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MG Midget and Sprite Technical - Water temp – what, where(?)

I’ve always struggled with the idea of the readings on the water temp gauge on the 1275 crossflow rad cars at least.

Looking at things in a gauge general type of way, ignoring the slight variances of correctly calibrated gauges and the interpretation between the C-N-H and numbered Centigrade gauges and variances of exact opening and closing of different makes of thermostats, the numbers don’t add up/match.

For my car which has had two gauges during my ownership (so far) that registered the same readings there seems to be a difference in interpretation and details of thermostat and water temp readings.

I don’t have access to infra-red thermometers or other such equipment I just have my car’s gauge, new nine years ago, and my wonky eyes, faulty for nearly six decades.

I have an 82C thermostat that I can clearly tell when it (fully) opens by the movement of the gauge needle, with the new rad it’s like a big dump of cold water on the transmitter bulb.

The gauge’s transmitter bulb is in the cylinder head just before thermostat housing.

The calibration dots on the gauge I think are at around 50C (60C?) and 100C.

Take the photo of the numbered Centigrade gauge below as an illustration of numbers not shown on the C-N-H gauge.

Let’s say for argument’s sake that the thermostat is fully open at 82C so shouldn’t the needle on the gauge be around the ‘N’ (82C) range when it fully opens, or settles, as the temp transmitter bulb is so close by? – on my gauge it’s shows as thermostat (fully) open at around the (65-ishC) area of the gauge well before ‘N’.

So if the car is supposed to normally run at around ‘N’ (82C) on the gauge is ‘N’ actually at ‘N’ on the gauge or should ‘N’ be at around the (60C) area of the gauge well before the present position of ‘N’ on the gauge?


(most 1275 X-flow Spridgets I’ve heard of normally run well before the ’N’ on the gauge)



Nigel Atkins

If you "know" for a certainty, when the thermostat opens and are sure that it is correctly responding at 82 degs C, why don't you adjust the needle on the gauge to point at 82, instead of 65?

Alternatively you could remove the bulb end from the cyl head and put it in a beaker of water, maintained at boiling point, and check that the needle does in fact point at 100 C

If anything, with the bulb positioned in the head you might expect it to be very slightly hotter there than in the thermostat housing.
GuyW

I can't know for certain that the needle drop, or even that the stat is fully open, at 82c but I can clearly see that it's well before the 'N' and was on the same on the previous gauge, the drop just seems more noticeable with the new rad (standard) fitted.

I don't really want to remove the gauge and fiddle about with it as disturbing items that are working often seems to led to problems either with them or other items around it.

Testing the bulb might not be so bad as I've still got some red sealant that I could use if the bulb to head adapter starts a weep leak as it did when I first fitted this gauge (I can't remember what I used then but it worked).

I'd too guess that the bulb position might be hotter than the thermostat housing which would mean the needle position on the gauge would be slightly even more retarded than it actually shows.
Nigel Atkins

I meant to put I that I was previously lent an infra-red thermometer to check reading as various points but its readings were unreliable when tested on the car and elsewhere so I considered the thermometer to be faulty.
Nigel Atkins

The problem with an IR thermometer is you need to know the emissivity of the surface or you will get an inaccurate reading.

http://en.wikipedia.org/wiki/Emissivity
David Billington

It always appears to me that the temp gauges are a bit slow to respond to temp changes. I suspect there is a lag time in the operation of the guage itself.

So is it that at the moment the thermostat opens - which you can tell by holding the top hose and feeling for that sudden change in temp - the gauge is still showing the temperature from some moments earlier? Or does it just never catch up?
GuyW

I would expect that it should indicate approx the thermostat opening temperature. System starts with thermostat closed, engine heats water until it opens and lets hot water through. The radiator (+ fan assist) should always be capable of cooling a hotter engine down, so when enough cold water comes back the thermostat starts to close and thus reaches a steady state, give or take the reaction time of the waxstat.

I don't know what mine does - the capiliary for the original gauge broke, then it had a temporary electrical CNH and an oil light as a replacement but at some stage the temporary gauge vanished.

<thread steal alert> Did any car have a version of the dual guage with an electrically operated temperature sender?
AdrianR

Thanks, David, although I'd no idea what it's called I had allowed for emissivity and I always test the testing equipment before carrying out every test having once wasted hours trying to track something with a faulty tester.

A trick I'd suggest to be used to test youngsters who'd been on technical courses was to remove the fuse from the plug of the equipment that needed repairing because they'd be thinking of showing off all the technical stuff they'd learnt when many call-outs (or preventable call-outs) were for very mundane reasons and just needed the "bleeding obvious" checking.

With the infra-red thermometer I was greatly helped by being told it *might* be suspect before being lent it.

My cheap multi-meter is the same, as it's infrequently used it sometimes plays up I usually test it by applying it to the midget's battery posts to see what readings it gives as when I once used it on the Midget's fully charged battery it started with a reading of about something like 9.6v and increased its reading by about 0.1v every second yet the next time I used it it was fine. I only now use it as a gauge (estimate) or yes/no tester.
Nigel Atkins

Fitted a 72 c thermostat in a B during the week and the needle sat on the 170 line on a gauge like your lh one in the pic
At startup cold it went a bit further ,probably up to 180 , it was almost straight up and down then swung back to around 160
It did this a couple of times while warming up then settled on a steady 170

If you've got a glass thermometer, lay it on the top hose with the bulb close to the thermostat housing and tape the bulb onto the hose so the air can't get to the bulb
It will read fairly accurate
William Revit

Guy,
I don't know as I can't remember, I'm almost sure at sometime I done the feel the top hose test for the stat to open but can't remember where the needle was on the gauge.

I'm not sure you're right about the time delay as the needle on the two gauges I've had seem very mobile and active at times but perhaps they are registering historical events.
Nigel Atkins

Adrian,
not that I'm aware of, all dual gauges had the water temp via the capillarity(?) tube and bulb. The later 1500 with single water temp gauge was with electric sender. With the electric gauges and senders the trick is to match the two up.
Nigel Atkins

Hi Willy,
did you mean you fitted a 74c stat or can you get 72c? I'd like to try an 85c stat, I've tried a 88c but normally use the 82c - all for all year round use.

Unfortunately I don't have a glass thermometer, the room temp wall thermometer is wooden cased and only goes to 50c/122f.
Nigel Atkins

The way id approach this is very easy simple fast and cheap

Get a high quality kitchen cooking thermometer like $ 5.00 the wife may have one in the kitchen draw

Get rid of the wife for an hour

Put a small pan of water on the stove with the kitchen thermo in the water plus your thermostate and the bulb of the temp gauge in the water...all three

Heat the water up and watch it keep an eye on the kitchen thermo for the temp reading ... does it match e automotive gauge reading ...watch the stat to open and when it does what is the temp on the kitchen thermo vs what is on the auto gauge

If the auto state is supposed to open at 82, and the auto gauge is saying its 82 and the kitchen thermometor says 82....

Your golden if one is off you will know which by the kitchen thermometer comparison

Tip take percautions that the 3 pieces are not making direct contact with the pan as that could make for a false reading


Simple, easy, and fast....(cheap?), that depends on how the wife spent the hour when you kicked her out the door...haba

Prop
1 Paper

Good idea Prop but not for me as we don't have a cooking thermometer and I don't want to take the gauge out of the car.
Nigel Atkins

Nigel
Yep 72c
It had an 82 but the guy lives up in the hills and it was getting a bit warm on the long bendy uphill sections so we're trying a 72 -so far all is well
The car has my favourite hate an electric fan
instead of the normal belt drive
willy
William Revit

The thermostat does not govern the temperature that the engine will run at. All it does is help the engine to warm up quicker by shutting off the radiator until the calibrated temp is reached. From then on the 'stat should be wide open all the time.

Putting in a lower temp 'stat won't make the engine run cooler. All it will do is put the radiator in circuit earlier, so the engine will take longer to reach optimum temp, and the heater will take longer to become warm. The final running temperature of the engine is governed only by the efficiency of the radiator, fan and water pump, plus how clean and clear the water passageways are.

If Willy's engine is really running at 72C, it is running too cool which can be as bad for the engine as running too hot. Ideally you want the system to hold around 90C during normal operation. That's hot enough to boil off condensation in the engine and get the oil working properly. The MGF has an oil temp gauge and the handbook tells you not to rev the engine above 3000 rpm until it reaches 90C.

The water temperature gauges on our MGs are the source of endless discussion because they actually show what is happening inside the cooling system. Of course it goes up when the car is stuck in traffic. Of course it goes down when the ambient temp is low. That's why a modern car has it's gauge controlled by the car's electronics to sit permanently at the central zone, not registering all the fluctuations that occur. If a modern car gauge shows a high temp, something is definitely wrong. That's not the case with "our" cars.
Mike Howlett

That's the thing Mike if the engine is best run at 90C then why is the 'N' at the 82C position and not the 90C or is this to allow for 8C difference in the position of the bulb transmitter.

Or is it that the temp at the bulb position is the same for the rest of the engine (within reason) so the 'N' position is a bit low.

Same with oil temp does it vary (within reason) depending on where the transmitter is positioned.

Hence my what, where in thread tittle.

I've read for Minis that for maximum power 70C–75C (160-170F) is wanted but this would be too low for the oil in a road car so 85-90C is better.

During the winter with a 82C stat my gauge reads around 60C or less (140F) yet the heater when used is still hot so I'd guess the back top of the engine at least must be at least warm.

Whilst the engine temp isn't governed by the water stat surely it will make a difference at what temp it opens and closes with heat retention/residual, to me it seems the quicker and longer the heat is allowed to build the longer it takes to dissipate.
Nigel Atkins

Nigel

To modify my idea to still work and not remove the gauge is still simple

Same as i posted above but just take the pan of water to the car remove the bulb and heat the water with a small propane torch/ oxy acetylene torch or an electric hot plate or similar

Cookimg thernometors are cheap and common i got mine from aldies for about $5.00 so about 3£ in your money its a temp gauge with a sharp metal stick attached to the bottom ... mainly used for testing the temp of ovan meat like turkey, corned beef roast as well as pastry cakes and testing boiling water temp
1 Paper

Prop,
I don't do shopping and don't like the thought of one-use items and we're already clutter enough at home, there's not as much space here as in USA.

Anyway I've kinda sorted it and will report my findings when I've one finger typed them.

When I pointed out to my wife the loss of heat from taking the pre-heated (tea of course) mug of boiling water from the kettle in the kitchen on its about 30 foot (9m) path to the car she suggested taking the electric kettle outside as within 4 feet (1.2m) of the car is a fixed external electric socket - doh!
Nigel Atkins

Just to add (because I can) emissivity has a massive effect on the measured temperature, and needs careful consideration as David says. Among other things it depends on the colour and texture of the surface being measured. It's likely that an infra-red thermometer is calibrated off a 'black body' type emitter, and the more expensive the detector, the more likely this is; therefore should give a close-ish result if measuring black things.

I used an extremely expensive and sensitive IR camera to create this http://ieeexplore.ieee.org/document/4717654/
Rob Armstrong

Nigel - Mike
You are living in a dream world if you think the thermostat doesn't control the engine temperature-------That's what it's there for' to keep the engine temperature at the desired constant temp

Try running without a thermostat and you will see that at standstill and very low speeds the temp will come up but as soon as road speed is increased and air starts flowing through the radiator, coolant temperature will drop dramatically
With a thermostat it stops the temp dropping off at speed and saves your headgasket etc from all the expansion/contraction associated with temp changes

Also - there was a mention of oil temp--
Although coolant temp will effect oil temp a little they are not that directly related
Changing a coolant thermostat by 10deg doesn't change oil temp by 10 deg--It may change a little but not directly related

willy

I still hate electric fans
William Revit

Willy, what's the problem with electric fans ?
GuyW

Willy,
thanks for pointing out my error, I thought "wot's 'e on about" until I reread my post.

I meant and should have put -" Whilst the engine temp isn't *fully* governed by the water stat" - with the rest of the sentence to suggest the stat's importance. Sometimes I miss out the word 'not' in a sentence which can have a similar effect, as has been proven many times my typing isn't the best.

I know the importance of the water stat but made a poor job of promoting it in that post but have done better in previous threads and posts.

One of the purposes of this thread was to see if I should retry using an 88C stat again, last time I didn't get along with it but others have, I'd have preferred to try an 85C stat if one was available.

I know there are problems with electric fans but I much prefer them to the engine driven fan and fitted an electric fan and removed the engine fan eight years ago. It's controlled by a stat (well thermoswitch) and doesn't have an override switch so I'm fully committed to stats. :)
Nigel Atkins

All good--

Guy
My little issue with electric fans is a personal choice/hate thing
A properly set up electric fan system is ok but most aftermarket kits leave a bit to be desired
The way I see it is a normal belt driven fan keeps the coolant coming out of the radiator cool enough so that it can cool the engine when demanded by the thermostat operation
A good electric fan would have the fan ticking over all the time and have the fan speed increase when needed--Most late model factory electric systems are like this and I havn't got a problem with them
But the on-off style aftermarket systems that rely on top hose water temp have the problem of for example, when you get stuck in the traffic with no airflow through the radiator the whole cooling system heats up until the fan clicks in ,then the fan has to cool the whole lot down again--It's no big deal but really I'd just rather have a normal fan
I did set one of my V8s up once with an electric fan with the temp sensor in the bottom hose set at50c and that worked
reasonably well, at least as soon as you pulled up in traffic the fan came on instantly which with a V8 is needed to stop the whole system generating too much heat
The best setup I've had on a V8 conversion was a viscous fan driven straight off the front of the crank pulley
willy
every to their own i guess, it's a good pub subject--plenty of opinions
William Revit

Willy,
I don't disagree with most of what you've put and totally agree each to their own. I'm thinking most would reply that an override switch on the electric fan would cover one of your concerns. Personally I think an override switch is having a dog and barking yourself. I'm with you about the electric fan not preventing heat build up but I dislike the engine driven fan, a two stage setting on the electric would be good.

A mate had a Dolomite with a viscous fan and boy was it loud but so is my electric fan another mate always comments on it when we pull up at junctions.

The top or bottom hose subject was discussed fairly recently, one I might have started or at least contributed to.

I've seen a photo Mike put up on the MGB side that he might put up here, leave that to Mike.
Nigel Atkins

This thread was discussed between 02/09/2017 and 05/09/2017

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