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MG MGA - How hot is hot?

The archives are full of ideas on how to reduce the engine temperature. But what is the ideal temperature we should be aiming at?
At times I have been envious of cars that never get near exceeding 190 degrees but then on the other hand, aren't engines supposed to be hot to run efficiently. After all the standard thermostat only opens at 82 d C which is about 180 F so that should be the very minimum it should operate at?
Not saying it wouldn't be nice to drive and check out the views rather than focus on the temperature gauge all the time, but what is the general thinking?
Graham V

Ideally the hotter the better from an efficiency point of view.

If your rad cap is pressurising the system correctly then you can safely use an 88 degree C (190 F) thermostat.

The temp guage is misleading - generally anywhere under the H or 212 degrees is OK and nothing to worry about if it is steady at that.
Chris at Octarine Services

Read this:
Then stop worrying and enjoy the drive.

Ideal coolant temperature is something between 180dF minimum, and pretty much anything less than boiling. When it gets around 220dF or higher you can start worrying about boiling fuel in the carburetors.


My thinking Graham is, if the gauge starts moving early enough, and there is no indication of boiling, it's fine. Our gauges are not that accurate in allowing tight judgement of temps.
Allan Reeling

That picture of Barneys is both impressive and scary, I have never seen a temperature gauge needle that has climbed up into the oil pressure dial before!

I too tend to get a bit concerned when the temperature gauge gets up around 212 F level, the main thing to remember is that the pressurised coolant in the MGA doesn't actually boil until it gets to around the 230 degree mark.
So, as long as your coolant isn't boiling, then your cooling system will still be actually working.

The important point is that your gauge should show some temperature variation, for example, it will climb when you are stood in traffic or when climbing a steep hill (particularly on a hot day) But the temperature should correspondingly fall when you are driving along again or when you drive down the other side of the hill.

If the temperature just keeps on climbing and shows no sign of dropping, then there is something wrong.

Colyn Firth

Yes that photo is pretty scary, especially bearing in mind that Barney is busy taking a photo at 90mph !
When the temperature rises in traffic, my other concern is that of fuel vaporisation. I have a bilge pump which I think helps, though never really tested it scientifically.
I was once stuck on a hot day in a long queue of very slow traffic leading into Henley, and experimented by releasing the bonnet catch - thinking that there may not be enough exit points under the bonnet for the hot air to find its way out. It didn't seem to make much difference, but who knows, maybe it would have got even worse had I not done it.
I have also toyed with the idea of installing an additional heat shield on the other side of the spacers. Or sourcing a more efficient heat shield. That would be an easy fix if it worked.
Graham V

Lol - yes I have seen a temp gauge reading 80psi!

Actually popping the front of the bonnet doesn't help - it allows cooling air over the top of the rad rather than go through it.

Best idea is to remove the rubber sealing strip at the BACK of the bonnet - just leave two bits in the corners to steady the bonnet on its hinges - the area in front of the screen is a high pressure area and cold air will flow into and help cool the engine bay.

The area under the front wings is a low pressure area so it you want extra hot air vents then the inner wings are a good place to put them.
Chris at Octarine Services

This post got me into deep thought after reading Chris's and Barney's posts. All interesting points. I have always been an advocate of getting all the basics right as a starting point, the main one being the original cored radiator. That's what they designed in the factory and that's what's worked well for me. I rarely see my temp above 190 in the UK temperate climate. In fact I can watch my thermostat opening and closing on the gauge. Always makes an interesting read.

Then I thought about my additional set-up and whether it has any influence on the running temperature. I am talking about the MGB expansion tank system on my motor. I have my expansion tank on the forward face of the firewall with an engine length pressure hose to the radiator overflow pipe. The pressure cap is on the expansion tank and a blanking cap on the radiator. The radiator is always full to the brim and with water in the connecting pipe to a reservoir of about a pint in the expansion tank. My total heatable water capacity therefore is about a 12% increase over the standard. So does this help the cooling?

On the warm up cycle heated water is initially pushed along the pipe to the expansion tank due to water expansion. After that the water becomes more or less stationary in the pipe but heating of it and water in the expansion tank continues with conduction. Does this alter the indicated temperature on the gauge? Overall I think not. But it does have an effect. I think it slightly dampens the rate of temperature increase on heat up and temperature loss on shut down. In other words it very slightly dampens out the peaks and troughs in rates of temperature change but does not alter the overall indicated stabilised running temperature.

Steve Gyles

I don't know whether your car has read the Drivers Handbook, I guess mine has because it usually conforms to the following ...


The temperature of the cooling water leaving the cylinder head is indicated by this gauge and should be approximately 160 to 190'F. when the engine is running normally. If the normal running temperature is greatly exceeded the cause must be traced and rectified immediately."

Mind you, the Handbook doesn't say what temperature "greatly exceeded" might be, so I'll go along with Barney's comments.
J N Gibson

It should be easy enough to make a double layer heat shield for the pushrods engine, each fitted either side of the insulators: it'll add a couple of gaskets.

I would make them independent of each other also, with the air gap between them helping the situation hopefully.

I am in the throes of making a heat shield for the distributor of my Twin Cam (distributor and electronic ignition close to the exhaust heat on a Twin Cam). I bought some small, lightweight, dimpled aluminium sheet from B&Q for about £8, its easy to cut and fabricate. 2 sheets would do it.

I think the current offerings achieve very little and you could transfer the insulating 'pads' from the existing shield to the lower one of your installation.

Colin Manley

Yes I think I will do that at some stage before the weather warms up.
As well as the second shield, do you think sticking some of the "sticky" heat shield material to the existing shield instead of the original fabric material would make much of a difference?
Graham V

I was experimenting with various heat shields of increasing complexity for a couple of years, back when. Still have one on my car. They can help a little when the car is moving some. But when you have to stop and stand still, and you're operating the Dutch oven under the bonnet, the heat shields don't work for squat. Quite easy to install the little 3-inch bilge blower, and the hot carburetor problems go away. It is the only reasonable fix I know for having to live with modern gasohol fuel.

These inner fender louvers do help remove air from the engine compartment.

Gene Gillam

I was in Spain with my friend in his MGA in 2016 -ambient temp around 25C - on a long climb up a steep hillside road the temp gauge went off the scale into the oil pressure half - it was like this for about 5 minutes until we got to the top (no places to stop safely). Opening the bonnet , expecting a cloud of steam - there was nothing to see - just a hot engine - after a short stop for a breather and a check of water level ( non needed) we were on our way again.
Cam Cunningham

Water boils 212dF (100dC) at sea level.
Pressure adds 3.25dF (1.8dC) for each 1-psi.
7-psi on water = 235df (113dC).
50/50 glycol/water coolant ads 20dF (11dC)
7psi +50/50 = 255dF (124dC).

My temperature gauge is set to read 212dF when the sensor is immersed in boiling water (good as it gets). It runs out of mechanical travel at 82-psi, and it does not boil (with 7-psi and 50/50). If I switch off at that point, and let it heat soak, it still doesn't boil. As long as there is liquid coolant in there, and it is not boiling, the engine will be okay.

It's the carburetors that suffer from boiling fuel at such elevated temperatures. Around 220dF on the gauge, and standing still or creeping in hot weather, it will begin to stumble. 10% gasohol fuel can boil at about 165dF (if it is not flowing). You can pull the choke out to keep it running. The cure for this is the little bilge blower in the air duct in front of the air cleaners.

Why on earth would you want to run at 212deg
If it was a methanol burner, yes I understand the need for that but an MGA on petrol---I'm a 170deg thermostat fan (76 c)
Stay cool man
William Revit

I like heat from the heater in cold weather. I have a 180dF thermostat, so it runs 185dF minimum in cold weather, and higher in warm weather. 190dF is quite cool for warm weather running.

If you run it much cooler like 160dF for instance, the fuel doesn't vaporize as well, so it has to run overly rich, and the excess fuel washes oil off the cylinder walls (and dilutes oil in the sump).

Fellow MG A owners, On running HOT__
I commence this note, with the following recognition.
Guru Barney Gaylord , is a wonderfull contributer engineering and long term experience wise to both this and the Nth. American Cite.
His contributions are well researched, engineering-wise. Reliable. I have never meet Barney.
Inexperienced MG owners can well take the advioce in his articles with confidence.
He gracefully, published my article on his Barney's Cite under CO 209--
in relation to my fix of these cars on-going cooling difficuilties.
He gracefully published my "FIX", without comment†, as to its value---
You should read CO 209.
The radiator of my 1800 cc Coupe has never crossed 80*c in 25,000 miles of running--in our sub tropical high temperatures-- & with Air Cond., in use. Check the item -- the air intake mod shown on CO 209.
Recently, the car's petrol consumption over 259 miles with a MegaSquirt EFI system was 7 gallons of fuel.
I hope your MG is as ecanomical as this--with fantastic road performance to match. And don't suggest the EFI, completely.
The faulsehood suggestion that driving these English cars with a coolent temps of 200*F + is O.K.---- That is just stupid. Bad engineering.
Well read this---
I am looking for an un cracked Cylinder head, to fit out with 1.625 valves to go with my EFIed 1800cc ebgine. I have checked 8 cylinder heads so far---All cracked and unserviceable. I wonder why?
How could this be? A design fault? How many Ford or G.M. Heads get to be unserviceable in this fashion? Those engines Never--run at those temps, unless there is a sudden issue. And then even, the heads usuially survive.
BMC heads were a weakness back in 1956. Lots have cracked and become unserviceable, in the mean time. There has to be a good reason for this.
You be the judge--read CO 209 Think about the physics --
Its not rocket Science---deciede what you should do to save your cylinder head..
I.W. Cowen.

I am obviously the owner of the magical mystery car, but I am in agreement with the guys from down under.

Over three different engines in thirty years of ownership, (each engine exchanged for more power) I have always had issues with running too cool, and for years have a radiator blind fitted so that I can close off the airflow to the radiator from the driver's seat on a cold-running day. If I leave the blind open on a cold day (5C or so) my engine doesn't get above 50C. I have a 82C thermostat fitted and my gauge also calibrates at 100C in boiling water. Closing the blind brings the temperature up, and then it can be partially opened to regulate the cooling. If the gauge has ever climbed into the oil pressure it was as a result of a coolant system failure somewhere.

On a hot day (38C ambient) even running up mountains 80C is the max I see on the gauge until I stop. But on a hot day in traffic, heat soak to the carbs is a problem, which is why I am about to fit a bilge blower too (I just need to figure out where to put the switch). I don't think we have methanol in our fuel here.

The radiator is a standard issue original type core.

MGAs were not known for overheating when new, so they should still work the same today. I suspect many will benefit from the following process:

1) richen your mixture a little
2) retard your timing a little
3) overheating problems will vanish
Dominic Clancy

I had similar experiences to Dominic although not quite so cool once I calibrated the sensor as described by Barney. I have always been an advocate of the original core radiator. I never go over 190 when running. I can see the thermostat opening and closing all the time.

I never found any benefit from the bilge fan when stationary. I worked many hours on it and was never convinced its output was pointed at the carbs. I even put deflector vanes on it. I eventually put it in the other ducting to give a boost to cockpit airflow. I have recently got the best results in slow traffic with the asymmetric 7-blade fan.

Standard road use MGAs in the UK do not overheat if correctly set up and with the original radiator. If yours does you have got it wrong somewhere. Electric fans and oil coolers are just sticking plasters. The cause is beneath the skin.

Steve Gyles

I know you are not all members of the MGCC but if you are and have read the series of articles on the Manchester University lab experiments you will know that a lot has changed. Today's petrol is a very very different chemical mix to the product of the 50s and 60s and these changes are very relevant. It is a lot more than just the additional of ethanol. We are now dealing with a different issue. Personally the only problem I have really have is vapour lock and that didn't happen in the old days, and the above articles tell you why.

By the way I do remember boiling the A in the early 70s, but this was probably due to the general 'banger' state of car then and leaking hoses.

Paul Dean

I donít want to start an interstate war but Iím in Barneyís camp. 10,000 kms run through Europe and UK in summer (4 days over 37C) no problem with MGAs overheating. My cars, roadster and coupe, normally have no problems with overheating in Oz even in +35 C days. Yes it has happened in peak hour stop start traffic in the city where it gets up to 220F but i can manage that, pull over or slip up a side street. I donít reckon MGAs need any major modifications to handle todayís temperatures, just make sure your cooling system is in good condition and drive according to conditions.
Mike Ellsmore

Have a look at my earlier post on operating temperature this year

Mike Ellsmore

My car is a 1958 Fixed Head Coupe 1500 and have fitted louvres to the bonnet...
Two rows 4inches wide and 4 inches apart, 20 louvres per row which gives a over all length of 20inches...
I estimate the under bonnet temperature has reduced 10degrees......Rex Thompson
Rex Thompson

A photo please Rex?
Barry Gannon

This thread was discussed between 11/02/2018 and 25/02/2018

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