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MG Midget and Sprite Technical - I'm still hot but my Midget is cold

You may recall a recent thread of mine in which I bemoaned my overheating problems. Well I have definitely solved that and the car runs cool - very cool. The temperature never gets above 7.30ish between the C and N. I looked in the archives and the consensus seems to be that this is a bad thing so I'm looking to warm things up a bit (d we all agree?).

The main improvement I made was to have my radiator rebuilt. The radiator guy I use was very critical of my original rad (Serck rubbish) and offered to upgrade it. After the rebuilding the single core of 22 tubes has been replaced by three cores with a total of 63 tubes! The other thing I did was to replace the thermostat with a blanking sleeve. I guess the sensible start is to put the thermostat back - am I right?
Chris Hasluck

Yep. Got to be worth a try anyway.
Good luck.
Greybeard

Replacing the thermostat with a known working one is all you should need to do to get it warming up properly.

The extra cooling capacity will not be a problem if the thermostat works as it should.
JB Anderson

The blanking sleeve is great for a full race engine, although on cold days, I used to tape up part of the radiator to get the engine to run hot enough.

Yes, put the 'stat back in.
Dave O'Neill 2

IIRC there are two thermostats, one for summer and another for winter but can't remember what their values are.
May be worth while running a 'hotter' one if your rad is now so efficient :)
Having just had a shuffty on Moss it seems there are 3 - 74,82 and 88 degress C.
Jeremy Tickle

Put the hot thermostat in. If you don't you will probably need to change it for the winter.

Remember thermostats have nothing to do with cooling. They keep the engine warm at start up and in mine keeps my engine warm enough so the heater works :-) It runs very cold without it.
Dave Squire

The cooling capacity of a cars radiator, fan and water pump should be sufficient for the most stressful situation you are likely to encounter. Possibly up hill on a hot day (30c plus), fully laden, accelerating.
If it is up to that, then at any other time it has too much capacity and needs a thermostat (somewhere) to control the flow of water through the radiator (or the flow of air across the radiator) which regulates the engine temperature (to keep it hot enough to not need a rich mixture, to keep it running efficiently and at a temperature where the oil will evaporate all the bad things that collect in it when running too cold).
Without thermostatic control there is not this temperature regulation and you will likely be running too cool most of the time and only at a reasonable temperature when driving hard, on hot days.
A thermostatically controlled electric fan may be a suitable half way measure, or a thermostatically controlled electric water pump or both or a good old fashioned thermostat and whatever type fan (engine driven or electric or both) you fancy.

Dave
Dave Brown

The saga continues. I fitted an 82 degree thermostat. No effect after a 30 mile run. The temp is still less than half way between C and N. I have no by-pass on the head so the thermostat has about 4 1/8th holes in it to allow for circulation should the stat fail. Do you think those holes could pass sufficient coolant to delay warming?

I'm going to try blacking off part of the grill area next. I suppose too cold is better than too hot!!
Chris Hasluck

Have you checked your gauge?

I did almost cook my engine one day, as I was trying to warm it up before a race. The gauge had developed a fault and was under-reading.
Dave O'Neill 2

Dave
I did think that might be a problem so will check it out. However, it does not get hot enough for the electric fan to kick in so I'm guessing the gauge should be OK.

Chris
Chris Hasluck

I have a 1500 midget, with a new standard radiator, and I replaced the fitted "non calibrated" dual gauge where the water temp is only given as C, N and H, with one which has the temperatures marked on it, although I think the basic gauges are the same.
On mine the temperature pointer always stays well to the left of vertical which on the old gauge would be between the C and N, unless I am stuck in traffic for a while.

JB Anderson

I am not sure whether running cooler is necessarily a bad thing - it may impact economy and performace a lttle as it is essentially removing heat from the engine that could be used to generate kinetic energy - but other than that, and as long as the oil is flowing then so what?

Could be that your rad is now oversized. Blanking off may be an idea or a further fix may be to add a throttling valve in line on the rad intake thereby reducing the effectiveness of the rad and increasing the temp of the coolant.

Thermostat is a red herring - provided the correct thermostat is being used in the first place that is. It should not affect cooling at normal operating temperature. Its function is simply to allow the engine to warm up quicker from cold by restricting or blocking off coolant flow to the block, after which it opens fully and remains open.

Gauges are also indicators only. Check coolant temperature with an accurate thermometer.

Also check mix perhaps. An over-rich mix tends to make the engine run noticeably cooler. Pull the plugs and take a look for soot.

Mark O

Nah cancel the throttle valve - won't work - blanking should though.....
Mark O

Chris,

Most gauges have two pairs of tiny white dots on the outside of the scale. From memory, the lower pair [between C and N] is the calibration point for 50c and the upper pair [between N and H] is the calibration point for 100c.

To test, place the sensing bulb in a tin and add boiling water and the needle should climb to between the upper pairs of dots.

To test the lower point you will require a thermometer to adjust the water to 50c.

My car normally runs around the 7.30 ish position on the scale and I set the Revotec fan to kick in at around the 4.00 ish position.

I recall that Vizard states that most power is delivered at 60c.

HTH
Doug Plumb

Hi Doug
Good tip. I've got two dots between N and H but not the lower one. I'll give that a try.
Chris Hasluck

Chris,

Just found the photo showing the white dots


Doug Plumb

I finally got around to testing my temperature gauge and it does seem to be reading on the low side. At 50 degrees C it has not reached the two left hand dots and falls short of the two dots on the right even when the sensor is held in rapidly boiling water. The 'N' position seems to correspond to about 90 degrees C.

This being so, how is the temp gauge 'calibrated'? Is it a case of twisting the needle to point at the appropriate point or is there some other calibration method?
Chris Hasluck

Obviously this topic invites no interest or comments!

In the absence of any suggestions, here's what I did. After a struggle I removed the bezel and glass and pulled the temp needle off its spindle. Boiled the sensor bulb and put the needle back on pointing between the two dots indicating 100 deg C.secured with a tiny drop of super glue (it was rather loose after being removed). I notice that the gauge does not return to 'C' but I'm working on the principle that getting hot is the most important thing to monitor (correct me if I'm wrong). I'm tempted to buy a new gauge but am shocked at how expensive these are so will see how thing go with the old one before doing that.
Chris Hasluck

Chris, that sounds reasonable.

'C' isn't that important.

The only thing I would worry about is the fact that it has become inaccurate. You have to wonder why, and whether it will remain accurate now that you have reset it.

It might be worth talking to the guy in Redditch that rebuilds Smiths gauges.
Dave O'Neill 2

This thread was discussed between 07/08/2015 and 28/08/2015

MG Midget and Sprite Technical index

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