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MG MGB Technical - 77GTV8 Thermo Fan(s)

I am endeavouring to work out the best way of cooling my 3.5L V8 - the options being;
1. Two fans on engine side (sucking) each drawing 5.0 amps and moving up to 424cfm - 848cfm total. The total area covered by the two fans is 628 sqcms or
2. One fan on the front of the radiator (pushing) drawing 7 amps and moving up to 847cfm. The area covered by the single fan is 572 sqcms.
I understand that the preferred method is to have the cool air being pulled through the radiator core.
The reason for the two fans in the first option is that I do not have sufficient clearance between the water pump pulley and the radiator to fit a single fan.
Obviously it would be more cost effective to go with the single fan if it would be up to the job.
I would appreciate your advice and any other related details.
Thanks
Peter M (Member)
Peter M (Member)

how about a single offset fan with a shroud?Ric
RIC LLOYD

Puller fans are definitely more effective, especially with a shroud, if you have the space. The RV8 had a single very low profile shrouded unit which virtually went top to bottom and side to side of the rad, and its cooling was incredibly stable unlike the twin small pushers with no shroud on the earlier V8 and export 4-cylinder cars. A huge amount of the air moved by those pushers is simply flung off the tips and 'lost'.

The larger surface area is also more effective, as it reduces the surface area that is left that coolant can pass through *without* being force-cooled, i.e. not cooled at all at a standstill.

Radiator design is also a factor, i.e. cross-flow or not and whether the inlet and outlet are diagonal on on the same side. One assumes cross-flow is more efficient given its pretty-well universal use these days, but that may just be ergonomics and its lower vertical profile enabling lower bonnet lines. Diagonal is also more efficient as the coolant is more likely to flow through all the tubes instead of the majority flowing down the tubes closest to the inlet and outlet, which reduces effective surface area.

628cm equates to about 25x25 cm or 10 inches square, which is pretty big on a standard radiator, 572 to about 24x24 which isn't much less. Single large fans are more effective than twin smaller ones as there is double the ineffective space in the middle of the latter. If the single pusher has an effective shroud then I wouldn't think you would be losing much, but at quite a bit less current and cost, one presumes.
Paul Hunt

Peter,

on my V8 i am running two 10" pullers behind the rad. They came from the Mini Innocenty L90/L120 in the late 70's and work fine since the early 80's in my V8. They are srouded and i bult a ram air box in front of the radiator so temperatures are allways between 80 and 93°C.
Once i had troubles with one of the fans and canged to a single shrouded Bosch puller from a Renault 19 Turbo. It also worked well but i changed back soon after repairing the defective e-motor of one of these fans, as there were issues with a propper mechanical installation of this 'large' fan, tending to tumble when working on speeds.

Ralph
Ralph

Thanks all for replies. Will go for largest pusher that I can fit.
Peter M
Peter M

Peter,if you offset a puller you should be able to fit it, with the correct shroud it will be the best deal all around.Much better then any pusher system you might come up with, when all things are considered. Ric
RIC LLOYD

Ric
Thanks Ric - I'm unable to just have one puller as even at the circumference of the Davies Craig unit the clearance between the water pump pulley and the radiator won't allow it hence my thoughts as to two pullers.
I will opt for Paul's suggestion with the largest pusher and shroud.
Peter M
Peter M

Peter - the factory twin fan setup will do the job in ambients up to 105F but the blades need to be close to the rad and the motors and wiring need to be in good working order.

The advantage of a twin fan setup is that you still have one when the other fails. A single fan will keep a 3.9 steady on a warm Summer day.

modern ally motors are very vulnerable when their single fans pack up - as I found out with a Volvo.

FWIW Roger
roger

I would simply change the radiator. An alununum 4 core radiator would provide more surface area for cooling and the aluninum dissipates the heat much quicker. A fan would also help.
S.L. LaPaugh

Hi SL
I do also have a new aluminium radiator so shouldn't have any problems.
Thanks
Peter M
Peter M

This thread was discussed between 27/01/2009 and 03/02/2009

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