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Mikell

To suck - or to blow ?

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Ok, this may be silly question time, but here goes ...... :huh: ..... Several years ago I had a manually switched pacet fan installed to the 4a, whilst also retaining the fully functioning original fan. I wanted extra fanpower as although the engine had only done about 10k miles as a professionally fully rebuilt unit it tended to go too close to the red for my liking on really hot days in static or crawler traffic. The fan performance never greatly inspired me, as it didn't seem to make a great deal of difference to gauge temperature when I opted to switch it on - so I thought hey never mind, it was worth a try. Now, whilst cleaning the engine bay this morning I dropped my polishy cloth whilst the pacet (only) was running, and noticed said polishy cloth clinging for dear life to the engine side of the rad. This means then that the pacet is set to suck hot air out from the engine bay through the rad and out of the grille .......and hence the silly question - is that right, or should it be operating the other way and pushing outside cool air through the rad and into the engine bay ?

Opinions very welcome, and if the question is really very silly indeed - then please be gentle with any responses !!

Cheers, :)

Mikell.

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Mike,

 

Your fan should be mounted on the engine side of the rad, sucking air through the rad. I would imagine that this is impossible with the original fan in place. Some fans can be reversed, but I think the Pacet is not! If you can find the part No. of the fan, you could contact Pacet to find out if it can be reversed.

 

http://www.pacet.co.uk/

 

On my TR4A, I have a Pacet 16" sucker fan on the engine side without the original fan and it keeps the temp between 1/2 and 3/4 on the temp gauge scale.

 

Cheers

 

Graeme

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Hi Mike,

thank you - I feel so wonderfully normal now. B)

 

Clearly the fan in sucking forwards, instead of pushing rearwards, was also stopping the engine fan from working. :blink:

 

If you remove the engine fan and install the Pacet on the back face of the rad it will do all you require.

 

Otherwise - simply connect the fan in the reverse of what it is at present. If it rotates the other way then leave it in place as a pusher.

 

However sucking is better than blowing - more efficient.

 

Or you could (more difficult) mount the Pacet in front of the rad but turned around to act as a pusher - however very inefficient.

 

Roger

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This means then that the pacet is set to suck hot air out from the engine bay through the rad and

out of the grille .......and hence the silly question - is that right, or should it be operating

the other way and pushing outside cool air through the rad and into the engine bay ?

 

 

Errr . . . . senior moment, I think.

At least it hasn't done any damage and it shouldn't be difficult

(or expensive) to rectify.

 

My feeling would be that, in operation, blowing would be slightly

more efficient that sucking but in normal use, it would be better

to give air flow unrestricted flow to the rad.

Overall, better to suck than to blow.

 

AlanR

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Hi Mike,

I agree, the most efficient place for the fan is on the engine side sucking, but top efficiency is only achieved if a suitable cowl is used which covers the full width of the Rad and as much of the height as possible. On vehicles which run at slow speeds like Tractors (which I worked with for 30 years) the cowls are sealed with foam/rubber strips where they meet the Rad; this creates a venturi effect which increases the airflow and at higher speeds the load is taken off the fan motor and current draw reduces. :D

On my 4A I have a fan and cowl from a Fiesta XR2 which was selected because the cowl is the same width as a TR Rad, it's been on the car over 10 years now and only comes on when in slow moving or stationary traffic after fast running.

 

Chris

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Guest ntc

First of all making the fan run backwards will not work. A pusher fan is better if correctly shrouded, ask yourself all modern cars are like this

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First of all making the fan run backwards will not work. A pusher fan is better if correctly shrouded, ask yourself all modern cars are like this

 

 

Very good point, now I feel better having baught a pusher fan :)

 

Is it better to mount the pusher fan at the top or the bottom of the radiator? I remember some discussion on this a while back, and also reading something in the Williams book, but cant work out the logic.

 

Cheers,

 

Richard.

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Personally I don't think the total resistance to the air flow is much altered whether it goes through the fan first or the rad.

Which ever way round you do it, the fan has to be "sealed" to the radiator. Otherwise the fan output (blown) or input (sucked) will take the easiest route which is not through the rad.

FWIW: My fan is a blower to give a clear area in front of engine and control is from a sensor mounted in the metal down pipe. I have an underdash mounted over-ride switch but after the first few weeks I forgot all about it and have had no over heating problems.

 

 

Mike

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Thanks Mike, this is the installation that I had also planned. (I found an old stag fan switch to work as the manual overide, and it nicely fills an empty hole on the center arch.

 

As I understand it, (from other threads on the forum) the part of the radiator which has the greatest exposure to relative airflow when the car is moving is the bottom.

 

I was intending to fit the fan at the top of the rad for 4 reasons:

 

1. Heat rises so I assume that the top of the rad would benefit most from the additional cooling when in slow traffic

2. The fan will obscure less of the natural airflow which strikes the bottom of the rad during normal driving.

3. The fan will be out of the way of water and debris which should help it live longer.

4. it will be less visable higher up. (As much as I like the idea of improving the car, I dont like to see plastic)

 

Does all of this add up? Or have I missed something?

 

Cheers,

 

Richard.

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Thanks Mike, this is the installation that I had also planned. (I found an old stag fan switch to work as the manual overide, and it nicely fills an empty hole on the center arch.

 

As I understand it, (from other threads on the forum) the part of the radiator which has the greatest exposure to relative airflow when the car is moving is the bottom.

 

I was intending to fit the fan at the top of the rad for 4 reasons:

 

1. Heat rises so I assume that the top of the rad would benefit most from the additional cooling when in slow traffic

2. The fan will obscure less of the natural airflow which strikes the bottom of the rad during normal driving.

3. The fan will be out of the way of water and debris which should help it live longer.

4. it will be less visable higher up. (As much as I like the idea of improving the car, I dont like to see plastic)

 

Does all of this add up? Or have I missed something?

 

Cheers,

 

Richard.

 

 

Richard

 

I think you have it, Mike's comment is vital, you need lamination as the final ingredient. All modern fans now work flush to the rad with a rim or cowling, reducing fan tip spillage and ensuring it all goes the rad. That, and a well fitted cowling on the other side of the rad, which will funnel free air into the rad reducing the need for the fan to switch on whilst raising the threshold where it does cut in. Sortedlaugh.gif

 

MMmm, if all this works why did they dump the rad cowling for the TR5 blink.gif (its never easy is it)

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Well yes heat does rise, but this is a dynamic situation where the water is pumped thorugh the rad, so wherever the fan is it will be cooled as it passes through. FWIW: my fan is at the top on visibility grounds, and I plan one day to fit a small oil cooler. As I don't have precision metal working skills, I stuck two pieces of duct tape together and then taped that to the fan cowling. This gives a non damaging contact seal and painted matt black it looks a 'proper job'.

 

 

 

Mike

Edited by MikeF

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I was about to come up with a semantic explanation about the differences between colloquial english and american. Then I figured better.

I am actually in the midst of such an installation. The previous engine had a mech fan and a 10" Kenlowe fan of the blowing persuasion. Roughly OK if not for a complicated plastic grille right in front of the prop, hence a rather timid blowing effect.

 

The new engine has a harmonic damper and no blades. Overheating was immediate in traffic.

So I installed a 12" sucking Kenlowe (Alec P., I don't wanna hear about this).

12" is the perfect size, coming flat against the rad sides. It uses the Moss side tube and probe combo and works OK. No plastic grille here and I took great care to apply the fan as tight as possible on the rad. The manual override is a must and takes constant juice from the fuse box. Quite happy with the result, even in worst traffic jams.

The rad cowl is basically a support for the electrical loom and I did not bother with it except reinforcing the screw holes with metal eyelets.

 

I also have an oil rad, dunno If I really need it but it's been here for ages and at least I get some extra oil.

 

BTW, now that I have an harmonic damper installed, I have a discrete vibration at 2500 rpm which was at 3700 rpm in the classic engine. Any comments?

 

Badfrog, cooled as they come....

Edited by Badfrog

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"So I installed a 12" sucking Kenlowe (Alec P., I don't wanna hear about this)."

 

Blimey Badfrog, Lady Ann leaves Linda L standing . . . . ;)

 

Cheers,

 

Alec

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Hi all, and many thanks for the various sucking and blowing comments and advice...... :P ..... I've now dropped the 4a into Classic Marques, and they've reversed the direction of the fan while I waited - took all of 3 or 4 minutes - and hey presto it's now working in the same direction as the existing mechanical fan. I have no idea what model number the fan is, but it changed direction "just like that" and it seems the Pacet range may be kindly disposed to such reversals. So once again those excellent Classic Marques guys have sorted things for this owner of limited capability !!

 

All I need now is some good hot weather to see if the reversal keeps the static guage temp away from the red - fingers crossed on both counts.

 

Cheers,

 

Mikell.

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Having read this topic completely, it brings back memories...

 

First, I have a Pacet fan (type 1111) behind the rad. I choose for the Pacet when I compared the specs. of the Pacet and the Kenlowe. At that time, the Pacet was stronger, displaced more air and took less current when starting and running, compared with the Kenlowes that were on the market 3 years ago. Perhaps things have changed, since then.

 

I found out, that a fan behind or in front of the rad. has a beneficial option: when the fan doesn't run, the blades will turn when the car moves: the air coming through the grille will set the blades in motion, thus forcing air through the rad (or sucking air through the rad. when the fan is mounted behind the rad. I had some concerns putting a fan against the rad., blocking the free passage of air. But now, after a Summer of motoring, I don't worry anymore about the place: in front or behind the rad. If you put a fan in front, you'll be able to maintain the original set up (wide pully, original fan etc).

 

I ditched the control knob under the bonnet. I only have a thermostat mounted into the downpipe, like most of us have. And then there's the partial blocking of the bypass. But, I'm sure you already know all about that.

 

There's an old TR3A knob on the dash, with a period control light mounted above (the light is from my dad's old 1965 Austin Glider!). The switch acts as an override switch and the control light comes on every time the fan cuts in. And that's a good thing! On my first test drive after restoring my car, the needle of the temp. gauge kept on rising; the fan didn't cut in... (and the light stayed out). After some careful thinking, I found out that the brand new (!!!) Bosch (!!!) relay had an internal fault! When I replaced the relay, all went back to normal.

 

Menno

 

The knob on the dash: next to the OD switch. From bottom to the top: w/washer pusher, heater rheostat and on top the pull switch with the period control lamp

 

P1040040.jpg

 

Here's a pic of the Pacet. Not attached with straps through the rad. core, but with welded brackets.

P1020272.jpg

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