15 replies to this topic

[mbolt998]

I found this excellent thread and calculator, but are the numbers right?

 

https://www.theminif...der-calculator/

 

If we look in the Gentleman's Guide to Smith's Gauges, Table B, it says "Hot" on the gauge should be about 10Ω. But that would be 161˚ according to the calculator. Isn't H normally about 130 or 140?˚

 

https://www.triumphc...es_Pt_1_1v3.pdf

 

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My gauge is reading N at about 70Ω, which I have also tested with some hot water to be about 90˚C. But the calculator puts 70Ω at 111˚C.

 

I've just been looking at my gauge with a variable resistor, and it's putting H at around 30Ω. I suspect it's a bit sensitive on the hot side, which would be confirmed if H is supposed to be 10Ω. But looking at the graph it seems that expecting much accuracy on the hot side is fairly hopeless as in that part of the graph very small changes in resistance correspond to large temperature changes.

[Spider]

This is what I found on test for sender resistance values;-

 

 

The GTR101 and GTR104 values on this table are not the original values, but from those currently available.

I have found that of all those currently available, these are wrong and make the gauge read hotter than is the case. I run the Smiths Universal Sender TT6911-01, with my own fitting adaptors and found them bang on correct.

 

The Smith Gauges fitted to all Minis, from 63-ish to when they went to the Nippons were all Bi-metal types. I've not yet had time to look closely at the Nippon Gauges, but given they work correctly with Smiths Bi-metal Gauge Senders, I'm reasonable sure these too are Bi-metal gauges.

[mbolt998]

Thanks! But very little info there about what to expect above 100˚C (since obviously this is much harder to test).

 

FWIW these are my readings of how different resistances correspond to where the needle is on the dial.I used a rheostat, set it to something, waited for it to settle, took the picture, and then checked what the actual resistance was on the rheostat with a multimeter. The numbers in white are the resistances in Ohms.

 

I wonder if my gauge is a bit sensitive on the hot side, as 17.4Ω is putting it right on H, which according to the Gentleman's Guide, shouldn't happen until we get down to 10Ω

 

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[Spider]

According to the Gentleman's guide, it would actually reach H at 22 ohms. These are a Bi-metal gauge, not semiconductor.

I could have used oil instead of water for the tests I did to get over 100 C, and did consider it at the time, however, the gauges I run are in numbers rather than C - N - H and the hottest I've ever been able to get it to in use was 95.

[mbolt998]

According to the Gentleman's guide, it would actually reach H at 22 ohms. These are a Bi-metal gauge, not semiconductor.

I could have used oil instead of water for the tests I did to get over 100 C, and did consider it at the time, however, the gauges I run are in numbers rather than C - N - H and the hottest I've ever been able to get it to in use was 95.

 

You are right of course. I got it into my head I had what it calls a "TC" gauge. but looking at the back of it now I can see the cork plugs covering the places where you can make calibration adjustments, which matches the illustration in the Gentleman's Guide of a bimetallic gauge. If 22Ω is supposed to be H, then it looks like my gauge is pretty much spot-on and does not need any adjustment.

 

Which means I still don't really know why my car sometimes somewhat randomly goes up to rather near H. I'm not losing any water so I didn't think it was getting that hot But the gauge isn't lying. It seems to be more after hard engine use (and it returns towards N quite quickly idling). Running too weak or spark too late seem like candidates but I think those are set about right. Maybe I should take the carb apart and clean it? This is one thing I never did after recommissioning the car. Cooling system is all new, in good condition, and I've blocked off the bypass.

[Spider]

Which means I still don't really know why my car sometimes somewhat randomly goes up to rather near H.

 

I can't say if this is the cause, but I have had a couple of senders fail on me over the years and these went to a low resistance when in a state of failure. They did 'fluctuate' for a while before finally going sayonara.
 

[mbolt998]

 

Which means I still don't really know why my car sometimes somewhat randomly goes up to rather near H.

 

I can't say if this is the cause, but I have had a couple of senders fail on me over the years and these went to a low resistance when in a state of failure. They did 'fluctuate' for a while before finally going sayonara.
 

 

The sender is only a year old though, and I had the same behaviour with the old one... Wondering if the carb sticking or something might cause it to run lean when you accelerate hard even though it's correct (I think) at idle. Couldn't do any harm to clean it up apart from if I break something.

 

As for the timing, the centrifugal advance is definitely working because I can see it advancing with the strobe. Seems like that would either be stuck or not stuck.

[Spider]

If I can suggest, before looking at causes for it running hot, establish first if what you are reading off is true and accurate. Noted your sender is only a year old, but they can let go at any time.
 

[mbolt998]

If I can suggest, before looking at causes for it running hot, establish first if what you are reading off is true and accurate. Noted your sender is only a year old, but they can let go at any time.
 

 

Well, I do now know that my sender gives me 53Ω at 100°C, and that my gauge reads this at 50Ω:

 

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which looks about right. And that according to the Gentleman's Guide, H is at about 20Ω, which is where it should be.

But what I don't understand is that if it's really getting that hot (it sometimes gets up to nearly H, even in cold weather) I would expect it to boil and lose some water. Also when I have tried pointing an IR thermometer at the head it usually reads about 100°C for "N", but one time when I managed to check it when the gauge was reading close to H, it was only 106°C.

 

But here's something I could try. My multimeter has a 10A range. I could run a wire into the cabin, through the ammeter, and back out to the sender. Then drive around and see what the current is doing when the gauge does go to H. That would tell me whether the gauge is behaving inconsistently. The Gentleman's Guide says they're pretty reliable though. Nothing much to go wrong with a bimetallic strip if it basically works.

 

The voltage regulator is a new semiconductor one from eBay that does seem to give me consistently 9.9V.

[Spider]

The Gauges I have in my Moke are the latest Smiths type, which are a Stepper Motor, however while the gauges are that technology, the Temp Gauge still uses the original type of Bi-metal gauge Sender. This gauge, unlike the earlier Smith Bi-metal gauge is fast acting - instant in fact. When I had a sender go on this car, the gauge would read normal, then after a few hours, flicker rather rapidly between 78 and 95 degrees for a period of a few minutes, then settle back to working normally. I knew from how rapidly the needle was swinging, it just simply wasn't possible for the engine to heat and cool so quick, so I was 99% sure it was an Instrumentation issue. As the hours would wear on (in the same drive) the flickering became more frequent, for longer periods and hitting higher temps. Eventually, I just unpluged it from the sender and when back home, fitted a new one and has behaved ever since.

If this is occurring with a bi-metal gauge, as these are slow acting, you won't see it flickering, but over time will start to read hotter and then likely settle down before eventually repeating this again. This is what I suspect could be occurring in your case. Noted the checks you've done with an IR gun, but if I can suggest, check that on some boiling water to gauge it's accuracy.

Connecting a Multimeter in the way you are thinking may be helpful, but it may also take a little while to understand what you are seeing on it too.

[mbolt998]

The Gauges I have in my Moke are the latest Smiths type, which are a Stepper Motor, however while the gauges are that technology, the Temp Gauge still uses the original type of Bi-metal gauge Sender. This gauge, unlike the earlier Smith Bi-metal gauge is fast acting - instant in fact. When I had a sender go on this car, the gauge would read normal, then after a few hours, flicker rather rapidly between 78 and 95 degrees for a period of a few minutes, then settle back to working normally. I knew from how rapidly the needle was swinging, it just simply wasn't possible for the engine to heat and cool so quick, so I was 99% sure it was an Instrumentation issue. As the hours would wear on (in the same drive) the flickering became more frequent, for longer periods and hitting higher temps. Eventually, I just unpluged it from the sender and when back home, fitted a new one and has behaved ever since.

If this is occurring with a bi-metal gauge, as these are slow acting, you won't see it flickering, but over time will start to read hotter and then likely settle down before eventually repeating this again. This is what I suspect could be occurring in your case. Noted the checks you've done with an IR gun, but if I can suggest, check that on some boiling water to gauge it's accuracy.

Connecting a Multimeter in the way you are thinking may be helpful, but it may also take a little while to understand what you are seeing on it too.

Thanks for the suggestions. I did measure this sender in boiling water before, and got a fairly consistent 53Ω at 100°C. Might test it again though. Also tempted to try to deep-frying it to see what it does at higher temps. After all that is really the range I'm interested in.

[mbolt998]

Well, I tried some tests in hot oil, with my fairly new thermistor (a GTR101 from Minispares, about a year old) and the old one that was in the car since the 90s.

 

It looks like 140˚C corresponds to about 22Ω or so, so I reckon the Gentleman's Guide is confirmed. On gauges that are marked, the "H" mark is usually designated 130˚C or 140˚C, so that seems about right-- I think the water will boil at about 125˚C with a 15psi cap.

 

I also took a few readings from my old thermistor, which seemed to agree pretty much in the important part of the range, but does read a bit "cooler" (more resistance at higher temps).

 

Then ended up slightly damaging the Minispares one by being a clot so put the old one back, which seems to be fine anyway.

 

 

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[Spider]

Good work and now you have some data to work from. It does appear on the face of it to agree with the Gentleman's Guide, but just to throw a wee spanner in that,,,,

As I'm sure you are aware, there is a GTR101 and a GTR104 available for the Mini. The reason for these 2 different senders is for when the factory changed the Thermostats from 82 degree to 88 degree. The different senders corresponded to these Thermostats so that when the Thermostats are at normal operating Temp, the needle would indicate N, which corresponds to either 82 or 88. I think from memory, the advertising blur says something relating to Coopers S's and ordinary Minis which just isn't correct. The change as I recall from 82 to 88 thermostats was related to emissions.

So,,, which the Gentleman's Guide lists resistances at the ends of the scale, I'm guessing these would relate to the sender that suits an 82 degree Thermostat.

[mbolt998]

Good work and now you have some data to work from. It does appear on the face of it to agree with the Gentleman's Guide, but just to throw a wee spanner in that,,,,

As I'm sure you are aware, there is a GTR101 and a GTR104 available for the Mini. The reason for these 2 different senders is for when the factory changed the Thermostats from 82 degree to 88 degree. The different senders corresponded to these Thermostats so that when the Thermostats are at normal operating Temp, the needle would indicate N, which corresponds to either 82 or 88. I think from memory, the advertising blur says something relating to Coopers S's and ordinary Minis which just isn't correct. The change as I recall from 82 to 88 thermostats was related to emissions.

So,,, which the Gentleman's Guide lists resistances at the ends of the scale, I'm guessing these would relate to the sender that suits an 82 degree Thermostat.

Good point, although I don't know if gauges were ever calibrated differently-- too hot is too hot and I guess it doesn't make too much difference whether it's 130˚ or 138˚ when you get up there. It's possible also that the curve for the GTR104 is a different shape, so they kind of match up again at the H end.

 

I'm actually running an 82, but I think my car ought to have an 88 by the book (1979 1000, but with an unleaded head which I fitted circa 1995).

[Spider]

The Gauges were all the same electrically, it was only the sender's that changed.

 

I only just now recalled I have the factory drawing for the gauge, which includes some data about it. C = 52⁰C and H = 120⁰C.