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MG Midget and Sprite Technical - Testing temperature gauge

I wanted to test my 1275 coolant gauge, as the engine seems to run too cool. I put the sender into a kettle and brought it a good old boil, the gauge only indicated jut past the normal mark.
I thought this confirmed my suspicion but on reflection I thought the system is normally pressurised, so the boiling point will be higher, so perhaps the gauge is OK.
Anyone know what the normal running temperature is. ( my gauge is the cold normal hot type).

Dave
Dave Barrow

The gauge should read 100C or 212F with the end in boiling water. It's true the boiling temperature that rises under pressure, but 100C is 100C whether under pressure or not.

You can recalibrate the gauge by removing the needle carefully, putting the bulb in the boiling water and eating a minute or so before refitting the needle so it points to 100C or 212F depending on your scale.

Some dual gauges have a small lever behind the dial face to re-calibrate as well. but you have to remove the face to get at them, so may as well try the quick approach first.
dominic clancy

from the chart at the very bottom of this page
http://study.com/academy/lesson/how-to-calculate-boiling-point.html
it looks like boiling point with a 15 psi cap will be close to 250 F.
It can be calculated with Gay-Lussac's Law if you want to check it.
David Smith

Is the time you eat critical Dominic? :)
Jeremy Tickle

Thanks all, but as I said originally my gauge only reads Cold, Normal, or Hot, so without knowing the exact temperature of normal, I still cant calibrate it. Can someone with a gauge that reads actual degrees tell me what there gauge reads at normal temperature. Thanks.

Dave
Dave Barrow

Smiths temperature gauges should have a pair of 100 degree calibration dots which when testing with boiling water the needle should be somewhere between. (arrowed in attached image) there are another pair calibration marks too, which if I recall correctly are for 60 degreesC

Jim


J Smith

Just to add, on my 1275 midget, with normal driving, the gauge needle lies just to the left of the straight down 6 o'clock position. When I turn the engine off it normally rises up to about the 5 o'clock position for a while before dropping back to the left.

Jim
J Smith

Here's a pic of a farenheit gauge from Paul hunt's 'site. You can see two dots either side of 140° and the lower of the other two dots just below 212°.

As Jim said, between the two dots should be 100°C.


Dave O'Neill 2

Thanks Jim and Dave, I will have another look at it, great help.

One reason I think it has been running too cold, is that I get a touch of mayonase in the oil filler cap on short runs, but this burns off on longer runs. I am pretty sure the head gasket is OK.

Dave
Dave Barrow

mine is a 1500, but my (aftermarket) gauge reads about 80 degrees C during normal driving. agrees with Daves picture, 180 deg F is approx 82 deg C. so you could calibrate normal to that if you wanted.

Malcolm
Malcolm Le Chevalier

Here is my Cold Normal Hot gauge with the calibration points highlighted. My car normally runs around the 7 o clock position.


Doug Plumb

Re the boiling temperature of coolant ... as well as the pressure, it depends on your antifreeze concentration-

https://in.answers.yahoo.com/question/index?qid=20100529050826AAm9T9O
Geoff_MG TF

This thread was discussed between 05/02/2016 and 07/02/2016

MG Midget and Sprite Technical index

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