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MG MGB Technical - Electric Fan or Stay with mechanical?

The recent/running thread on this, specifically the Revotec, was very instructive and as would be expected with mixed messages about fans from those who have fitted them, but rather than totally hijack it , but at the risk of some repetition I thought a separate one on this might be better?

I am thinking of fitting one of these mainly due to an event we are planning on going for next year which will involve lots of miles at 30 mph or under in addition to several climbs to 6000+ feet. (and back down!) . Ambient local temperature will max out at about 25C

I have had no cooling issues up to now ( Chrome bumpered MG BGT ) , but I am fitting a new radiator just to be sure, quite large pieces of rust having come out of it when I backflushed it for the second time.

I have had mixed messages about electric fans – some think they are great; others have seen little benefit. I contacted someone who does classic car event mechanical support who said sort out what you have and do not bother – he expressed some concern on the additional strain on the electrics and the impact of failure (I suppose I could carry the old fan in the boot but it’s a bit of a pain!). Some rally entrants have them fitted.

So, if I fitted one it would be purely for better cooling in the circumstances described above, perhaps manually overriding it, switching it on before a climb or special test? Any performance gain would be a bonus but not a reason for fitting it. I am specifically looking at a Revotec pusher; an out of the box solution rather than making up my own system.
- Is the mechanical fan more than adequate for my purposes ?
- Would my cooling be improved with the revotec ?
- What are the implications of having both – does the revotec work better without the mechanical in place? Would the mechanical be less effective?
- Reliability is a factor

Mike Dixon

They never needed aftermarket electric fans while in production including desert states around the world, nor since. If you have a problem with cooling, then find and fix it.

I've been stuck in traffic on an MG run in very warm weather with a Midget behind me and his electric fan was running the whole time - which incidentally is loading the alternator and hence the engine the whole time. My temp gauge didn't get more than half-way from N to the edge of the H zone. In extreme conditions I've had both the roadster and the V8 on the edge of the H zone with no running problems or loss of coolant. The systems are designed to deal with that, people have become paranoid after driving modern cars where the needle stays bang in the same place no matter what.

A pal was planning a trip in the Picos mountains, and even though his 72 had kept its cool in 35C in the UK previously decided to fit one of the later factory 6-blade metal fans and had no problems at all.

Yes, an electric fan reduces losses when under way and ram-air cooling takes over, but if you were bothered about a tiny increase in HP and mpg you probably shouldn't be driving an MGB anyway. People get sucked in by the fear, uncertainty and doubt created by suppliers of this and other stuff.
paulh4

The mechanical fan will certainly cope with hill-climbing at 25degrees. If it overheats you can always put the heater on. To be serious briefly, we replaced the mechanical fan with a single pusher from the very early sixties - mainly in the pursuit of power. More powerful chrome 1800s running at higher compression on five star needed an electric fan - the rubber bumper obstructs airflow and made one electric fan a necessity.
Working on your last observation about reliability applied to the car, you might fit a single electric fan with a control on the dashboard. It might obstruct the radiator a little but would certainly improve the car's reliability at temperatures of 30 degrees plus.
We have fitted a manually controlled electric and kept the manual fan in our A - belt and braces after a long hold up on a Summer's day in the UK.
FWIW Roger
Roger Walker

25c -a nice cool day to go racing
Not an electric fan fan
We've been running a later 7 blade plastic fan for years--best thing ever, no fuses to blow or relays to die
A pusher electric fan will obstruct the airflow to the radiator when it's not on

Biggest mistake that B owners make is fitting high temp thermostats---I don't understand why-
Best choice is a 165f(73c) -perfect or 170 if the weather is a lot cooler
Run a plastic fan and a decent outside mass belt and it'll be bulletproof and make sure you've got a good seal between the top of the radiator and the support panel, most cars have a whopping gap there with no seal, and a good seal between the support panel and the bonnet, If your car has a steel bonnet then you'll probably have quite a gap above the seal for the air to go straight over the top
Work on the basics
Keep it simple
willy
William Revit

Mike,
my answer may surprise some, I'm a fan of electric fan over engine fan but I (used to) use my classic as a daily and through winters where the engine fan slows warm up - but as others have put the engine fan will do the job for you what is more important is to have you whole cooling/heating system clean and fully functioning.

Unless you've done so before that usually involves more than a new rad and drain and refill.

(If you've not had them before?) As you've probably seen before I offer notes of my very simple but thorough cooling system cleaning, email me if you want them, if only as a tick list.

Willy's idea of fitting a 74c (over here) warm weather 'water' stat may also help for your event. But do bear in mind if you don't have an oil thermostat fitted to your oil cooler then at times, especially with the engine fan, you will be cooling when not required, so slowing up warm up, or over cooling (perhaps excluding the event but other times).

Nigel Atkins

Whether to fit an electric fan or not is a personal choice. When I first got my 76 roadster, I was not happy with the engine temperature in traffic on warm days, as the temperature gauge increased very readily into the H zone. In normal running it would normally read about 25 to the hour position, or just to the left of the N. So I replaced the radiator to diaphragm seal (which was missing) and the bonnet seal and also the radiator. The cooling system was flushed and filled with 4Life coolant.

This didn't make a lot of difference, so I removed the plastic fan (now in boot, just in case needed) and fitted a sucking 10 inch Revotec fan. This improved things, but I was not happy with the amount of time it took to cool the engine and felt it wasn't quite up to the job. I change it out for a 12 inch blowing fan, which really did make a difference and keeps the engine temperature comfortably at about the 25 past the hour position even on the hottest days in traffic.

I also fitted a manual switch for the fan, in case of problems with the Revotec thermostat and upgraded the alternator to a 18 ACR, so it had plenty of capacity to run the fan. All personal choice, but works for me.

Andy
Andy Robinson

I have a 1980B rubber bumper with the factory fitted electric fan. The radiator is mounted further forward than with a mechanical fan. We live 1050 mtrs above see level in the KZN Midlands. Ambient temperature ranges from -1C winter on occasion to +35C summer, quite regularly. The temp switch mounted in the radiator has a Optional bypass switch, actually the same as the interior cooling fan switch from Moss. No relays . I fitted this 15 years ago. Goes in the switch panel on the dash in the spare position.
No problems on the open road and mountain passes with getting hot but at 30+ C in slow traffic keep an eye on the temp gauge and engage the fan before it gets too hot. At 2000mts amsl Johannesburg, no discernable variation in the cooling department.
Ray Bester

51 years and 250,000 miles in my bog-standard 1965 MGB with never a hint of overheating even in stop-start traffic in 35C (and higher) days in and around Sydney Australia. At one period of my life, day in-day out. (Above 35C it simply is too uncomfortably hot for the driver. In my experience, 40C plus however is not a problem for the car). Original mechanical fan, original radiator, no shroud and no supplementary or upgraded mechanical fan.

I am frequently bemused (and confused) by people's MGB "over-heating issues", and the resultant addition of add-on electric fans, mostly as "pusher" fans, to overcome their problems. I would think they need to sort the mechanicals first. In my own personal experience, an original spec MGB in good condition simply does not run hot.

I do however think the original mechanical fan wastes engine power, being often spun, sometimes at high speed, when not needed, and making additional noise.
T Aczel

Maybe a viscous fan would be a compromise?
Colin Parkinson

Something wrong if it readily goes into the H zone in the UK, which tends to be confirmed by the first electric fan taking a long time to reduce the temperature.

Either something is causing the engine to produce too much heat, or something is causing the cooling system to fail to get rid of it.

Did you ever measure the temperature of the coolant? Scan the radiator with an infra-red thermometer looking for cool spots i.e. a partially blocked rad? Compare the inlet temp with the outlet temp which would show low flow from the pump or obstruction from another source?
paulh4

Andy,
I think the same as Paul, standard set up clean and in good functioning condition should be fine for standardish model, as has been proved by the contributors here from higher and hotter climates.

The obstruction(s) could be in other places in the system to the rad (or as well as), though the rad would make a big difference.

Same as I put with Mike, a simple thorough cleaning of the whole cooling/heating system would probably help and certainly not hurt. You can save the 4-Life to reuse too (unless really contaminated).

I've got (Revotec) electric fan which when running provokes the 18ACR I have fitted which in turn takes away a little engine power, which between the two is probably greater than the engine fan but the lost is usually when you're not using too much engine power.

I've used (lots of) 4-Life for decades in classics and more modern cars.

I've always though a viscous fan might be a good idea but boy they can be noisy if not in good condition.
Nigel Atkins

Never bothered with anything except standard anti-freeze, which can be topped up with plain water in a pinch such as hose replacement on the road. A pal had For-Life, but it didn't change colour when his head cracked and combustion gases were pushing coolant out. Someone else tested it by running his exhaust through a sample and that didn't change colour either.

Others swear by Evans Waterless but Peter Burgess won't guarantee his engines or heads if that is used.

You still need to be careful with conventional antifreeze, which used to have the term 'glycol' somewhere but manufacturers in their wisdom have renamed Inorganic Acid Technology or IAT which of course has no chance of being confused with Organic Acid Technology or OAT. The two must not be mixed or it forms a crystalline sludge, or glycol-based with any of HOAT, P-HOAT and Si-HOAT, available in orange, yellow, turquoise, pink, blue and purple to suit your decor! Shades of brake fluid with DOT 5.1 not being compatible with DOT 5 whereas it is with DOT 4!
paulh4

Thank you all for your comments and thoughts - as noted above it is down to personal choice but informed input, of which this forum has an abundance, is always really welcome.

I think I am going to stick with mechanical fan. I have given the system a thorough flushing out twice now so I will see how that plus the new rad and fitting the missing top foam seal works for me.

I may fit a 7 blade plastic fan - I still have a metal 3 blade - but I have heard ( well an archive search to be honest) they are noisy?

I am also sticking with water/antifreeze, not least because I can always find some water if I need it.

All we need now is a hot summer in UK and some miles under the belt to give it a good test!
Mike Dixon

Electric every time.
1. Why put up with the noise of a mechanical when it isn't doing anything useful; i.e. above 12MPH
2. The multi-bladed plastic fans are surprisingly NOISY!!! They get noisier the faster they spin; i.e., when they aren't achieving anything.
I say "surprising"..............you can hear them over and above engine clatter and wind noise.
Allan Reeling

Mike,
did you poke out the engine block drain plug when you were flushing, some say it's a waste of time but as with a lot of things (crud, muck, rust, debris in this case) it's a lot better out than (still) in.

I always do back-flushes between cleans, flushes and drains and am careful to get out as much residue of old coolant (and crud), cleaner and flushes as I can at each stage because there's always a surprising amount of residue left in at each stage. Just measure how much coolant you put in and then compare it with dry fill capacity, the difference is the residue (same for oil changes of engine, bearbox and rear axle).
Nigel Atkins

6 and 7-blade fans ARE noisy but then the MGB is hardly quiet! When first fitted for Switzerland they were shortly withdrawn for that reason. I've never found the need for anything other than the standard 3-blade on my 73.
paulh4

Nigel - yes I do the same and took out the drain plug - as you say its amazing how much crud appears every time but its getting better.

Paul, thanks, I will leave well alone, and get the new radiator in.

Mike
Mike Dixon

The plastic fans do whistle with spirited driving but keeping them whistling is all part of the fun

The thing is Mike was asking about cooling for climbing several hills up to 6000ft at under 30mph
Doing that sort of driving the plastic b fan would be perfect

Also ,Paul has thrown in coolants
Do some reading on what you're thinking of buying and make sure it's compatible with the solder in your brass radiator and heater core

willy
William Revit

Mike,
I also use a bit of stiff wire to loosen any crud out of the engine block drain hole at draining and flushes.

If your rad is out perfect time to back- flush and then forward flush engine block and to flush, back-flush and flush again your cleaned heater matrix and any pipes and hoses you can easily get off the cooling/heating system.

By cleaning and flushing you can cause crud/dirt/debris/gunk to also migrate from one area to another so if you give the whole system a thorough cleaning it will help to expel or at least cut the migration down.
Nigel Atkins

Best drained warm. When mine obviously needed flushing looking in the rad was bright orange when warm, but clear green when cold. Implying muck was being stirred up when running and settled out again when cold. The rad when removed took many partial fills and vigorous agitation before it started to come clear. Less easy to do that with the block.

The most I got out of my block (blocked, more like ...) drain was a mucky dribble despite much poking. Some have said they needed to 'chisel' at it from above with the head off, which knocked out lumps of casting sand. It can stay, it's not doing any harm, it's at the bottom where the engine is much cooler anyway.
paulh4

I'm an avid rad and block "back flusher"!
But be prepared for your rad to leak on re-fitting.
Some of the "crud" is sometimes sealing small leaks and the "crud" is often the result of an application of BarrsLeaks, or something similar. Seldom egg or mustard these days!!!!!😂
Allan Reeling

I do all my drains as warm or hot as I safely can, coolant, engine, gearbox and rear axle, this brings out more oil and muck in the draining.

If poking around with a bit of stiff wire loosens anything and it comes out it's got to be good, for a start the clearer the engine block drain hole is the more fluid and crud you're likely to get out from it and potentially less residue of liquids and crud and build up of those behind any partial blockage there.

The rad and heater matrix are devils to get fully decruded and the rad holds on to some residue liquid despite lots of efforts to fully empty it. So Mike starting with a new fully clean (inside and out) rad can make a noticable difference by itself.

Nigel Atkins

A pal had his cross-flow rad bunged up by Barr's Leaks. He took it to a specialist, they unsoldered one end tank and rodded out all the slots which were sludged up. Obviously the product is so good it stops coolant 'leaking' through the radiator tubes ...

I had a pin-hole develop in a Mini rad with a small jet coming out, poured in some Radweld, the jet slowed and stopped and I had no more problems. I've been carrying a small can on long-distance trips for over 30 years, perhaps time I replaced it.
paulh4

Paul, your Radweld has probably sealed up the hole which lets it out of the tin by now!😁
Allan Reeling

Ah yes :o)
paulh4

So if your pal's x-flow rad was really sludged up by the use of Bars Leak why would you carry and trust Radweld.

"Why trust one drug and not the other" - Danny.

"If they {radiator specialists} told you wolverines would make good house pets, would you believe them?" - Del.

"It was the sandwich I eat and not the gallon of Abbott that made me ill." - a pal's beer specialist.
Nigel Atkins

Oh Nigel you are such a cad.
paulh4

Sorry, that should read 'card' ...
paulh4

I have been very pleased with my Revotec. My car doesn’t like traffic even after a flush and the Moss shroud was fitted, it did help.
All my fault as the engine is bored out and tuned. I found the Revotec difficult to set up, it tended to get twisted and bind I had to spend a long time experimenting with combinations of washers under the mounting points.
I was replacing a metal 3 blade fan so not a hard act to fo.
Stan Best

Willy

Good point, I may give the 7 blade a go. If it really annoys me I think I can change it back without removing the rad?

Mike Dixon

77 and later it's easy of course. Before that it's possible depending on the size of your hands. If you just remove the bolts holding the rad to the diaphragm and tilt it forwards you should be able to get a bit more space. Can't guarantee as I've not needed to do that.
paulh4

Just a point concerning overheating!!!

The gauges are not that accurate, and best used to judge deviation from the norm, and I don't mean the "N".
If you have, or have use of, an Infra Red thermometer. Compare it's reading with your gauge...............you will be surprised!
Allan Reeling

I agree, but on these cars they frequently 'deviate' as conditions vary which is why people get paranoid about them, comparing them with modern cars.
paulh4

Allen
There is also an issue with hand held infra red thermometers, you can't rely on the reading 100%
The shinier the surface is the more the reading will be out of whack--as with a polished aluminium radiator, it's difficult to get a reading and say a nice shiney new t/stat housing plays up with them as well
Cheers
willy
William Revit

Emissivity.

David Billington told me about this a couple of times, but I still had to look in the Archives to find the word as I could remember it.
Nigel Atkins

Nigel--I'm impressed that you could remember that you couldn't remember
William Revit

Willy.
Spot on, did you do a Leslies Cube experiment in your physics lessons??
The lighter colour and more polished the surface the LESS heat it radiates.
Conversely a matt black surface is the most efficient radiator.
Hence pick a spot on the head near the temp transmitter, the top of a painted brass rad, even the top hose, when engine is up to temp and do a bit of averaging in your head.
Allan Reeling

It also depends on how large the emitting surface is and how close you are. The laser dot means nothing, most of them sense using a cone so for something like the thermostat housing you have to be right on it or it averages it with the surrounding area. Some are a 2:1 cone, others are 1:1 and almost useless.
paulh4

Willy,
yes I also often forget to include the word not, usually I notice but often I don't.
Nigel Atkins

I noticed but just thought maybe you had forgotten to remember it or had'nt noticed that you didn't notice it, well not it but not----lol
William Revit

I don't not normally noticed but often I do, which can making things even more confusing than what they are already or can become, that's without mixing up opposites, but the errors never cancel themselves out, unless they do and I don't notice of course.

I like to keep things simple. 😁

P.S. I had noticed your had'nt. 😉

All ties in with the inaccuracies of using accurate tools and the reliance on one action taken without reference or cross checks, all serious stuff.
Nigel Atkins

Nigel, let's not confuse accuracy with precision. Those infrared temp guns have great precision (double decimal place degrees) with +/- sometimes several degrees of accuracy. A slide rule is accurate with lousy precision; a digital speedometer is precise with sometimes lousy accuracy. They're not the same.

Courtesy of my old favorite ChemE professor.

Jud
J K Chapin

Jud,
thanks, I remember you putting this before but couldn't remember which way round it was. How's this -
All ties in with the inaccuracies of using { precision } tools, and the reliance on one action taken without reference or cross check.
Nigel Atkins

Couldn't say it better. Sorry for repeating myself. I didn't remember that I had but that a different discussion :-)
J K Chapin

Jud,
you didn't repeat yourself as such because I saw it in another thread a while back, and it's certainly worth repeating.

I wish I could say I'll get it right next time but I have a habit of reverse memory, I remember the opposite.
Nigel Atkins

This thread was discussed between 23/02/2021 and 01/03/2021

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