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MG MGF Technical - engine bay fan switch

Sorry if this an old and tired subject, but is it possible to activate the engine bay fan manually?
My chain of thinking started with 'the quest' to find a suitable airbox to fit over my K&N. I was impressed by Rob Bells ideas - but have been spectacularly unsuccessful in finding either an old Rover 820 airbox or suitable ducting pipe. I'm sure many others have had this problem! I then started to think about the engine bay temp problem in general, i really would like my k&n to be sucking in cooler air - even when stationary. It wouldn't do any harm for the rest of the engine components, and may (yes I know about the debate) reduce HGF. I figured that a manual switch to the fan would do the trick - or even better, the temp sensor could be changed to come on at a lower temp, say 40 deg? (Is the temp sensor controlled by mems and hence needs reprogramming, or would it need a replacement sensor?) So many questions! Thoughts please!
P.J. Shuttleworth

>Sorry if this an old and tired subject,

Recieved the apology ;)
It is of course not only tired but dead, if an engineer reads the idea of cooling 60kilo+++ Aluminum, Oil and water with a breath of air. ;)
Cold air with better load of oxygen to the airfilter is another case.

Anyway, the Sensor is a PTC, mounted above the expansion tank. Controls MEMS and the relay for the small 'farth thingy' is the yellow one in the front bonnet.

Good luck
;)
Dieter
Dieter Koennecke

Dieter - you misunderstand me, I'm not looking to cool the engine, just the air surrounding it to help the air intake temp.
Phil

LOL, me only tried to keeping others off from 'the old story'.
No worries, please.

A german guy recently mounted a independent 'pipe fan' dia 80mm to the air induction hose of his K&N. Always on with ignition on. I think DIY reworked from any old computer power supply assy ;)

Though, should be a fan with a huge air pressure to see any effect, IMO.

Cheers
Dieter

Dieter Koennecke

Dieter

Like a 'supercharger' for instance!

Ted
Ted Newman

Or nitrous injection ;)
Wrrroooaaam !!
Dieter Koennecke

>>> or even better, the temp sensor could be changed to come on at a lower temp, say 40 deg?

And what about parking the car in the sun after returning from a good drive. Fan will keep running for some hours, untill the temperature drops below 40C again.

Or is time conrtolled after turning the key ?

just a thought.
Erik

>>Or is time conrtolled after turning the key ?<<
maximum of 8 minutes IIRC.

You could get it to come on at a different temperature by wiring a suitable resistor across the sensor (the sensor is just a temperature sensitive resistor). You could experiment with a 4.7Kohm preset. Alternatively, you could just find a different sensor (the mounting is not too important in this case).

A standard pot will plug in directly to the wiring loom if you wish to experiment.

Steve
Steve

P.J.

Just in case you still haven't found any thing in the archive, you can buy 100mm Ali ducting from Wickes and B&Q. It's proper purpose is ducting for cooker hoods, so it is heat proof and very flexible. The only problem is that the corrugations possibly disrupt air flow to some extent, but it fits in the same space as the Kinnor twin pipe arrangment. If you want to go a stage further, get yourself a 200mm flower pot with lid as a surround. Not so professional as the Rover model, but works just as well.

Chris
Chris

Hi Phil,

Chris' suggestion regarding the flower pot mod is certainly a good route to take, and has been used to good effect in a number of Lotus Elises! Doesn't cost too much- but isn't much to look at sadly (but hey, it is not an area that gets seen very often in an F!!!)

The flower pot mod is a preferable route to obtain more power via cold air than altering the thermostatic cut off for the engine bay fan (but I like your lateral thinking!). Two reasons for suggesting this:
1. The fan doesn't shift enough air. The engine is a recirpocating air pump. Assuming 100% efficiency at 3000 rpm in a 1.8 litre engine, with air being sucked into one cylinder with every engine revolution, then the engine is consuming 450 ml x 3000 rpm = 1350 litres of air every minute... (22.5 litres every SECOND). Obviously, the engine air pump is nothing like 100% efficient - may be 25 ish %??? but you are still looking at nearly 6 litres of air per second. That's 6000 cm3. Or 0.006 m3. So the engine will suck in the volume equivalent of the engine bay within 30 seconds. The fan simply would not be man enough to cope with that kind of demand. Then there is the question of the heat being radiated into the engine bay... more maths, but the story is essentially the same - the fan is inadequate to drop the ambient temperature in the engine bay to anywhere close to the ambient temperature outside the car.

2. The location of the fan: it's on the opposide side of the engine to the air filter, so any air being sucked in will have to pass over the exhaust manifold...

So basically, an interesting thought on how to deal with a very real problem, but sadly, the standard fit fan is not the way to go.
Rob Bell

Thanks people, I invited comments and thats what I've got! I've admitted in other threads that I'm not an engineer and appreciate more experienced views.
Chris - yes I've tried all local DIY places without much success. I feel that ducting is only a part solution because of its open ends, some hot air still gets in. Even though the engine bay is out of sight and people have reported success with flowerpots, I'd still like something more professional. I'd also worry about it melting! (Why don't I just go out and buy a ptp or hurricane then? - because I'm a tightwad! and an average overtaxed British motorist!)
Rob - you make it sound like the fan alone provides the air going into the engine bay - You and I know this isn't true. The fan would complement the effect of k&n pipes and normal effect of forward motion. I wouldn't expect ambient temperatures to be perfectly equalised and still feel for the relative ease of keeping the fan going, the benefits outway the disadvantages.
Phil

Hi Phil,

the technical BBS is always a great place to sound out ideas - not least because sometimes the wackiest ideas actually work out when tweaked by other people's suggestions.

Okay, back to that fan. Yes, I completely agree - the fan is certainly not the only route of cooling air into the engine bay when the car is moving. In fact, I'd go a stage further with that comment: it is a *minority* source of air when the car is moving.
Moreover, when the car is moving, the K&N cooling ducts do a good job of dropping the temperature around the air filter - from 70+ stationary to under 40C when at a cruise (Graeme Bishko's figures). The contribution that could be made by the engine bay fan at speed is likely, therefore, to be vanishingly small.

The biggest disadvantage of the K&N 57i system is when the car is at a standstill - as you quite rightly point out - and this is the scenario that I was more alluding to where the fan is more likely to be making a contribution to reducing the ambient engine bay air temperature. The thing is, to emphasise point (2) above, the engine bay fan is located on the bottom of the right side of the engine bay, forwards the front of the car whilst the air filter is located at the furthest point from here - top left hand side of the engine bay, towards the rear of the car. Therefore there is a large block of rather hot metal sitting between the fan and the filter - an effective wind break that'll also warm the air flowing around it most effectively.

Unfortunately, altering the trigger temperature for the fan really isn't going to alter these facts :o(

A better solution might be to locate a fan in closer proximity to the filter - but this adds weight and complication. Better would be to attempt to isolate the filter from the hot engine bay -- a heat shield works surprisingly well on a cruise, but better would be an airbox of some description that would also work when the car is stationary. This is why I've been working with the Rover 820EFi air box, but anything similar would work too (the 2.0litre Maestro and Montego use a similar, but longer airbox that could be made to fit...)

The KIS (Keep it simple) principle works best for me ;o)
Rob Bell

I don't want this to be forgotten in this interesting thread:
the engine fan is blowing the hot air out of the engine bay, instead of blowing fresh one into the bay.

It's a detail ;-)

Erik

No Erik; it is sucking air into the side shaft and blowing it into the engine bay and it then exits from the top grill - if yours is doing it the other way I should get your dealer to check it out:-)

Ted
Ted Newman

Wohow... I think I need to check my car.
Found it a bit strange, but... I really thought he was blowing the air out of the bay.
Erik

Erik

If you hold your hand by the grill of the right hand side inlet when the engine bay fan is running it feels cold around the fingers IF it was blowing out it would feel warm OR try the smoke test - hold a smoke cannister (or Belgium Cigarette:-)) by the grill when the fan is running and observe where the smoke goes.

Ted
Ted Newman

Thanks Rob, as ever your views are appreciated. What you say is probably true; I started my chain of thought whilst looking at the simplest solution! I kind of hoped that a simple wiring exercise (as simple as lighting the cigarette lighter!) could improve things whilst we all try and find a suitable airbox mod!
Phil

> hold a smoke cannister (or Belgium Cigarette:-)) by the grill when the fan is running and observe where the smoke goes.

Ted,
don't make him a smoker. ;)

A piece of paper held in front of the grill and then release gives much better evidence.

Dieter
Dieter Koennecke

Hey guys,

come on, I am not that technical, but I know how to determine if the fan is blowing or sucking the air ;-)

cheers
Erik

No worries Phil. As I say, I think that your thought processes are spot on, and as you say, altering the fan cut-in temperature would be a pretty simple fix. It's just that the fan simply would not be effective in achieving the aims you have set out.

Good luck with the airbox/ enclosure. Still haven't fitted mine - only one more bit to source -- and ofcourse I need some spare time! ;o)
Rob Bell

This thread was discussed between 06/07/2002 and 10/07/2002

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