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MG MGB Technical - Electric cooling fan

I am using the larger diameter harmonic balancer from a later car on my 1970 B. The car has A/C and the larger drive pulley runs the compressor (and engine fan) at a higher speed, allowing it to cool enough at idle to cycle.

The faster turning engine fan became noticeably noisy at speed, even with the overdrive engaged. Later cars came with two electric fans so this eliminated any mechanical fan noise.

The car has a 6 blade metal fan and I would like to replace it with an electric fan of sufficient capacity. Clearance is an issue, especially with limited space for the condenser which has its own 10" fan that runs when the compressor is engaged. The long nose water pump does not leave sufficient room for a "puller" between the radiator and the engine.

The question is what diameter electric fan is required to cool the radiator in slow traffic or at a stop, especially now in 40°+ ambient temperatures? The condenser can be set forward an inch or so which may provide sufficient clearance for Moss's Revotec "pusher" fan. The A/C's own booster fan could continue to run with the compressor but with both fans running together in a high heat condition, the draw on the electrical system would be considerable.

Suggestions? Some of this is clearly adapting a car designed for high latitude use to climate changing desert conditions.
Glenn Mallory

Have you thought of fitting a plastic fan?

I believe they tend to run quieter, due to the asymmetric spacing of the blades.

There is a thread about fans just below, entitled "Engine fan blade numbers".
Dave O'Neill 2

Glenn,
Dave beat me to it, have a look at that other thread.

For info I have a (uprated) Revotec "pusher" (blowing) fan on my midget, they're not quite as efficient as the other way also being on the front I find they can trap and hold some debris which needs an occasional clear out.

Something you might also want to consider, with mine at least when the fan is on and the car is stationary there is a drop in revs at idle as the (uprated) alternator does it's work and puts extra load to the engine. My 9" fan is about 8 or 9 amps load (then I guess there might be more for initial switch in start up(?)).
Nigel Atkins

if the plastic fan doesn't work for you, could you swap to a short nose waterpump and use a puller? I read there could be some smog pump limitations if you have that system.

I have an MGB aircon condensor here (not yet fitted) and with that in front of the rad the airflow thro the rad would be significantly limited already. Removing the mech fan and then (I assume) inserting an electric fan between the rad and condensor(?) in 40*C temps - Not sure what kind of cooling result you would get but I suspect it may be too limited. Fan could be running most of the time and even then finding it difficult to keep up. Have you checked out MGEXP? there are quite a few folks there with aircon B's who one might imagine have faced similar challenges.

I run a Davies Craig 11" on the B. They do high power versions in (I recall) 10 & 12" which pack some serious cfm - but also draw some serious ampage!

One good thing about the Davies Craig fans is they (mostly) can be wired as a pusher or a puller which not all brands can. That may give you some flexibility in the way you approach it.
Graham Moore

I removed the steel fan and installed two 9" fans in front of the radiator. The condenser is moved out slightly and now one the same plane as the radiator, which improves airflow over its original angled position. The condenser has a 10" fan that runs when the compressor is engaged.

The major improvement is in noise reduction at speed due to elimination of the mechanical fan. The A/C cool is also improved, indicating better condenser performance.

Engine temperatures rise slightly more to between the N and H position, about 3/4 over instead of the previous 1/2 to 9/16 needle position. But the car does not overheat, even after sustained climbing at speed on a hot summer day.

I will live with it for a while and if it seems that the two 9" fans are blocking natural air flow too much, I will try the Moss Motors plastic fan to see if it is quieter.
Glenn Mallory

Glen
Just a thought, 'maybe' try a few degrees cooler thermostat- it works 2 ways- no1 is that it'll open earlier at a lower temp, but also it gives the radiator a chance to do it's cooling job earlier before everything gets too toasty and out of control-
The std. thermostat temp is 73c (165f) and is the best for them
I've seen plenty with 180-185 's in them and they're ok on the road but as soon as they're under stress, -traffic or uphill the gauge rockets up just as yours is doing
Try a 73, you'll be pleasantly surprised
willy
William Revit

Thank you Willy. I have noticed that keeping ahead of a temperature rise seems to be a good strategy. I will try the cooler thermostat. There is one on the shelf.
Glenn Mallory

Usually 74c for hot climates, well over here at least. If possible I'd also have a fan or fans cutting in a bit earlier too with the same idea of catching the heat rise earlier.

I remember fitting a 'otter (hotter) switch that cut in sooner and it spotted the gauge needle going to the worry area of the gauge.
Nigel Atkins

Nigel-74c- thought it was round there somewhere
74c is hard to find here but 73 are plentiful as are 75
Don't think we'll disagree over 1deg c
Stay cool
willy
William Revit

"Stay cool" - stop it, Willy!
J P Hall

Ha ha John, best to not start Nigel off I guess
but, now that you mention it,
Stop It, is my favourite song for staying calm when things aren't going so well-it should be listed in the MG handbook -

https://www.youtube.com/watch?v=caGqOq1C84A
William Revit

Willy I wasn't arguing just putting what's in 'the book' though Glenn might have a wider choice of stat in the USA than we get in the UK. As you find it hard to get a 74c where you are here it'd be hard to find a 73c. Just one of the many differences between the UK and Taz (and USA).

I could just imagine some UK, at least, viewer searching for a 73c and I know you wouldn't want that on your conscience.

I don't think your favourite song would be in 'the good book' as it's missing a major component and even I could hear engine issues with that. 😁
Nigel Atkins

So harsh--
William Revit

🤣

I am now concerned that all those years of being too close to race cars and big V8s may have affected your hearing, have it checked before it's too late.






😉 😁
Nigel Atkins

Had a good one today
a lady's Midget that she wants a new c/w and pinion for
She reckons it's revving too hard out the road--did a lap in it and yep 5000@60mph and it felt busy but not that busy-checked the tacho and at 3000 it was showing 4500 and it'd buzz past 7 grand easy---Pulled it apart and tweeked him to match my master tach at 3-4-5-6- -back out the road and it's fine---crazy how a tach that's out plays with your head though, the car doesn't feel as busy now on the road, but it's exactly the same, but with a correct tacho reading.
Good excuse for a blast out the bush in a Midget though
Might have to recheck it again tomorrow before it goes back I feel- It's my duty
willy
William Revit

Yes, I had the same plays with your head thing when the voltage stabilser failed and the temp gauge was over-reading by 15 deg.
Paul Walbran

I was able to put the new electric fan configuration to the test yesterday with a 500 mile trip into central Chihuahua in Mexico. At speed, the car ran 3/4 to 7/8ths over towards hot with the A/C on full. Ambient temperature was between 90 and 100° F.

In afternoon rush hour traffic, the car boiled over once and quit in a busy intersection in Cd. Juárez with 95°F+ ambient temperatures, hot pavement, long traffic lights, etc., but fortunately started quickly and was able to keep moving w/o A/C. A bit hard on my companion and her dog. With the mechanical fan, the car typically ran slightly cooler, especially at speed so the two radiator fans must be obstructing air flow and are probably not quite strong (or large) enough to beat the extreme heat.

I think I will remove the electrics and try the plastic Moss fan once it is released from back order. Hopefully it will be quieter than the metal fan as the car is pleasant at 75MPH without the noise. The 10" condenser fan, which can also be activated with the radiator probe, provides some air flow boost to supplement a mechanical fan when the compressor is engaged.

in 1970, there was no provision for A/C and heat has crept up with climate change.
Glenn Mallory

As an update, hot running with no mechanical engine fan led me to order the Cobalt plastic fan from Moss. I removed the two electric fans that I had used as replacements for the noisy metal fan as they were obstructing air flow.

Finally, I managed to damage the radiator when changing the electric and plastic fans so I ordered an aluminum replacement radiator.

What a difference! The car operates in the low "N" range under a load, A/C on and 90°+ heat. Lessons:

-Air flow is critical. The large motors on the electric "pancake" fans obstructed about 17% of the total radiator area.

-The plastic mechanical fan upgrade moves more air than the metal fan and is quiet at speed. It also weighs much less.

-The aluminum radiator is extremely effective. My original radiator had been recored with a high capacity core but the aluminum radiator has twice as many vertical tube rows and a much tighter fin web between tubes. It is so dense that I had worried about reduced airflow but this is not a problem at all. Tubes and fins seem to be properly optimized.

-The booster fan on the A/C condenser improves cooling at idle. I disconnected it and the compressor cycle was considerably longer. The fan is set up to run at high radiator temperatures so that when the car is parked, it will clear out the under-hood heat that makes the Weber grumpy at hot startup.

-The A/C condenser is now mounted parallel to the radiator instead of angled against it to provide bonnet clearance. The clearance was not needed and the angle obstructed air flow.

The aluminum radiator and plastic fan makes all the difference. This is essential for proper summer running in the U.S. desert southwest region where A/C makes the car much more comfortable and climate change continues to move the original cooling capacity farther out of range.
Glenn Mallory

Nice one Glen--well done
i've never been a fan of electric aftermarket fans, the mechanical fans have done the job for years and are keeping things cool well before the electric fans click in---
Would have been nice to try the fan with your original radiator just to compare, but looks like you've got a good combo.
and Thanks for the update--all good info for the old memory bank
willy
William Revit

Actually, I did try the plastic fan with the original radiator. This was an improvement over the electric fans but the major difference was evident when the aluminum radiator went in. I had damaged the original radiator removing the ties that secured the two electric fans when the plastic fan was installed. That is when I ordered the aluminum radiator. The two combined (plastic fan + aluminum radiator) have totally improved the profile of the cooling system.

I am still driving the 1971 Midget that I got new. Even with a replacement radiator along the way, it runs 10 degrees F or so hotter than it did when it was new. Climate change? The Midgets temperature profile is in step with my 1973 Volvo P1800 and the 1970 MGB (prior to the improvements).

The original quest was to eliminate the noisy metal fan at running speed (75 MPH). It ended quieter and cooler with the plastic fan.
Glenn Mallory

This thread was discussed between 25/07/2022 and 12/09/2022

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