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MG MGA - Electric Fan

I fitted an electric fan to my 1900 motor to overcome a very high running temp during our hot summers. It works well but I'm thinking I might be able to remove the mechanical fan to get an improvement in horsepower, and to make a difference to the economy.
That is my task for today, a cool 25 degrees here in Melbourne.
In high temperatures, and with both fans running, it runs cool enough on the open road, but in stop-start traffic it gets a bit hot.
I will report results after we have a 40 degree day (which may be after Christmas).

Seasons Greetings to all, Barry

BM Gannon

Barry I have recently removed the engine [yellow] fan from my 1500c A. So far the electric fan is coping well. Set to come on at approx. 200% and cuts out at 190%, running a 7lb. rad. cap I'm not concerned about boiling. Probably at around 225%. A 185% thermostat and a good radiator keeps the temp fairly stable in
the 185 /195 range. The highest temp. I've seen so far is about 205%. Left idling for 3 or four minutes on a fairly warm day the fan brings the temp back down ok. On a 175 mile run last week end with some very steep climbs the car returned 36mpg, Brim to brim in the tank ,98 octane. [the trip is accurate] I'm also running a 3.9 diff. Sean
S Sherry

Sean, I wish I could get close to your mpg. I am currently only getting about 22mpg. So I need to lean it off a bit more. My 3.5tonne motorhome gets 32mpg!

I have just had a small radiator leak fixed on warranty, so I suppose they gave it a good flush, yet again. I'm also running a 7lb. cap and have set the electric fan to kick in at 185c. I will report after the festive season on the success, or otherwise, of removing the mechanical fan.
BM Gannon

Hi Barry,

We installed a set of twin fans on a Supercharged MGA with an 1800 overbored about .030, ported pretty well and still develops 8.5psi with a large passenger and about 8.0 with just the driver. This is the extra boost pulley. Anyways, the twin electric fans cool well in slow traffic, so the owner tells me.

If you look carefully, you'll see that the frame is built to install in the car after the coolant system is installed with a bolt on the top and bottom to split it. We didn't want to poke holes in the radiator or drill additional holes in the bodywork and these fans were a little larger anyways so his frame system really did well for installation off site, no issues and can be completely removed if we decided it was not what we wanted.

Also, the car still runs the stock steel blades with a Moss fan shroud. Let me tell you that the Moss shroud with the Supercharger is a bear to adjust the belt!! Anyways, you can substitute the MGA/early B metal blades for a Light Weight Plastic fan blade from the early 1970s MGBs. They work well and weigh far less and have a little flex too. You can have your cake and eat it too.

I like the idea of electric only but frankly hearing an MGA with an electric fan and gear reduction starter takes away from that sacred stubborn way. -says the guy with a Camaro V6 in his MGB.

BMC Brian McCullough

Fortunately, as Barry knows, I do not suffer from overheating (just the opposite in fact) so I have not considered messing around with the original fan arrangement.

But also, like Barry, I am amazed at the 36mpg claim. Sean, how did you get that mileage worked out on on a 175 mile run?. According to your figures you would have barely got the tank down to the half full level? If your guage is anything like mine it goes down slowly to half full, then drops like a stone. One tank full of fuel and one journey has so much guestimation(?) in it that I would disregard it. I have been doing an accurate spreadsheet for the last 18 months and the overall figure has settled down at 23.25mpg. However, this has included individual tank loads of a high of 30.51 and a low of 15.94 (small fuel leak). Lots of drivers make extravagent claims without doing any meaningful research.

Steve Gyles


I can get over 30mpg repeatedly, I don't have a spreadsheet but instead keep the petrol receipts and compare to the mileage, starting and finishing with a full tank.

If I drive hard I can figure around 25-28 and if I take it really easy around 32-36. I think I could reach 40 if I took it even steadier, but that's not what the car is for! I drive probably over 90% on unrestricted A roads. I don't have any figures for short journeys or urban (stop start) driving as I hardly ever do any. I run the car slightly lean (or slightly advanced, i.e. slight pinking on hard low rev acceleration) with nice light grey exhaust and light coffee coloured plugs.

I have an 1800 3 main with std carbs, mild tune cam, std gearbox and 3.9 rear axle.

Next year I will keep a spreadsheet so I can share accurate and audited figures!
Neil McGurk


My car spec is very similar, 5-bearing, 5-speed, 3.9, correct colour plugs etc - 23mpg. Where does it all go? My commute journies are 8.5 miles each way each day. I guess that accounts for some of it, but surely not the additional 10mpg average.

I still think a lot of people kid themselves about how good their mpg is. I went down to London and back the other week in the Merc, 260 miles each way. The car computer said I was getting 36mpg, but when I punched the refuel figures into my spreadsheet from both ends of the journey I had actually acheived 30.83 and 30.81 respectively. Overall, it is only getting 28.73 and that is a very latest edition C-Class with AMG upgrade.


PS. Maybe my spreadsheet is rubbish. Template on my website.
Steve Gyles


I'm not an MPG optimist, my Focus 1.6 struggles to get over 30 mpg and I don't "feel" that I drive it as hard as the MGA (but my journey times always seem less!!)

My MK2 Jag is down around 10mpg but it's quite highly tuned and stinks of fuel!

My car transporter does about 27mpg and is very consistant because it only really goes at one speed (50-60)!

The wifes MGB Auto seems to be doing around 20MPG but hasn't covered so many miles yet.

Maybe you have US gallons or Swedish miles!

Neil McGurk


I will admit to a sporty right foot. Not many cars go past me during my commutes. In fact, a couple of days ago my work colleague followed me to a seminar. When we arrived he said how nippy my car was and at times he struggled to keep station in his VW GTI. Nice compliment really for a 50 year old car! And absolutely nothing to do with Barry's electric fan thread. Sorry Barry, got carried away.

Steve Gyles

Steve, Lets keep it going, someone may eventually tell us how to achieve a higher mpg!!
BM Gannon

Steve, the run I did was all on relatively traffic free roads, one third freeways, early Sunday morning on a cool day. The tank took slightly less than 5 gallons of 98 octane. The car is std. 1500 in very good condition. I run a new electronic distributor [Moss Mts.] 14% static, total mech. advance 34%, plus vac. adv. of approx 8% [on cruise] Carbs have rich needles
[CC ?] to help keep the combustion temp. under control. Long branch ex. manifold helps the breathing. A 3.9 diff keeps the revs down. I drive in the 3000--3500 rpm range. [My tacho is approx 200rpm optimistic.] My understanding is that an electric fan consumes about 5HP. I also understand that the B series engines run best in the 200% temp range and 34% timing to give the optimum pressure thrust at around 20% after top dead centre on the fireing stroke. Also I run a 185% thermoatat with a blanking sleeve. The higher running temp gives greater gas expansion on combustion. This is how I see things Steve, I'm sure others see it differently.
Beauty is in the eye of the beholder. Sean down under
S Sherry

Steve, further pearls of wisdom ! As an engine looses
one H.P. for every two degrees rise in ambent temp. I endevored to keep as much hot air as possible from the carbs. by blocking the rising hot air from the ex. manifold getting to ihe carbs. Together with feeding as much cool outside air to them via a four inch hose from in front of the radiater. I also blocked the space under the hot air outlet forcing as much hot air as possible out from under the bonnet
S Sherry

Barry, I will accept your challenge and take a shot at explaining the route to better fuel economy (and I hope people can tolerate a longer message).

The last 50 years of automotive engineering has not increased engine internal thermal efficiency as much as you might think, so our older cars do have a shot at coming close to newer cars. A hotter running engine should have slightly more efficient fuel combustion, but it can also waste more energy with heat escaping out the tailpipe and through the cooling radiator. Higher compression should improve thermal efficiency, but modern engines are not much higher compression than our stock MG engines.

For least fuel consumption the fuel mixture needs to run very close to stoichiometry most of the time, except for brief periods of acceleration or throttle shut down. An exhaust O2 sensor and dash gauge may help to determine the best needles for the SU carbs to get as close as possible to this target. Running rich will waste raw fuel out the exhaust. Running out of tune in any direction can screw up combustion can cause the engine to run hotter, which in turn wastes energy through the exhaust and cooling system. So the first priority with any engine is a good tune up.

If you want good fuel efficiency, stick with the stock cam shaft. A high performance cam can produce more power, but the increased valve timing overlap will in most cases result in more unburned fuel going out the tail pipe during more mild driving conditions (light throttle cruise). Porting the head and increasing valve lift without changing cam timing may yield more power with full throttle while retaining original fuel economy at normal cruise.

Once the engine is optimally tuned you can go after pumping loss and thermal efficiency from the outside. Reducing engine speed (and increasing torque) at cruise speed helps a LOT. First reason is that the slower running engine reduces pumping loss. That is the amount of hot gas (energy) going out the tail pipe and the amount of fuel necessary to produce that much heat energy. Think seriously about changing final drive ratio from 4.3 to 3.9 as the first easy and relatively cheap step. This 10% reduction of engine speed for cruising may result in about 5% reduction of fuel consumption. Part of that is reduction of pumping loss, and part is from improved thermal efficiency. The later detail is to follow immediately. These cars can benefit from a much greater reduction of engine speed, like an overdrive gearbox or 5-speed giving top gear ratio at least down to 0.78 and possibly as low as 0.67.

Considering that it takes a fixed amount of engine output energy to move the car down the road as a given speed, the slower running engine will be operating at higher torque in cruise mode. The closer you get the engine to operation near the torque curve on the slower side of the torque curve peak, the better will be the thermal efficiency (more power relative to less waste heat). You may notice the peak of the torque curve for the stock MG engine is around 3500 rpm, so the first target might be to fix the overall final drive ratio to avoid running the engine any faster than 3500 rpm at your fastest normal (or most common) highway cruising speed. If you commonly cruise on open expressways at 75 mph, then you need about 0.80 overdrive top gear to go with 4.3 rear axle ratio. If you install the 3.9 axle ratio, then you still need minimally 0.90 overdrive or 5th gear ratio. But that's just the starting point or minimum change in the right direction.

All MGs in stock form will run at cruise speed with substantially less than full throttle. Give it a lower final drive ratio and/or overdrive or 5-speed gearbox, and the same is still true, maintaining normal cruise speed with less than full throttle, even into a head wind up going up a mild grade. As you change more toward overdrive gearing the engine speed can be to the left of the peak of the torque curve with increasing torque output, and the operating point will be getting closer to the curve (but still under the torque curve). This will be improving thermal efficiency at same time as reducing pumping loss. The point of failure in this progression is when you run into a head wind or a mild up grade, and the torque requirement rises to a point above the torque curve (at full throttle), and you have to downshift to keep from slowing down.

To allow for this last issue you want to avoid over gearing that would reduce engine speed too much, so you can still run into a head wind or pull a mild grade without down shifting. This break point depends entirely on the torque curve for your engine (and of course the load it will be pulling). An engine with larger displacement, larger valves, better porting, or a supercharger will have more torque available and can pull through a lower final drive ratio. If you get the final gearing right a supercharged engine could have slightly better thermal efficiency while running slower at cruise speed, again depending on how close you get to the torque curve. An engine with less torque can't do that and would need a numerically higher final drive ratio (less overdrive). If you install a radical performance camshaft that moves the torque curve to the right, it may have more peak power buy will not pull highway speed with the same lower (lowest) final drive ratio.

Getting to the bottom line, and approaching the original question, you may be surprised to hear that a bone stock weak in the knees MGA 1500 can likely pull a 0.70 overdrive gear into a mild head wind at 70 mph, and get substantially improved fuel economy in the process. More powerful engines could handle even more overdrive with good results. Just keep in mind that when you want to pass someone briskly or drive up a steep hill you still have lower gears in the gearbox available to immediately negate that long overdrive gearing.

As to what fuel "best" economy you might expect, in 1988 we had half a dozen MGA in a caravan, all with slightly different configuration, 4 engine sizes, 3 final drive ratios, all 4-cylinder 4-speed. We were cruising hundreds of miles in a caravan at steady speed of 59 mph (due to 55 mph national speed limit and a few out of tune wheels that would jiggle at 60+). They were all getting between 31-33 mpg with no overdrive.

In 1997 I drove my MGA 1500 with 4-speed and 4.3 final drive up and down the Haul Road (Dalton Highway) in Alaska. We were traveling mostly at a steady 45 mph on a rough gravel road with some significant hills in places. For a few days and more than 1000 miles the car was getting 30 mpg with these less than optimal road conditions. The only trick there was slow cruise and much reduced load from wind resistance.

A friend of mine drives a 1275cc MG midget with 3.9 final drive and a 5-speed gearbox. I don't know the exact overdrive ratio, but I think it is a Datsun B210 gearbox. He is a very conservative driver tending not to exceed the speed limits. I personally witnessed this car getting 42-45 mpg with open road cruising. My best estimate for MGA or MGB is, if you can run an "aggressive" overdrive ratio and keep cruise speed down to something reasonable, these cars may be able to make close to 40 mpg (US gallons), which would be higher number with imperial gallons. I might like to try it someday, just once for the experience, but I imagine it might be somewhat boring driving like that long enough to save enough fuel to pay for the 5-speed gearbox. Meanwhile I'm satisfied with regularly getting 25-28 mpg at expressway speed with the trailer in tow, 3.9 final drive and no overdrive.
Barney Gaylord

WOW! Barney, I will take that 'book' away with me for my holiday reading. You have certainly given me food for thought. We are heading out into the country for the holiday break and my one regret is not being able to drive the motorhome and the MGA.
Thanks again for the info. Barry
BM Gannon

I assume I can divide Barneys MPG figures by 0.832 for UK gallons. i.e MGA caravan 37-40 and himself satisfied with 30+

Steve, Barry, time for a tune up?!

Steve is your commute stop start or motorway? Stop start and a heavy right foot would explain it.
Neil McGurk


Sporty right foot, not heavy, there is a difference. I very much feather the throttle, not floor it.

2 lanes each way for most of the way, 4 roundabouts, 6 traffic lights, 2 speed cameras, legal limit of 50 mph (tends to get ignored in the open country part of the road - most of my journey).

My 23mpg from cold, morning and evening, is what I expect on these commutes. I am not disappointed. I know that the car will do a bit over 30 mpg on a long boring run down the M6. I use the car every day on these short journies, come rain, snow and sun shine, and on this basis, 23mpg is totally reasonable. Many people who claim the high mpgs I suggest base their figures on the odd Sunday leisurely drive out for a picnic and are wrong if they think this is an average consumption; a one off tank load consumption for a specific type of journey maybe, but not an average consumption that is of any value, covering long and short journies.

Steve Gyles

Coming back to Connecticut from GT-33 in Pennsylvania, mostly on secondary roads with very limited expressways, my 1600 was getting 39 mpg. I was traveling with two friends, one with a ZA Magnelle and Marv Staurt with his 1600. Both MGAs have 3.9 rear ends, Marv has an OEM four speed and I have one of Hi-Gearís five speed in mine. He was getting 36 mpg to my 39 mpg and those were figures that his wife calculated for both cars. Thatís on a US gallon, but burning hi-test fuel. I did not work out a spreadsheet for it but I feel that the car runs cooler and you get better gas mileage with (93 octane) hi-test.
David werblow

This thread was discussed between 14/12/2008 and 19/12/2008

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