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MG MGB GT V8 Factory Originals Technical - V8 Cooling

Looking for some cooling recommendations.

I just registered my MG with the 3.5L V8, and driving it to emmissions test, the engine became quite warm waiting in line. Ambient here is about 80F during the day, and I anticipate cooling problems during the summer when temperatures can get in the 110-115F range. I'm using fuel injection, if that makes ay difference.

The radiator temperature reached about 200F. The radiator is a four row heavy duty unit that is about 4" longer than a standard MG radiator. The only cooling that I currently have is the two yellow MG fans, and when I feel behind the radiator with these two fans blowing, there is very little air. In addition, at freeway speeds these fans seem to block the air going into the radiator, and my temperature climbs into the 200F range.

I've looked at both electric and engine driven fans, and don't know what will produce the best cooling effect. Clearance for a 'sucker' type fan is quite limited, but I could get an addition 1-2 inches by moving the radiator forward.

Would appreciate any advice from those of you that have gone down this path before me, either with electric (sucker or pusher) or mechanical fans, shrouds etc.

Thanks for your help

Phil in Phoenix

Phil Dooley

The problem with overheating is a much talked about topic in this BBS. I am still fighting the same problems also with the 2 original fans and 4 row new radiator. Try installing louvers in the hood to get rid of the heat. Go back in the archives of this thread to find some more details.
werner van clapdurp

I don't have a B V8 but do own a 2.8V6 midget and cooling is an issue I have some experience with. The main problem with cooling fans is lack of adequate ducting to maximize their efficiency. If your fans don't have a ring around the out side of the blade and touching or almost touching the radiator then they will loose much of their airflow to the side instead of through the core. The air is going to go the the area of least pressure or resistance instead of through the core. The fans should not hinder the air flow at speed, the high pressure at the front of the car is much more than the fans would put out and the air will simply flow past them. In fact, they will turn even if no power is applied. My car uses a B radiator with a single 12" electric blow through fan which is fully sealed to the core. I vented the rear edge of the hood and when the fan kicks on you can feel the airflow at the top of the windshield. Even in 90+ degree heat my temp never gets above approximately 210 degrees. I installed a 190 degree fan switch and even at idle in traffic I don't have any problem.
I do recommend an oil cooler if you don't have one, as this removes some of the cooling load from the radiator.
Bill Young

Just a thought - did you connect the fans the right way round?

Sometimes the fan blades get put on back to front and they are less efficient that way - the concave face of the blade should face the radiator and the fan should rotate anti clockwise viewed from the front of the car.

I have the twin fans on my conversion and there is a very strong blast of air through the radiator.


The factory cooling fans are pushing air in the right direction, but very little air is making it through the four tube radiator.

Based on the archieve search suggested by Werner, it looks as though a shrouded pull through fan combined with ducting on the inner fender wells to let the air out would be a good start (would like to keep the car dead-stock looking on the outside, so I'm not considering louvers in the bonnet (yet)), followed by sealing the area surrounding the radiator to take full advantage of ram pressure rise at the front of the car when moving.

I've looked in Summit and Jegs, and there are several fans that look good.

Can anyone recommend a brand and size they have had good results with on a V8 B?

Phil Dooley
Phoenix, AZ

I use a crank driven flex fan, however, I am considering putting a fan clutch on it. The aluminum extension from the damper (custom machined) pretty well centers the fan on the radiator, and spaces it out just beyond the water pump. A fan shroud is a big help.
Jim Blackwood

Would you mind explaing this a little more "I vented the rear edge of the hood"


Bruce Mills


I agree with your assessment of the airflow through the radiator. With the engine compartment open on most cars, the fan blows with a very strong force. The stock duel MG fans blow the air outwards rather than through the radiator. Using aluminum strap I built loops shaped like the Greek letter Omega to surround the stock fans. This resulted in a slight improvement in the air going through the radiator, but much more air went beside the radiator because the fans extend past the sides of the radiator and I hadn’t sealed them there. I really wanted to keep the stock fans to keep it as much like MG did the original, but I wanted to drive a functional MGB V8 even more so I installed a 14” after-market electric fan. I can’t remember the brand, but it had the best blade design. The blades are curved which looks like they would trap the air better and the are self shrouded with a ring running around the tips. A second shroud is part of the fan guard/mount that attaches to the radiator core. The fan is rated to move 1200 cubic feet per minute and feels like it could blow a toupee off… until it is mounted to the radiator. The air passing through the radiator is considerably improved over stock, but still minimal when compared with other cars. Using the stock MG gauge indicates it gets warm, but stays steady at freeway speeds. The gauge pegging boil-overs come when it sits at idle in traffic. Air blowing off the front of a radiator will not remove much heat from the coolant. Now to compound the problem, without the air moving through the radiator, the air in the engine compartment doesn’t get displaced. Even when heated by a 200 degree radiator, the air passing through the radiator is much cooler the stagnate air being cooked by the exhaust headers and then being pulled into the carburetor. With the engine compartment hot enough to melt plastic, hood louvers must be considered. I am more intrigued at someone’s suggestion of fan boosted vents into the wheel wells.

George Champion

My personal theory is that one of the best methods of cooling an MG V-8 is make provision to get the hot air out of the engine bay. On my '74 V-8 (Olds 215 hi-compression motor)I am using a 13" aluminum mechanical fan on the water pump and have the two stock MG electric fans for back-up. The radiator is a bone stock 1978 MGB unit. Instead of dimpling the inner fenderwells for exhasut manifold clearance, I cut the metal away. This left two ovals about 4" high x 12" long in the fenderwells. I painted two layers of aluminum gutter screen black, and pop riveted the screen to the outside of the fenderwells. I know that sounds crude, but it actually looks pretty good, if done neatly,and most importantly, offers excellent airflow through the engine bay. As the area around the tires is actually a low-pressure area when the car in in motion, the hot air is literally being vacuumed away from the engine. In many years of driving, I have not overheated once even when trapped in traffic on 95degree days. The electric fans do come on occasionaly, or I will manually switch them on if I see that a traffic jam is ahead.
Kurt Schley

Getting the heat out of the bay is the bugbear and Kurt's mod is standard on the RV8 (additionally the pipes exit there as well). Try taking some fan running and not running times, one set with the bonnet up and the other set with the bonnet down and see the difference.

The standard pusher fans are chronically inefficient, even in the UK on a 'hot' (95F) summers day my gauge gets in to the red if stuck in traffic long enough even with both fans running full-time. Again, the RV8 has a very thin, large diameter, puller fan, but I think the rad is even further forward to get the extra clearance to the pulley.

I fitted a standard-sized but 25% uprated rad to my factory car and it has made a decent difference to how quickly the temp gets back down to normal after sitting it traffic for a while but has made less (indecent?) difference in traffic. The fans do not make any significant obstruction to the airflow while moving forward - the heat extraction (both from water and bay) is far more efficient than the fans even at slow road speeds - unless travelling in close convoy behind a large truck.

Paul Hunt

Do you baffle your fenderwell vents in any way to keep water and such from splashing in?
Jim Blackwood

The easy way out to keep the temperature down permanently is to louvre the bonnet. I have seen this done in Australia on a MGB - it also looks great.

My own MGB GTV8 has some heating problems in the summer - a new radiator improved matters.
Kevin Herbert

can u please tell me more about venting the inner fenderwells?
When moving the hot air escapes thru that area but when the car is still in traffic does is still escape thru there?

Or is it better to vent the hood ( bonnet) which will make hot air escape during idle but not when the car is on the move?

And also what happens about debri coming thru like water from the tires etc

steve berno

Just to add my twopennyworth on this topic - I have a standard V8 rad in my 3.5l conversion, together with standard twin fans - tubular exhaust manifolds, no vents, rear bonnet seal in place. I get really good cooling from this set up, my only concern is that the "Otter" type fan switch does not switch the fans on until well up the High end of the temperature guage but, once on, the fans pull the temp back to N within a couple of minutes - even stationary in traffic on hot days. (Even is S France & Spain on hols).

While doing the conversion ( on a 1973 roadster) I noticed that the fan motors available varied considerably and the ones currently supplied by people like MGB Hive are in fact units to be found on FORDs slightly modified. These motors are somewhat longer than the originals and draw almost twice as much power.

Perhaps this is the reason for the adequate cooling I have. Anybody else out there experienced similar?

Where can one have the bonnet louvered? I'm thinking of something like the Le Mans kit on some of the earlier Austin-Healeys -- i.e. 2 rows of louvers each about 8" wide, all the way up the hood. If this could be pulled off neatly, it would look absolutely killer and be very effective in getting rid of hot air. Has anyone had such a thing done? ... how'd it come out?

Harry, check your local phone book for companies dealing with Street Rods. They should be able to give you a reference for louvers in your area. Also check your local paper for adds or event notices about Street Rods. Most come with a contact name and number, and a call could get the informtion you want.
Bill Young


I also converted a roadster with 3,5l V8 and my 1977 car is a rubber bumper model. After the V8 conversion, i also converted it to chrome bumper and the cooling problem is not there any longer. The rubber bumper covers a great part of the radiator which restricts the air flow threw the radiator
Peter van de Velde

I agree with Peter van de velde rubber bumpers restrict air flow, i converted my 76 B to crome bumpers, 2 rows of louvers on the hood 11 each 5" wide they look great, radiator is early falcon/mustang v-8 the core dimentions are 17.5 x 16 = 289" of area. 13" mechanical flex fan when i fire up my car is like a typhoon of hot air coming out through the louvers, i feel it on the drivers seat. No cooling problems even on a 105 deg. day up the steepest mountains of Idaho. compared to the radiator of my 63 skylark whith the 215" v-8. dimentions are 23 x 12.5 = 287.5 is almost even. It is ok. to try to keep your B looking stock, but it is not fun see the temp. needle pointing to HOT. give me louvers any day.

I'm at the body modification stage of my '67 V8 project and i'm wondering if innner wing louvers located at the back of the inner wing would be as effective as hood louvers? I'm going for a pretty musch stock look on my project.
Chris Jones

I don't beleive that 200 degreed F can be sonsidered too hot. I currently run 73 B with a modified 4.6 with exit through fender headers.Radiator is Modine (old Mustang) that drops slighty below front apron. No other front body modification. Most factory modern radiator fan switches don't ground until about 200-250 degrees 225 being the average. If your radiator overflows/overheats before even reaching 200 degrees you might consider a larger capacity radiator. An engine is more efficent/powefull at higher temps (assuming you don't melt anything!) Enough babbling though. My concern is that the intake manifold temperature is too high for optimum performance. I need cooler air, but do not want to use a scoop. Although hood louvres could help a little, I am pondering the idea of using the factory fresh air vent (grill just ahead of windshield) as a cold air pickup for the carburetor. Kind of like NASCAR uses. I'm thinking of a sealed enclosure on top of the carb that leads to the back through the firewall and up to the fresh air vent. Has anyone ever tried this , or am I just crazy?

I would like to add to all of the excellent suggestions that a 160 thermostat is required to help in matters about cooling, also radiator cap pressure. One of the must important factors in air flow trough the radiator is the fan and shroud construction. Make the shroud as far back possible from the radiator and cover at least 90% of rad. The fan shroud should be as big as the shroud, one 1/4 of the fan should be visible outside the shroud.
Why? if the fan is install inside the shroud 100% it will develop a vortex between the rad. and fan keeping the hot air trap. Alot of testing was conducted in this area for the industry. Next is to get the hot air out of the engine bay. Two ways; one and the must efficient is trough the botton or downward (side louvers). Hood louvers are good for high speed drawing the hot air out, it all depends on the design, if you were to have louvers you will feel the hot air comming inside the car, in and around the winshield. The first can be achieve by vents, air ducks, side louvers, and fans. the second
ofcourse are louvers openings facing rearward and as far to sides as possible to the high volume areas of hot air.

Aluminun radiators are excellent to disipate heat, ofcourse the sq area is important, next is the size of hot water return, and inlet and addition of expansion tank between the termostat housing and the radiator can contribute. Dont forget the speed ratio between the crank and water pump. Electric fans should always come in to service around 160 degrees and should have a shroud for heavy duty service. I found a set from a XJ6 jag two fans like the B's with shrouds. If you would like to see an efficient cooling system, go find a 1985/90 Pontiac Trans Am, no grill opening a good electric fan design, functional hood vents and side vents.

An efficient engine should run around 180/200 degrees
It also depemds on engine compression, ratio of air fuel mixture, and timing, also type of engine paint and colour makes a difference in heat dissapation.

Chrome Vs Aluminun also makes a difference.

r/Bill G.
Bill Guzman

I had temperatur problems with all my rubber bumpered V8's. I think it is a problem of air intake. Chrome bumpered cars are better.
On my "JagEater" I use an RV8 radiator together with an RV8 fan, which is much more effectively than two MGB fans.
I also have the RV8 style exhaust manifolds inside and in normal use the fan don't work.
Only in hot whether and hard use the fan is needed.

Kepp firing on eight!
Juergen Felske

I've just completed a 1500 mile trip from Sydney to north of Brisbane & back. The ambient temps were in the low 80s F. I got caught in a few linebacks due to road works, but the result was the temp. never got above normal & the Rad. didn't need topping up once.
Just prior to leaving I punched 3 rows of 3, 1"dia holes in both inside fender walls as far back as I could. I half expected to find the engine bay filthy as we drove through some really heavy rain on 2 occasions ( I now know the windscreen needs sealing ), but there was no dirt at all. The car is a '71 CB Roadster, stock V8 Rad. stock fans, but Suzuki motors. ( I don't know the RPM ).There's a 10 row oil cooler & a trans. cooler in front of lower Rad. There's also 2 slots cut in the valance similar to the later models.I know the ambient temps. weren't very high , but I'm still pleased with the overall results.
Barrie E
Barrie Egerton

The cooling in my rubber bumper BV8 was helped by the addition of louvres in the bonnet. You can see how they look by going to the Gallery page of my website:
When I convert to RV8 headers later this year I don't think I will need the louvres.
They look good to me but they allow too much water into the engine bay when it rains!

Joaquin. One of the
robert pulleyblank

Joaquin,one of the US V8 owners has done exactly what you suggest ie bringing air in from the fresh air
vents in the bulkhead. He sent me some pictures of it. In general you will get a major power increase if
you manage to get fresh, cold dense air to the carb. I use 4 barrel Holleys on both my V8s, with the
horns cut off and the choke mechanisms removed.. I have as deep a filter as possible with a bulge in the
bonnet on the roadster. In order to get cold air to the carb of course you have to get the hot air out from
under the bonnet! I have Ford Escort Cosworth plastic louvres let into both cars bonnets and in addition,
the RV8 style manifolds exit through big holes in the inner wings. My friend and bodywork man
strengthened the rim of the these holes and fitted captive nuts around them to allow me to bolt on
stainless steel shrouds to keep the crap out in winter. Of course, Im in Florida in Winter but its the
thought that counts! Somebody somewhere told me that Austin /Morris 1300 heater fan motors will do as
rad fan motors. Never tried it Im afraid!
The cars never get hot on the move, only when stuck in traffic. The thermostat normally switches the fan
on but I fitted an override switch just in case on. The GT is a factory V8 rubber bumper with a much
modified 3.9 by the way.Id like to replace the rubber bumpers with fibre glass copies, never mind cool air.
Id be happy losing 200 lbs!
robert pulleyblank

Robert, thanks for responding. Off the subject,but.. Right now I run without an air filter because I find that a lowrider air housing assembly coupled with a thin filter does not allow enough air into my engine. The engine starves for air and the fuel ratio dramatically drops and makes the engine uneager to rev. I made my own motor mounts , the engine sits as low as possible, but I had to make a one inch thick adapter between the intake and carb. This was necessary because the base of my perf. AFB carb is much wider than the offy. intake base, but further moved my carb up. If I don't install my supercharger on the car I thought that getting air from the vents would be a cool (no pun) way to solve my problem by allowing me to make a rectangular air filter assembly. If I install my supercharger it would be easier to grab fresh air from the bottom of the car, between radiator and engine via a tube with cone filter.

Joaquin, cut the horn off the Carter, if you can. It will breathe much better. Running without an airfilter is a bad idea!
robert pulleyblank

I have an Olds 215 in a '69 "B". I use a mid-sixties mustang or falcon radiator (2-row, but tall) mounted within two inches of the hood latch support. Mounted directly to the radiator, pulling, is a Derale electric fan 16" in diameter. The fan in four inches thick, but pulls 1900 cfm and cools my car well. You can order the fan at Part # DER-16516. Good Luck!


I converted my MGB a few years back and used the original GT V8 carburator set up. At that time i could not get the original MG intake manifold so i modified the Rover manifold. I cut of the original carburator connextion point and instead of using a plate i let a welder weld up the aluminium manifold so that the plenum to carburators fitted. After welding i needed to let it machined flat. To avoid warping of the manifold it was mounted on an old engine during the welding. This method worked very well and it avoids using a plate which increases the height.
Peter van de Velde

This thread was discussed between 08/02/2000 and 14/03/2000

MG MGB GT V8 Factory Originals Technical index

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