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MG MGA - Blower for Under Bonnet(hood) cooling

Lindsay Sampford....I have just read Barneys comments ( CB-208) on your blower installation to blow cool air into carburettor location and it looks a great method. ...I am keen to locate a 3in Attwood fan ( $20 on Amazon ) in the circular steel duct outboard of the radiator to blow cool air down past the air intake filter.
..Is the fan rated for continuous use?
..Does it need a relay ?
...I may hook it up with a thermo switch so that it comes on when the under bonnet space gets too warm..any temp suggestion for setting? or should I just have it come on when my electric radiator cooling fans kick in as this may be the hottest time...a real banshee of fans!
...Is it noisy at speed ? at idle?
Neil Ferguson

I can answer most of those questions. The 3" fan will be quieter than the 4" fan. It will be even quieter yet inside of the air duct. It does not draw much current, so it does not need a relay. It is designed for continuous running.

Connecting it to come on with your electric radiator fan is probably a good idea. The carburetors only suffer from heat when engine bay temperature is very high, which means your electric radiator fan will likely be running at that time. If you connect it in parallel with your rad-fan, check to be sure you are not overloading the thermal switch or relay that controls the rad-fan.

If you connect the carburetor blower fan on a separate thermal switch, you might attach the temperature sensor to the front carburetor float bowl. The front carburetor runs hotter when the car is moving at moderate road speed (above 25 mph), as cooling air enters the cowl vent to blow on the rear carburetor. The carburetor heat problem is caused by hot fuel (boiling alcohol), so the float chamber seems to be the best place to monitor the fuel temperature.
Barney Gaylord

Neil, have you checked out the "More on vapour lock" thread in the archive?
It has lots on the subject and includes Lyndsay's report on the 4inch bilge blower that he fitted into the carbs air supply hose.

I heard the bilge blower running on his car at last augusts MGA day and whilst it has a mildly hoover like sound to it, it really does deliver a lot of cool air over the carbs.

It seems to have solved Lyndsay's vapour lock issues though.

Any further updates Lyndsay?

Colyn Firth

Colin/Barney ..thanks for all the quick and comprehensive advice. I have now read the archives and based on all the bumf I consider I will do the following...............
When I wrote the post I was considering primarily getting cooler air to the air inlets to the carbs. .I have not suffered the carb. boiling problem. Cool air sucked into the cylinders obviously means more molecules more umph. I believe that probably this means keeping the fan on continuously . I intend to build an heat shield/shroud between the exhausts and carbs/filters and underneath as well so that the air blown in is preferentially directed past the carb assembly i.e. essentially an air box . I am keen enough so have bought the 3in fan on amazon ( $28 incl transport to!) and it should be totally hidden inside the duct when I cut the mounting feet off. I intend to just use simple door draught rim excluder strips tp make up the outside did from 3 to 4 in.. to get the fan to fit snugly inside the duct . I don't think I need the upstream duct to the front of the car as the fan should ensure I pull cool air from the plenum in front of radiator. Appreciate any comments......especially on last point.
Neil Ferguson

I have also bought a sheet of this material to use for the heat shield.
Neil Ferguson


I have attached some photos of our heat sheild from the same material. Some of the excess material was fitted to the back side of the original shield as per the original asbestos.

David Lake was your pics and comments that inspired me to buy a sheet of the material. Is there any advice you can pass on re. Cutting, shaping and supporting the stuff?
Neil Ferguson

This thread was discussed between 18/03/2012 and 22/03/2012

MG MGA index

This thread is from the archive. The Live MG MGA BBS is active now.