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MG MGB Technical - Supplementary cooling fan

I've been thinking about fitting an extra fan to the radiator of my 1979 roadster. The main reason is if stuck in traffic on occasions the coolant gets very hot and I lose fluid. Radiator has been flushed, new water pump thermostat and fan been replaced. Lots of fans on eBay from £12 upwards for 7 inch and bigger. Are these suitable? Would probably operate with a manual dash switch.
Which size would be recommended?
AdrianS

Adrian. you mention "the fan". does this mean your car has one fan only.?? If so, I suggest your air cooling is not as effective as it should be. Also check your radiator cap pressure.

My U.S. 79 MGB has twin 10" fans (measured tip to tip across) thermo-switch controlled. They are quite effective given our 90F+ (32C+) temperatures and humidity to match. You should be able to locate a set on line.

Cheers

Gary
79 MGB

gary hansen

UK spec cars only had one fan.
Dave O'Neill 2

Adrian,
Personally, I would not fit a second fan. There is some troubleshooting you could do to the cooling system to find out what is wrong.There are plenty of late MGBs running in the UK with the standard electric fan without overheating issues including mine.
Cheers
Craig
1980 MGBLE Roadster
C Harvey

Adrian, what Craig says makes sense and I would fully investigate why you lose fluid - where are you losing it from? If you still want to fit an additional fan, like the USA cars, then there is one for sale on ebay at the moment for £35 plus £5 postage.

http://www.ebay.co.uk/itm/LATE-MGB-ELECTRIC-FAN-FOR-RADIATOR-FULL-WORKING-ORDER-/322614254152?hash=item4b1d4eda48:g:TVoAAOSw6B5Zd3qu

If you fit it as an additional fan with a manual switch, the I would recommend you switch it via a relay as they take quite a bit of current.

Andy
Andy Robinson

Adrian,
Just have a look at one of the other posts relating to "rubbish parts", particularly water pumps. I've never had an issue running one fan, but these were after-market items, or second hand from other vehicles, not the standard one, which I think is not the most efficient design.
Sometimes the cap is an issue, not just the operating pressure but the "throat" length. I recently fitted a new cap and had the water loss problem. Turned out the length was too short, although sold as correct............rubbish parts again I'm afraid!!!
Allan Reeling

Thanks for the comments.

I did fit a new water pump 2 years ago and that improved the cooling somewhat. The old pump was alloy with a plastic impeller of which only half was remaining! I also flushed the system out and the radiator ( back flushed it ) and fitted new thermostat and radiator cap.

During general driving the temp needle sits steadily in the middle of the gauge. if I let the car idle for a prolonged period of time the electric fan kicks in but on several occasions water has been forced through the overflow pipe. I have bled the system carefully thinking that an air lock may have been responsible but just have that fear if stationary for a long time in summer that I may overheat the engine.

I suppose I should change the rad cap first and possibly the thermostat. I had thought about changing the radiator but the existing one is water tight and the flow seems good through it. The fan option was just for added peace of mind. However I am also aware that the extra fan would restrict airflow a little because of its presence so may induce more overheating!
AdrianS

My brother-in-law had the same type of OE electric fan (as shown in the ebay ad), on his 77 MGB (No engine Fan) and when he got stuck in a traffic jam for a few hours, the car overheated enough to cause the head to crack.

After he fitted a new head we removed the small standard fan and replaced it with a Revotec 10" fan which very obviously moved much more air through the radiator.

His car runs much cooler now with no signs of overheating.

When I first saw the tiny fan fitted to his car I thought that it had been fitted by mistake as it looks it would not be up to the job.

I use solely electric fans to cool my MGA but I have had to fit two 9" fans to make it effective, but the B seems to be fine with the single fan.
Colyn
Colyn Firth

Those yellow fans were not efficient at all. They put two of them on the V8's which always ran hot. I have 2 V'8's. A 3.9 with two 9" Revotecs and a 3.5 with the two original yellow fans. Guess which doesn't overheat and is quieter. Soon to be remedied!
Allan Reeling

My experience with my V8 conversion is the opposite. I had two 9" Spal fans on my car and they really couldn't cope with continental temperatures. Plus the size of the flat motors blocked a significant portion of the radiator.

I tried a very crude test of how much the fans could move a thin piece of paper which I held behind the radiator. The Spal fans blew it out at about a 45 degree angle. Substituting the original twin V8 fans had the paper standing out horizontally. To me the original fans were at least as good as the Spal fans, and possibly better. Plus the small area of the motors' body means less restriction to air reaching the rad.

The car still gets hot in traffic, and any amount of driving below 35 mph will have them on most of the time, but it never becomes critical. With the Spal fans I did see the water temp gauge enter the oil gauge scale and point to about 2 o'clock. It didn't boil over, but I would rather not see it up there.
Mike Howlett

Mike,
If it has gone off scale, it should be boiling over, unless it's sitting in an air or steam pocket.
I recently installed a TVR, high flow, thermostat on the 3.5 and that has made an incredible difference to the running temperature.
Allan Reeling

Allan, my gauge is a capillary one calibrated in degrees F. The max it shows is 230, but it went well past that to about the 2 o'clock position as I said. But with 4-life coolant, which says it won't boil until 180 C (356 F), and a 15 lb cap it was never going to boil. The header bottle couldn't have been completely full or it would have overflowed, but I lost no coolant at all.

Obviously I couldn't take a picture while stuck in a traffic jam, but the yellow arrow on my picture shows where the temp needle got to. The engine showed no distress at all and the fuel injection ensured that it still ticked over nicely. Oil pressure was still around 25 - 30 psi at idle. Once we got moving again everything returned to normal.

The car may have been fine, my wife and I weren't! It was 36 C in the shade and sitting in a GT without air con was no fun at all.


Mike Howlett

Mike, I'm impressed in two ways, 1. It didn't boil over and 2. An Idling oil pressure of 25 - 30!!!!! WOW!! Is this a Rover V8??
Allan Reeling

Yes Allan, it's a 1991 Range Rover engine, 3.9 litre with hot-wire efi. It is a very similar spec to an RV8 engine. It has covered about 30,000 miles since I rebuilt it and put it in the MGB GT. I have read of these engines sometimes having almost immeasurable oil pressure at hot idle, but mine never goes below 25, and never above 40 psi. My photo above was taken with the engine fully up to temperature and idling at around 800 rpm.
Mike Howlett

Mike.. We've been in 30C+ temps here in Florida for the last month and a half. Hopefully soon the pattern will break so we can enjoy the MG again. Dealt with fuel vaporization and engine compartment heat dissipation for a good part of it. To improve air flow, (suggestion from Chris @ Octarine Services) removal of the rubber seal from the perimeter of the engine compartment was a huge help.

Cheers
Gary
79 MGB
gary hansen

Done that Gary, and I've also drilled holes along the back edge of the bonnet (hood). I think getting the hot air out of the engine bay is the main problem with V8 MGBs. The space is so full of machinery all the hot air has to go downwards through whatever spaces are there. I have thru-the inner wing (fender) headers which help a lot.

For us here in the UK it's nice to have 30+ temps for a week or two while abroad on holiday, but not all the time! Mind you, today in SW Scotland we have rain and 16 C, and it's supposed to be summer.
Mike Howlett

Mike. It's very interesting ,my 3.9 does run cooler than the 3.5. They both have RV8 headers and HIF 6's..
I suppose the 3.9's have less aluminium around the liners which may help in heat dissipation to the coolant. Also your EFI will deliver the right mixture all the time, whereas carbs can be variable, similarly accurate timing. If they go lean the temp rises as it does with pinking.
Where is the temp gauge sender located?
The other variables, of course, are the gauges themselves.
Still not convinced by the 25 - 40 psi. What oil do you use? Did you keep the crank driven oil pump?
Allan Reeling

Allan, the temp gauge sender is plugged in to the casting between the RH cylinder head and the thermostat. There was a convenient threaded hole there. The gauges were brand new from Speedy Cables. I got the matching set when I built the car 9 years ago.

As for the oil pump, it is the standard item for that engine. The oil I have been using since it was run-in is Valvoline VR-1 20-50.

The Efi is just brilliant. So easy to wire in, and it worked right away, as soon as I turned the key. I have fitted an Optimax chip into the ECU. Why anyone would bother with those horrible 4-barrel carbs beats me. Despite the Efi kit being 26 years old, the car starts easily, hot or cold and never misses a beat. I did have the injectors properly cleaned, but in the last 30,000 miles nothing has been done to it at all.
Mike Howlett

Mike, If you've got the standard oil pump you will have the far more efficient crank driven pump, which explains the pressure!
Allan Reeling

This thread was discussed between 20/08/2017 and 26/08/2017

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