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MG Midget and Sprite Technical - could one gauge do two things?

i have been debating which gauges to install and which ones i do not need, and so far i have not found a gauge i do not want so then it comes down to practicability of money, space, and sensors which gave me this idea:

The smiths water temp gauge is a variable resistor which changes resistance proportional to heat, so therefor no matter where the gauge is installed it will give a heat reading albeit not scientific accurate, good enough to know when you are about to overheat. Which makes me think if I were to weld a bung into my oil pan and fit a water temperature sender I could hook that up to a temp gauge and get a reading, then comes my idea; why a separate gauge? install a single pole double throw (SPDT) switch which will allow me to switch between which sensor to read, which in reality is just switching between which resistor to use for a path to ground.

does anyone see any problems in this idea?
Stefan

^^^ the smiths water temp sensor is a variable resistor which changes resistance proportional to heat, so therefor no matter where the sensor is installed
Stefan

nothing wrong with the theory at all Stefan. One of my earliest memories is of my father's 1949 Rover 10 which had a fuel gauge with a button next to it. Press the button and it turned itself into an oil level gauge.
David Smith(davidDOTsmithATstonesDOTcom

You could use one of the smiths combined oil pressure/water temperature gauges, and just plumb it in to the sump or the pipe to the oil cooler.

Cheers Carl
C Bintcliffe

Stefan, does your midget have a padded USA dashboard?
I have the same problem with that dash.
I already changed the center console to ad a voltmeter, twinmaster, extra light switches and readinglamp.
Now i have no place to put new gauges but i still want a oil tempeture clock.
I already have a combined water temp./oilpressure gauge.

My plan is to remove the heater-switch-cable at the most left of the dashboard(is same size as small Smiths gauge) and put the oiltemp.gauge in.
As i never used it(always on defrost)this switch im not going to mis it and it can always be put back.
I does need a little cutting but that cant be seen when either the switch or a clock is in place.

i couldnt find a picture of my dash with the heatercable-switch on it but its to the left just out of sight o this picture




Arie de Best

After re reading your thread i realized my anwser isnt really what you asked but i thought the idea behind your question was to combine 2 funtions in one gauge/clock because of lack of space for seperate clocks.
Arie de Best

As long as the two temperature sensors were identical and had a sufficently linear range for the temps covered by both oil and water, say 60-120 DegC then its perfectly possible to have a dual functioning gauge.
Nick

Yes - Russ Morgan uses one for water and oil temp on his KMidget.

You need (apart from 2nd idential sensor, obviously!) a 2 pole changeover switch to determine which sensor is connected to the gauge at any one time; oh and remember which position for water and vice-versa.

Don't forget oil can go to 130/140C.

(I use a second water capillary gauge for oil temp, and the fact it maxes at 110 isn't really a problem, except on track days I can get the needle all the way to the end stop!)

A
Anthony

Yes nothing wrong with the concept. Normal instrumentation in industry uses a platinum resistor for sensing and this is 100 ohms at 0 degs rising by 38.5 ohms per hundred degrees upto about 600 degrees and above so no difficulty with ranging. (wonder if the resistance bulbs on a car are the same resistor? never checked!)
The only week point I can see is the switch, any high resistive contact here would cause big inaccuracies, in idustry we would use a switch with gold contacts for this kind of application.
Bob (robert) Midget Turbo

Arie,

You mean like I did on my 78?
http://www.spritespot.com/gallery/albums/Stefans-1978-Midget/Midget_interior_October_2002.jpg

I have a right hand drive dash which is metal and am not cutting it up, so I have decided to fit the fuel and temp gauges in teh dash and then in the consoul do some welding patch work and turn it into a control center housing electronics such as megasquirt and maybe a relocated sterio reciever.

Stefan
Stefan

Exactly Stefan, thats what im planning to do to!
And here i was plesaed with my idea and then finding out somebody else already "invented the wheel". :)

You can never have enough gauges and switches(read toys) in your car just like these Etype jaguars have.
Becaues when i grow up i want to be a 007. LOL
Arie de Best

The water temp gauge for the late 1500s was electric, but I thought all the gauges for the A series engines were mechanical, can't double up the senders for those. In theory what you propose would work with a mechanical gauge, but without calibration I don't see that the information would be all that useful. The water temp gauge should have the range needed for the oil which usually should run between about 170 to 230 degrees F. The padded dash does present a problem for those of us that want additional instruments. I made up a new dash just to find a place to mount an oil temp gauge.
Bill Young

Bill,

I removed the mechanical sender from the head of the 1275cc and fit the electric gauge and sender from a 1500cc car.

http://www.spritespot.com/gallery/albums/Stefans74RWAMidget/midget_07.sized.jpg

http://www.spritespot.com/gallery/albums/Stefans-1978-Midget/P1020190.jpg

I have the electric senders on both of my 1275cc cars, when i converted the 1500cc 78 to an a series engine i just pulled the sender off the 1500 and bolted it onto the 1275cc and everything worked fine. That rules out the posibility of a dual gauge running an electric sender though.

I remember when I pulled the mechanical gauge off the 74 the adaptor to the block was corroded to the sender and after destroying the mechanical sender and adaptor to the head I ended up just screwing the sender into the head with out the adaptor.

does anyone else run an electric sender and gauge on their 1275?
Stefan

This thread was discussed between 07/02/2008 and 08/02/2008

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