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MG MGB GT V8 Factory Originals Technical - V8 Radiators

I'm looking to see if any V8 owners have experiance of aluminum alloy radiators.
I have a 1975 factory BGTV8, and suffer from hot running (but as yet no overheating) when the car is moving very slowly in heavy traffic. At normal road speeds driving at any speed between 40 - 90 mph, there is no problem with the coolant temperature, and the temp. gauge needle sits at normal. However after a very short time moving slowly in heavy traffic, the temperature rapidly increases, the cooling fans cut in but they will run virtually constantly, and do not seem to be able to reduce the coolant temp. significantly.
I'm told that this problem is common to most original BGTV8's. When moving slowly, and therefore having no "ram air movement" through the radiator, the very tight underbonnet space, with no cooling slots/louvres give the standard twin electic fans a hard time in removing heat from the standard radiator. My cooling system is in good condition, the standard radiator is fairly new, and both it and the engine have clear waterways. The thermostat works OK, as do the twin electric fans, and I run on about a 40% antifreeze mix in the coolant. I have the original cast iron exhaust manifolds. I know that its possible to fit RV8 exhaust manifolds by cutting slots in the inner wings, but I really don't want to carry out such a drastic modification to the shell of my original V8.
I met a V8 owner yesterday that had fitted an aluminium radiator, and said that it had improved the cars cooling system enourmously. He said that once the fans cut in, the temperature was reduced to normal far more rapidly that with the standard V8 radiator.
The aluminum V8 radiator is expensive - the best price I've found is 440 GBP. Does anyone else have any experiance / advice with this type of radiator?



Sorry I can't answer your query, but where in Nottm are you? I run a pub in Lenton, and my business partner has a 'B V8, so he may be able to help.

E-mail if you prefer.

Regards, Sim.

Adrian, Here in Los Angeles the temps. often exceed 100F. and cooling is a big issue. Antifreeze is not a very good coolant. Minimizing it's concentration will help some, I use 15% for corrosion protection. Fans are rated by cfm and amps., more flow can be gained by a bigger/stronger fan, venting the engine compartment with louvres or ducting. Mixture and timing I am sure you know, will also effect engine temperatures. My mechanic here in California does ducted-exhaust fan installations to help under bonnet cooling, buy pushing air out thru the wheel wells. Of course some people advocate thermal blanket wraps on the exhaust manifolds but, there is some issue with over heating damage to the manifolds themselves. Although I believe this to be more of a problem with headers at the first right angle turn of each tube. If there is room an oposing fan on the side of the radiator oposite the stock fans will assist flow too. Some of the archives of other than MG V8's, will have some good ideas for you too. Stay cool! Marc
Marc Judson

It was 109F here yesterday, and I was forced to drive my MG V8 about 30 miles accross town at about 5PM, the worst heat of the day. My other car has a outside air temp probe in the air inlet tract, and it typically reads 120-125 in traffic on black asphalt on days like yesterday. It wasn't my choice to drive at this time, but since I had to, I stuck a thermocouple between the upper radiator hose and the gooseneck on the thermostat housing and put the Fluke meter on the seat beside me so I could observe the temperature.

For most of the trip, the temp indicated between 170 and 180F. When I would stop at a long light, the temp would climb to about 180-185F, but within a half mile or so of moving it would be down to modulating at 170-175F. Once it managed to get up to 190F at a very long light. There appeared to be a 4-6F hysteresis in the action of the thermostat.

It is interesting to note that at 170-175F the needle on the gauge was almost dead center in the range, but on the excursions up to 190F or so, the needle was about an eighth inch from the red zone on the gauge, but the car was far from being in danger of overheating. I makes me wonder if a lot of the perception of overheating is the steep gain on the MG temp gauge.

I've a stock 3.5L Rover with a hotwire FI (and thermostat), brass radiator with 4 cores extended 4", a pusher electric fan, and a dammed and ducted radiator. I run water and no antifreeze, but use a corrosion inhibitor and lubricant. Standard block-hugger headers, no vents in the hood or fenderwells, but I did take the rear seal out of the engine bay.

Emission inspection is in July, and I can hardly wait to sit in line outside for an hour. That will be a real test.

Phil in stinkin hot Phoenix.


And another thing.....

I was in Arizona Race Mart a couple of days ago looking for a radiator for another application. They sell an aluminum radiator they use in sprint cars and other circle track racers for $295, mostly used with small block Chevrolets. The counterman said he could also order custome sizes with your choice of inlet/outlet sizes and cross-flow or conventional. The brand he had was 'C&R' and one other whos name I don't recall.

They have a web site and ship all over the states.

If I have anymore solder bloom problems with my copper radiator, I think I'll order one and make my fan a sucker instead of a blower.

Frankly, your problem doesn't sound too serious although you don't say how high the temperature rises in traffic and how quickly it comes down again when you start moving.

There has been a lot of discussion on this topic so look in the archive. However here are some of the conclusions which you will come to when you read the archive.

Original fans are not much good - especially when they are old. They use a lot of power and are very basic in their design. They lack shrouds and are too far away from the rad and on the wrong side. People who do not have a particular cooling problem find them adequate. You should be looking for modern twin fans, shrouded, up close to the rad and if you can fit them or even one on the engine side of the rad you will have much more efficient cooling.

Anti-freeze does not aid cooling but it is not worth leaving it out as corrosion is a more serious problem. Also its deleterious efect on cooling is probably fairly small. It should be replaced regularly as the corrosion inhibitors wear out.

A wetting agent such as Water Wetter is helpful.

RV8 headers definitely reduce the heat problem and may improve performance too.

High performance rads are available. You can get a four core rad in copper which will help but even better is the ally rad which will be four core, and because you are having it made it can be a higher volume. Ally is a better conductor of heat and if you try to touch one in the car you will quickly understand that this is true.

I have a spare ally rad for sale. Contact me.
Marc Gander

There is an article in the July Car and Driver about a product from Zerex. It was called Zerex Racing Super Coolant and was said to just contain rust inhibitors. The article went on to mention by switching to this would increase cooling by something like 25%. But advised against leaving in during winter as it will freeze.


Changing to Aly rad seams easiest fix although I've not seen any Specs with those advertised MGOC Frontline. I solved my cooling probs by recoring rad and using Water Wetter. Ceramic coating manifolds should also help.


Gentlemen, thank you for your advice and input. Phil and Marcs comments are reassuring. As I mentioned initially, I don't have a overheating problem, but because of the rapid gain in the temperature gauge, and the inability of the standard fans to get the temperature down in traffic, I percieve that I have a hot running problem.
Phil - (un)fortunately temperatures in the UK are very mild compared to what you experiance. Today I saw the outside temp. guage in my R75 reach the dizzy heights of 22 degrees C - about 72F, and we don't have many days like this.

When I sit in traffic, or at a red light in my V8 for about 3-5 minutes, the temperature gauge moves rapidly from the normal position to a few degrees away from the red zone (about 4 o'clock position), the fans cut in, and if normal driving can be resumed - ie. speeds above 30 mph, the needle will soon fall back to normal.
If I'm stationary for more than a few minutes, or crawling slowly in traffic the fans run continuosly, and only move the temperature needle back by a few degrees. The fans cannot move the gauge back to the normal position, only air movement through normal driving will do that.

I'm probably being a bit paranoid about the temperature gauge getting close the the red segment, but I've become very sensative to potential cooling problems. I also run a Stag 3.0 litre, and despite the volumes of written material on the Stag's supposed dire overheating problems (HGF, warped heads etc) I find that its temp. gauge doesn't seem to move so rapidly and so closely towards the red segment compared to the V8. But the Stag's cooling system contains 18.5 pints compared to the MGV8's 16 pints. Also there is better ventilation in the engine compartment.

I think I'll try the alloy radiator combined with a more efficient fan setup, something like twin Kenlowes mounted close to the rad.
Marc - I'll contact you by e mail re. your alloy rad.



As one of the few (maybe the only) guy with a Factory V-8 in hot Northern California, I can attest to the problem that Adrian is experiencing. It is especially bad on a Factory V-8 because of the tight underbonnet clearances made worse by the Factory exhaust manifolds and induction system. I notice an even worse symptom - if the car is in slow traffic or stopped for any length of time in the heat, it will go into what Paul Hunt once described as "thermal runaway". The temp gauge will peg, with the fans having little or no effect on bringing the temp down. Interesting to note that during this entire process, the coolant never boils over. The last time this happened to me was during my dreaded California smog check, with the car on a dynamometer. The huge industrial fan that they set up to blow air in through the grille had no effect in stopping the inexorable climb in temp. All we could do was shut the thing down and wait until it cooled somewhat.

What we need is input from Factory V-8 owners in a hot climate who has had success with alloy radiators, different coolant blends, and the like. I don't want to put in obvious changes like bonnet louvers.

Paul Kile
Paul Kile

There is something to this 'thermal runaway' thing. I've let my car sit and idle for 20 minutes in the driveway on a hot day, and the temp gauge won't budge. Take it out on the freeway at 75 mph, hit the exit and stop at a light, and it will bounce up to 190F+ quickly. I think it has to do with how quickly an aluminum block can release heat and overwhelm the cooling capacity of the radiator. The ability of aluminum to conduct heat is much better than cast iron.

In my opinion the best configuration is likely to be a crossflow aluminum radiator, with the biggest shrouded fan on the engine side of the radiator running water with an anticorrosion additive and lubricant (or minimum amount of coolant to get through the winter).

The 'water wetter' product doesn't do much, in my opinion. Yes it will improve the ability of the water/antifreeze mix to conduct heat away, but the effect is rather small compared to what can be achieved by decreasing the proportion of antifreeze to water in the system. However, Jag owners in these parts swear by some stuff I think is called 'Zero' or something like that. I'd be very interested in any data anyone has on the ability of the new Zerex coolant as compared to water.


Adrian, I am just up the road from you in Newark and so experience the same weather conditions (assuming we are on the road at the same time). Like Paul I don't think your experience is unusual for a standard factory setup. For myself I find that the fans are only needed below about 20 Mph but in my case they do bring the temp down to below "N" provided the outside temp is not too high. I do have bonnet louvres though which helps to exhaust the hot air. AFAIK the rad is standard though it has been rebuilt sometime in the past - in fact it may be in need of repair soon as I get a slight weep from somewhere!). The only caution I would give about Ally rads is their vulnerability. They are more easily damaged which can hurt a lot when you consider the cost.
ian thomson

Slightly off-topic Im afraid, but I replaced the original radiator in my B (not V8) recently. When replacing it a comment Peter Burgess made to me last time I was up there made sense.
It seems that the original radiators had all the rows of tubes offset from each other, so that as you look through the fins you can see lots and lots of tubes. The modern replacement radiators have all the rows of tubes lined up, one behind the other. This means that the air flow does not hit all the tubes, only the ones at the front of the radiator.
The new radiator is by no means as efficient as the old one, and my car now runs very slightly hotter. (I had a hole in the old radiator, hence replacing it).
When looking for new, or replacement radiators it is probably worth looking out for the placement of the tubes, as this could have a big effect on the cooling properties.

Regarding Phils point about "thermal runaway" I've let my car idle on the drive, and it'll take at least 20-30 minutes for the temp to exceed normal and the fans to cut in. But sit at a red light after a drive at normal road speeds and the temp. rises much more rapidly.

Ian - the factory V8 has no bonnet lourves, but has a nicely sound (and thermally) insulated bonnet. The hot air has nowhere to go.

Anyway I take back all I said yesterday about the Triumph Stags overstated cooling problems compared to the MGBV8 - one HG failed today on my Stag factory 3.0L V8 so I'm very pi**ed off. I join the neverending list of Stag HGF over the past 25 years (sympathy to MGF owners with HGF). Please don't respond with "what do you expect with a Triumph engine" or I'll start ranting on about post 1975 midgets, and K series engines.

Anyway I think I'll probably go for the alloy rad + new Kenlowe fans for the MGB V8, when I've sorted the Stags HGF problem.



I have a similar problem with my 74 factory V8 - largely original except for tub manifolds. At speed the normal temperature is marginally higher than 'N' but rises very quickly at rest only to fall probably as quickly when moving again. However my Otter switch does not work and I turn the fans on manually - and generally leave them on all the time thereafter. I would prefer automatic switching so would be pleased to hear from anyone about alternatives to the 'Otter'.

Improving the cooling is my current project and I plan the following ...

1] Remove the thermostat to improve coolant flow - the car is only used in what passes as a UK summer.

2] Replace current 50% antifreeze/water mixture with 10-15% AF possibly with a water wetter.

3] Relocate horns to improve air flow to the fans/radiator and possibly even removing the oil cooler entirely. Not that difficult if anyone knows a UK source for a new pump-to-filter pipe.

4] If all else fails I would then consider a larger S/S header tank and/or an ally radiator.

I will report back on progress.


David Rawlence

The original "otter" switch is NLA for the V-8, but Burlen Fuel Systems in Salisbury markets a replacement for the original part number BHA 5252. I installed one of these in place of the original, so did Paul Hunt. The replacement switch appears to allow the fans to turn on slightly earlier and run longer before switching off.

Paul Kile
Paul Kile


I'd be nervous about carrying out points 1,2,& 3, and I'd want to take advice from a knowledgable V8 source before carrying out these mods. Because the hot running only is a problem in traffic when the car is moving slowly the advice on this thread seems to be to maximise the air movement through the rad. ie. more efficient cooling fans, and if necessary a more efficient alloy rad to aid cooling when there is no air movement when the car is virtually stationary.

Modern cars don't suffer from overheating problems compared to cars of 25-40 years ago, but they do have efficient electric fans to maximise airflow through the rad, and alloy rads that dissapate the heat more efficiently than brass rads. (and I suppose are also cheaper to make)

1. By removing the thermostat wouldn't it be detrimental to the engine in inital cold running because it would delay its getting up to the correct running temp?
2. I'd be worried about using such a low concentration of antifreeze (and therefore corrosion inhibitor) in the all alloy V8.
3. I wouldn't want to remove the oil cooler, oil is an important engine coolant as well as a lubricant. Whilst there are probably many Rover V8 engined vehicles running OK without oil coolers, it would seem to me to be a retrograde step to remove the oil cooler.
I replaced my standard oil cooler with a 13 row unit to help oil cooling at high engine speeds, but fitted an oil cooler thermostat.

I think my project will be to change the original fans for a Kenlowe setup, plus a four core alloy rad.



Paul, David,

I replaced my otter switch a few months ago, and the MG/Triumph parts centre in Birmingham (ex Moss) told me the same - original V8 NLA. Replacement was a P6 Rover switch and this appears to work just the same as the V8 otter.



Thanks for your help re Otter switch. I have now obtained one from Moss plus a new relay and all I need now is some idea of wiring so that I can retain the manual over-ride switch. Can anyone help ?

I am happy with binning the thermostat as I always let the engine warm up before starting off - a legacy of having manual fans and remembering to turn them on . In addition, despite the fans being on continuously, there is a tendency for the temp guage to fluctuate markedly even at speed. This I attribute to the thermostat clicking in and out and possibly it may be the wrong type. I'll remove it and see what happens.


David Rawlence

Wow - who would have believed an overcooled MG V8 !

Removing the thermostat certainly has much more of an effect that I thought. At road speeds it now runs on the cool side (nearer N than C) and when stationary the now automated fans seem to cope and kept the guage on 'N'. Admittedly it was not hot today (around 17C) and I would like to repeat the exercise if the UK summer ever arrives.

The thermostat tested OK and was rated at the recommended 82C/180F. This suggests that for average UK temperatures an 82C thermostat is too hot so I will be testing colder units (if available) to find the optimum between overheating whilst stationary and overcooling at fast road speeds.
David Rawlence


Running without a thermostat (usually replaced by blanking sleeve) may give an artificially low reading because of placement of sensor and mess up flow of water round engine with some cylinders now running hot.

A low water temp may mean that the oil is not running hot enough to function properly (needs to be above 80deg but should be near 100deg).

Would be useful for accurate water and oil temps.

From latest Castrol advert most engine damage occurs in first 10minutes when starting from cold, by removing thermostat you may be extending this period.



Thanks for your comments. I usually let the beast warm up on the drive for 10 mins before moving off - this probably burns about a gallon of gas but does allow the oil to warm up. However I do like the idea of assessing oil temp (if only to confirm whether the oil cooler is necessary) so where is the best place for the sensor ?

Removing the T/S suggested to me that, as over-cooling occurred, my best bet was to investigate different T/S temperature ratings. By chance I found a 78'C T/S, and this works exceptionally well - temperature at fast road speeds now remains at 'N' and the engine is sweeter and more responsive than previous. However, as a word of caution, I would suspect that all engines behave differently so I would not take my experience as gospel.

Unfortunately, having now lashed out 35 notes for an 'Otter' I have yet to encounter a long enough wait at lights to see whether they click in but I can live with that.

I have a question re oil grade - I have always used a good quality mineral 20/50 but Penrite recommend their 20/60 - it must be like treacle so has anyone any experience of this grade?

David Rawlence

David, because an oil cooler would be mounted after the oil filter, that is where I would mount a temperature sensor to a gauge if possible. It would be entertaining to monitor the temperture both before and after the oil cooler. Someone on this board said he saw one MGB V8 conversion that had an oil cooler in the battery area with a temperature-controlled fan. Having the oil cooler out of the air stream would alleviate concerns about overcooling and the fan would ensure heat transfer even in this hot location.
George Champion

There are devices out there that are temp controled to move flow from the oil cooler back to block etc...

Larry Embrey

Wide fluctuations of the temp gauge are usually caused by the bypass hose
from the thermostat cover to the inlet manifold being blocked. This stops
steam in air-pockets giving high temp readings - I have seen the temp needle
go as high as 40psi on the oil section!

Running without a stat is said to cause localised overheating as the
aperture that is left is much larger than with the stat in position even
fully open, and the water is now moving too fast and getting turbulence. By
lifting one end of the stat spring over one strut that supports the base of
the stat you can 'unscrew' the spring. First heat cycle allows the stat to
open to its normal fully open position after which it stays there, or you
can push it open by hand to start with. Screwing the spring back on again
restores the stat to normal.

Wiring diagrams of the factory system at then
click on 'Spanners', 'Electrics', 'Schematics' and 'Electric Cooling Fans'.

Recently had a 30% improvement in my fans by connecting additional grounds
to each fan from under its mounting bracket and running a heavy-gauge brown
from the spare output spade on the alternator direct to the fan relay.
Paul Hunt


The link doesn't work.

Could you check it and repost?


Sheesh -
Paul Hunt

As a side note on radiators, aluminum is not a better material than copper/brass for heat transfer. Copper/brass is a much more efficient heat transfer material.

The reason ally rads work better than most copper/brass is because the ally can support a larger tube with more surface area. This is because the aluminum is a stronger metal. Most ally rads have 1" tubes, the high performance versions have 1 1/4" tubes. If you were to make a copper rad with 1" tubes, the thicker materiel required offsets the better heat transfer properties.

A smaller consideration is the amount of solder required to manufacture a copper/brass radiator. Solder is a much poorer heat transfer material than either aluminum or copper.

I spent the best part of a year radiator shopping & in the process, talked to 5 or 6 ally radiator manufacturers, as well as a few conventional radiator manufacturers. Each will tell you their product is superior to the other. I found that a well designed copper radiator with louvered fins on the tubes in a 4 row design will cool as well as the same size budget aluminum radiator, but not as well as an aluminum radiator with 1 1/4" tubes.

Talk to the manufacturers out there such as Be Cool, Griffin, Howe & others, as well as a good local custom shop, if you are lucky enough to have one.

Cross flow seems to be the best design, but we are limited to 19" of width, which really eliminates this design, unless you cut & box the frame rails.
Jim Stuart

Jim, you are correct about the ally radiator, now if we could only afford a radiator made from silver.
An expansion tank can be installed in the cooling system. This is a tank that is mounted between the engine block and the radiator; this system is used on stationary industrial engines. The purpose for the tank is to pre-cool the very hot water before it enters the radiator, and ads extra cooling to the system, thus improving the cooling.
Don't run your cooling system without a thermostat. Use an oil cooler thermostat, and use the new coolant for ally engine blocks, such as GM red stuff (forgot the name, I have just experience a senior moment) Any way it does work.
On my racecar I use a copper radiator with a fine cooling fins and added expansion tank with an 18lb radiator cap, max temp on a very hot day in Aug is 210, which is ok, heck 230 would also be ok.

Bill Guzman

Just a comment on copper brass radiators. I drove home from work today, temp was 97', humidity over 90%, the worst possible situation for cooling. It is a 26 mile run, mostly on the beltway at 55-65 mph, with the end of the trip in heavy traffic & a number of long stop lights. With the air conditioning running full blast, water temp never exceeded 212', even stopped in traffic.

Engine is a relatively stock 215 with a late Rover front cover, 16" puller fan, 3000 cfm, 10" pusher that runs only when the A/C compressor is on, & a copper radiator.

The radiator has an expermental core, 4 row, with oversize tubes, 23 louvered fins per inch. It is based on a '77 MGB with the tanks modified as to inlet & outlet, 2" longer than stock, & I use a TR7 expansion tank.

The A/C is a modified Hot Rod Air unit using a Sanyo 508 compressor.

This thread was discussed between 17/06/2002 and 04/07/2002

MG MGB GT V8 Factory Originals Technical index

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