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MG MGB GT V8 Factory Originals Technical - MGBGT-V8 Cooling

I have a 1974 MGBGT-V8. I find that in the hot summer days that if I come to a stop in city traffic that the twin factory fans cannot cope. The rad, water pump is new and I am running the coolest thermostat. This is not a new problem, I have had this issue for years. I am running a stock factory set-up engine, carbs, exhaust etc.
I wish to install a third fan on the engine side to overcome the problem. I am concerned about clearance between the rad and the water pump. Any recommendation as to a water pump with a shorter nose and/or a Electric fan that would fit in this application ?
I have done some local investigation into buick water pumps from the 1961 Buick Special that would fit and have a short 'nose' but, what about the pulley etc ? Any suggestions ?
Thanks !
Jordan Jones


Have you tried "Water Wetter"? I have a few friends with big Healeys who solved theiroverheating problems with this product when all else had failed.



The stock yellow fans are not efficient - this can be improved with cowling, or changing to fans with cowling. I would also recommend water wetter check out Redline web site. Recoring the rad will also help or changing to an Ally Rad.


I have had the same problem with mt 1974 GT V8.
I have replaced the thermostat twice, flushed the (new uprated)rad 2 or 3 times with no improvement.
I have the same original set up as you, 2 electrics fans, 1 has been wired to be operated manualy from the dash board and I had to swich it on the instant I stopped in the traffic.
What seems to do it was to swich to semi-synthetic oil, the change in the way the engine run is quite incredible. It is so much smother, quieter and generaly better running but more importantly it has completely cured the over-heating problem.
the temperature gauge now hardly creeps pass the mid way point even in the traffic.
It could be coincidence but that's the only thing that I've changed and the problem was cured overnight from that moment.
I hope it will be of some help,



I'm about to try synthetic oil, so will keep on watch on temp during summer.


I should also mention that I use a short nosed w/pump but there would still not be enough room to squeeze a large fan in the space. In general it may worth considering to small say 6ins pullers just above anti roll bar. Also filling the gap between front valence and rad is supposed to improve cooling. In addition an exhaust manifold coating (not exhaust wrap) will help keep temperatures down.


Had this problem with my V8, i was only getting about 10-11 volts at the fans and a loss of available amps too,due to dirty connections ,dirty relay contacts and bad fuse box connections etc.I dissmantled the fans fitted new brushes, greased the bearings and cleaned all the contacts/wiring and the problem was cured.
It is also a good idea to fit two relays, one for each fan and a supply to the relays straight from the battery side of the starter motor(fused of course),this gives a good strong supply of juice,with minimal volt drop and a high fan speed. :)



can you tell us which kind of oil ( brand and viscosity) you use in your GT V 8?


My factory V8 struggles in summer. I have seen the needle in the red while stuck in traffic in ambients of 90+F. Didn't boil although it was starting to get very rough. I had the idle higher than normal to keep the oil pressure up, which added to the heat problem. After a couple of rad leaks I fitted a 25% uprated unit of identical dimensions and it was noticeably better. However the fans still cannot maintain 'N' stuck in traffic in high 70s/low 80s, even with the heater on too.

I also am interested in Claude's semi-synthetic brand and viscosity (fancy not telling us what it is!), have you seen the 'Oil Viscosity' thread on this BB?
Paul Hunt

In the height of Summer/traffic etc the temperature should stabilize well short of the red section (although it will increase above normal) using the stock fans. If you have a problem the usual items to look for are: Oil (more below), fuel/air mixture, distance of fan blades from rad (should be very close indeed), the rad itself (they have a short life), water/antifreeze proportions (the best antifreeze also has water-wetter), radiator expansion tank cap efficiency, gas leaks from the engine, thermostat bleed hole, number plate position which in the UK stops air flow.

You shouldn't need another fan although many of the sucker fans are more efficient -- if you have got room behind the rad.

The second relay may increase reliability - it shouldnt do much for fan efficiency.

Finally the point about oil - we forget that oil is the primary coolant and that the buick/rover V8 has a tendency to sludge up. Good quality oils with high detergent properties will clean them up but the best deal is to change oil every 3 or 4 K Miles - and once your engine is reasonably clean - use the cheapest 20/50 (10/40 with later engines or in Europe during Winter) rated at least SG.

In summary - no additives - no extra fans - change oil frequently. But I can't speak for engines putting out more than 190 BHP.




The second relay is to lower the current across the contacts, so you effectivly have two fan circuits.The two fans draw alot (for the size and ratnag of the realy)of amps at start up, causing arcing and burning of the relay contacts(over time)thus giving rise to volt drop and a loss of efficiency..
A manual overide switch is also a good idea while you've got your tools out(ooeerr).My warmed over factory V8 only ever got hot when there was a problem with the fan relay or when the brushes were so worn that only one was working, other than that it aways stayed in the middle of the guage even in summer traffic..:)

That should read:size and rating not ratnag, sorry..hic!
John UK

Claude Kent

I can't remember exactly what actual brand of oil I used, all I remember is that it was one of the leading manufacturer (Shell?Total?Elf? or maybe something else) but it was a well known brand.
The viscosity was 10/40w.
I doubt if the actual brand makes a lot of difference.
All I did was to follow the advice of the engineer at "Discovery Engineering" Maidstone, ex RoverCraft. They are well known for knowledge of performance engines & Rover V8 in particular.
The guy's reasonning was that I would probably be OK with general "cooking" oil for plodding around if I changed it every 3000 miles but would do the engine a favour by running it on a better quality oil, mostly if I did push it a bit, which I do occasionally with the odd week-end blast on the continent, and if I was to take it for more stressful work, ie. track days or such I should go for fully synthetic oil.
The added advantage of using a better oil is that the milage can be increased to 6/10000 miles between changes therefore I don't need to change it twice in the summer.
It goes without saying that I change the filter at the same time.
The difference on the running of the engine is such that I have started to run my diesel van on semi-synth. oil, (diesel oil naturaly).

But the other query that I have is regarding the front brakes.
I know the BBS is full of tips but I'm still as confused as when I first got started.
The original set up is probably adequate but, by modern standard, not more than that and I have been toying with the idea of fitting 4 pots SDi callipers.
My query is: are they really involved to fit and more to the point are they worth the trouble?
I hope it will have helped,

J. Claude cazzola

Claude, in re the front brakes: I personally don't think the 4-pots conversions I have seen tend to be much of an improvement. My roadster V8 conversion has a set of Princess 4-pots and my GTV8 conversion has bone stock MGB 1800 brakes, albeit with x-drilled rotors and s/s hoses. Neither car has a servo, and both are dual-loop setups mostly scavenged from US chrome cars. I can't tell a bit of difference stopping-wise and in fact the GT's pedal is definitely firmer. Boy does it stop well. The pain and suffering I endured in fitting the Princess setup was unbelievable ... and was apparently in furtherance of nought ... I later saw a drawing comparing the swept area and it is hardly any better with the Princess setup. Maybe there are other setups (like real GTV8 brakes) that are better but one only has so many free quid and hours on this earth. The Princess setup was, as I recall, noticeably heavier as well.

Regarding brakes. I have found the V8 rotor and Triumph 2500 caliper setup very simple to do and while not improving the stopping all that much, can stand a bit more heating up on the race track. The std setup works very well but you should consider pad material before anything else. On standard pads, braking from 125mph to 30mph is not out of the question in 80 metres! It is the number of times per minute that you do this, that require uprated pad material. Also, look at your tyres. There is only so much rubber on the road and your car is light.
Ross Hannah

Hi Jordan,
I saw a nice small fan that fits on a stock pump last summer. You can get them from Andy Achauer at
He's just south of you in Ohio.


As Roger pointed out above these engines tend to sludge up and the only way to remove this is by regular oil changes, whatever oil is being used.
The use of synthetic should improve mpg making it cost effective compared to regular branded oils.

The Wilwood 4 pot alloy brakes are light and easy fit, pricy at 450(available from Cambridge Motorsport). It may be possible to reduce this cost by importing Wilwood calipers and using a peugeot vented disc. The additional pots increase pad stability rather than radically increasing swept area and vented discs improve cooling.


Hi all.
Get yourself an uprated rad from the likes of Malcolm Beer (Houghton near Huntingdon Cambs) you will amazed at the difference....I run standard thermostat, standard cooling fans (original), have 217BHP at the wheels and get stuck in the Finchley road at rush hour often during the summer and it never gets to more than three quarters on the gauge. The fans come on quite a lot (no surprise there) but it will never boil over all other things being equal. The only things you may consider is a manual switch for the fans so you can switch them on a bit earlier and make sure the whole engine is free from muck, the carbs are spot on and the timing is also right. I know other racers that have this rad and getting the thing hot enough is more of a problem than keeping it from boiling....The rad isn't that much more than a new standard one (well if Malcolm takes a shine to you that is...) and onlt takes minor work to get it to fit (bend down/chop out a bit from the front shelf as it is a bit thicker...

Re front brakes. Have an early Range Rover set up on mine which work pretty well. Not sure how this compares with standard as I have always had this set up on the car.

S H Pickford

Oil: Just refilled with GTX Magnatec (synthetic). Again care is needed selecting the right one, there are two - one for basic engines and one for modern but the packaging is almost identical. Gauge seems to be rising faster than with the Duckhams but the temps are above freezing again at the moment so not strictly a fair comparison, cold pouring is faster though. The Duckhams had only been in for 400 miles but was already showing brown on the dipstick. With the regular oil and filter changes I use Forte and it is amazing how adding clear Forte to hot slightly brown oil turns it dense black after 15 mins or so fast idling.
Paul Hunt

Hi Jordan,
If you don't mind cutting the front tray and moving the rad forward a bit, you could fit a bigger puller fan that would go a long way to solving your problem. I didn't want to do the cutting, so I fitted 2 eight inch pullers and a 12 inch pusher without any other mods. This combined with bonnet louvres and an improved front tray to the rad, works extremely well. The factory water pump set-up and the Buick 300 water pump line up with the crank pulley the same.



COOL MGB V8 in 90 degree summer traffic: make sure timing is correct, make sure air/fuel mixture is correct, short Buick water pump, 12" flex fan(unless MGC hood is used then 14" flex fan will fit, must space the 14" fan away from pulley belt though, and YES it will be close to radiator), MGB GT V8 radiator, 160 degree thermostat OR 160 degree collar restrictor(only recomended in summer), MGB dual electric fans, oil cooler with Suzuki GSXR-600 motorcycle fan mounted on oil cooler(small and inconspicous), fan should come on as dual electric fans switch on. Correct antifreeze mixture with water wetter product. This should keep any "B" cool. Other improvements that definitely help: RV8 exhaust headers, re-core V8 radiator to 4 row Corvette style rad. and lengthen 2.5" to the bottom of the rad.(bottom rad hose will need to be modified to accomidate longer distance)
Chris Longo

Martyn and Chris,

You both mention specialized fans, could you let us know where you found these fans, approx cost and maybe get pictures of them after installation? I can put pictures and write-ups on my website for all to see. Cooling is such a big issue, I would like solutions from numerous people available to anyone interested..
Larry Embrey

Hi all,

Just thought I'd add this. I have a Factory V8. She is uprated slightly with about 160hp I guess due to a Weber 500, different intake & 3.9L EFI Cam. I oil & filter change every 2000mls and use 20/50 whatever brand. I don't get any overheating problems at all. When in France with Paul & stuck in traffic, the gauge pegged at the fan cut in level and stayed there, but didn't rise past it. All I can say is the factory install can work, so long as everything is in top condition and correctly adjusted. The condition of the Fan motors would be a good place to look at, not to mention John's wiring advice which I'm going to try myself. Those fans suck a huge amount of juice!!

74 V8
Neil Cotty

As I am building an MGB GT V8 from scaps I addressed the heating problem with a vengence. I have Australian through-the-wings exhausts, a heavy duty radiator from D & D Fabrications and will be using a 14 inch 1,980 CFM puller electric fan from Revcor. If that doesn't do the trick - what will! I did find that the standard Buick water pump was 4" fat which was too "sticky out" for a big electric fan but I found a very nice chap in Los Angeles (the other side of the continent) who made me one only 3" fat (photo available on request). This gives tons of room to use the 14" Revcor whose pancake motor is only 3" thick .
Barrie Robinson

This thread was discussed between 28/12/2001 and 20/01/2002

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