of Primitivo I shouldn't be typing anyway, but....

this whole temperature shebang is driving me nuts. After several months down the rabbit hole, with IR thermometers and the like, and measuring Xfr housing temperatures where the reading jumps dramatically if the beam touches the Xfr housing or one of its bolts, and, in any case, it's not the water temperature which you're measuring. The difference between LH & RH Xfr housings is significant, so why should the LH housing be the reference point? Can anyone show me documented evidence what the temperature in the LH Xfr housing should be? I doubt it, as the aim of Triumph in 1974 was probably just to ensure that nothing was "in the red" on the dashboard for a new owner.

There are too many pseudo scientists who are trying to derive formulae for herding cats. The old SOC article(s) on the subject point us in the right direction of what to do to reduce an overheating calamity, and those empirical recommendations are, in my opinion, the only way to go. Not sure if I'm being too dramatic, but just observe the behaviour of your own Stag. If it's not spewing out water due to dramativ boiling, forget whether the gauge is showing 88°C or 91°C. If you're concerned, by all means try out the "secret spoiler", the fan cowling, an electric fan, a new viscous coupling, a Supergill radiator, or whatever else is out there; but forget about trying to get the gauge to show 2°C less. The Stag was a mess at the outset, and it wasn't just pure bad luck of the draw which made it fail internationally. Until someone proves that a 91°C reading on the gauge will mean piston meltdown in the next 500 miles, I think we're perpetuating the Stag paranoia with this particular temperature OCD.

Oh well, the Primitivo bottle is now empty, but let's get our "concern train" back on the rails for the really serious issues like stub axle breakages, rear hub failures and the like.

Cheers

Drew

[wilf]

As I mentioned on the now closed thread, overheating has never been a major concern on my engine, (it has other foibles) and its cooling system behaves exactly as I would expect and have seen on several other (mainly yank) dinosaur V8s with similar systems. Including RV8s.

I have run some measurements using thermocouples glued to the theromstat outlet, and rad in/outlets which showed entirely "normal" behaviour, with approx 20C drop across the radiator at anything over 20mph, and the thermostat outlet temperature fluctating slightly as the 'stat opened and closed as you would expect. (yes, mine does actually close at times!)


Much worry seems to stem from the fact that the temp sensor, as standard (and as on mine, in fact, even with a mechanical gauage) senses from THE hottest spot on the whole engine, as noted by others above. It is not representative, other than in a relative sense, of the overall coolant system temperatures. The heat soak after switch-off is, IMHO, entirely normal.

[Wheelz]

Chris,
That may be true if you are measuring off the block, but off the thermostat housing, which is alloy, should be pretty good. Just make sure to paint it because metal reflects IR so you end up measuring what the metal is reflecting if you are not careful..

I was not necessarily referring to measurements taken with an IR gauge. I have tried various methods of bolting sensors to the metal of the head, and I found that coolant temperatures were always a few degrees higher. An IR gauge would have its own uncertainties as has often been discussed and noted.

[Tdafforn]

Sorry if I'm raining on anyone's parade here and, to be frank, after a bottle of Primitivo I shouldn't be typing anyway, but....

this whole temperature shebang is driving me nuts. After several months down the rabbit hole, with IR thermometers and the like, and measuring Xfr housing temperatures where the reading jumps dramatically if the beam touches the Xfr housing or one of its bolts, and, in any case, it's not the water temperature which you're measuring. The difference between LH & RH Xfr housings is significant, so why should the LH housing be the reference point? Can anyone show me documented evidence what the temperature in the LH Xfr housing should be? I doubt it, as the aim of Triumph in 1974 was probably just to ensure that nothing was "in the red" on the dashboard for a new owner.

There are too many pseudo scientists who are trying to derive formulae for herding cats. The old SOC article(s) on the subject point us in the right direction of what to do to reduce an overheating calamity, and those empirical recommendations are, in my opinion, the only way to go. Not sure if I'm being too dramatic, but just observe the behaviour of your own Stag. If it's not spewing out water due to dramativ boiling, forget whether the gauge is showing 88°C or 91°C. If you're concerned, by all means try out the "secret spoiler", the fan cowling, an electric fan, a new viscous coupling, a Supergill radiator, or whatever else is out there; but forget about trying to get the gauge to show 2°C less. The Stag was a mess at the outset, and it wasn't just pure bad luck of the draw which made it fail internationally. Until someone proves that a 91°C reading on the gauge will mean piston meltdown in the next 500 miles, I think we're perpetuating the Stag paranoia with this particular temperature OCD.

Oh well, the Primitivo bottle is now empty, but let's get our "concern train" back on the rails for the really serious issues like stub axle breakages, rear hub failures and the like.

Cheers

Drew

completely get many of the things you say. I have had a fair number of old cars and there is always a period of understanding its natural rhythms. Things like oil pressure and engine temp, transmission noise and warm up choke procedure. In these procedures it can be important to have some orthogonal methods to make measurements like IR thermometers. In the end a temp guage that reads under can lead to a warped head which is pretty disasterous. It is true that limitations of IR temp systems need to be understood. But when methods are limited and you understand the issues they are very helpful. Heavily used in professional motor racing. In the end you are correct the key thing is that the system does not have any boiling particularly in the head and that the owner understands the signs a particular car gives when things are going well
tim

[trunt]

It’s always amazed me how people expect accuracy from a gauge that relies on a “stabiliser” which basically is a heated bi-metallic strip and a gauge that is also a heated bi-metallic strip!

For me, It points where it points… until it doesn’t then you do something.

[jbuckl]

Fwiw, if an accurate thermocouple was calibrated & fitted to the top hose, & was showing 90 degrees c, that would be ok when the engine was fully warmed up.
However, seeing as the cars gauge is only an indicator… without numbers or graduations, how could they be aligned or correlated?
maybe an infrared thermometer could be calibrated to a thermocouple though…. Wouldn’t need a triumph though

[dasadrew]

Actually, they do have calibration marks on the scale which relate to certain voltages. When I was down the rabbit hole I actually did check the calibration on the gauges I had, and the voltage stabiliser is electronic and indeed gives out the required voltage.

[Dieter H. Marschall]

Drew, funnily enough we both have the same taste as to cars - and wine! My favourite Primitivo at the moment is "Doppio Passo" ...
Best wishes,
Dieter.