[Mgs] Best Electric Cooling Fan for MGA

[Barney Gaylord]

This is getting a bit away from the subject line, but following the discussion.

At 12:34 PM 6/21/2007 -0400, WSpohn4 at aol.com wrote:
>....
>I highly recommend that people have their filler neck replaced at 
>the time they recore the rad so that they can run more than a 7 lb. 
>cap. Using a 15 lb. cap allows you a wider margin.

How hot do you intend to run the cooling system?  50/50 mix of 
glycol/water boils at 223dF at sea level.  Boiling temperature 
increases about 3dF for each psi of applied pressure, so the 7psi 
pressure cap takes the boillong point up to about 244dF.

My MGA temperature gauge goes up to 230dF.  It is verified correct at 
212dF with the sensor in boiling water.  Last weekend I managed to 
drive the coolant temperature up to near the 230dF mark with extended 
puttering around a few small towns during a club rally (with 90dF+ 
ambient temperature).  When I shut the engine off the indicated 
temperature would go higher, in fact peaking out at 85 PSI in the oil 
pressure scale on the combination gauge.  That would be at least 
240dF, and still it didn't boil or dribble.

The only thing to be gained by increasing the pressure rating of the 
radiator cap above 7psi is the capability to drive the cooling system 
temperature even higher than 244dF without boiling (233dF with plain 
water).  Such higher operating temperature is far beyond the end of 
the gauge scale reading, so you would have no indication of the real 
temperature until it might start to boil and spit.  If you have any 
intention of going into that operating range you will need a 
different temperature gauge.

As noted by several others, as long as it doesn't boil the engine is 
safe (if not entirely happy).  The greater problem these days with 
our carbureted vintage cars is boiling of fuel in the carburetor, 
which is aggrevated by the presence of alcohol in the fuel.  This is 
not a problem during cruising at road speed when air intake and fuel 
flow is sufficient to cool the carbs.  But puttering around near idle 
with slow ground speed on a hot day allows greater heating of the 
carbs.  Under those conditions my MGA has problems with vapor bubbles 
in the fuel causing a lean running condition (at anything over 
220dF).  In this case I have to pull the choke out to keep it running.

As such, I cannot imagine wanting to run the cooling system hotter 
than 240dF, so no reason to use a pressure cap higher than 7psi.

>....
>.... I like a 15 lb. cap.  I use a 25 lb. cap on the Jamaican.

Wow.  15 psi brings the boiling point up to 268dF (with 50/50 
glycol/water).  25 psi is more like 298dF.  I know some new cars with 
fuel injection and fuel recirculation systems may run into that 
range, but for our vintage carbureted MGs the higher pressure cap 
only puts more pressure stress on the radiator structure (apt to 
burst a solder seam).  Due to thermal expansion of the coolant, as 
soon as the system starts to warm up it starts to expell fluid past 
the pressure cap, and system pressure rises immediately to the relief 
pressure rating of the cap (even when coolant temperature is well 
below the boiling point at atmospheric pressure).

>As an alternative, I have machined up a thin aluminum ring that can 
>be epoxied into the neck. It has to be the correct thickness to take 
>a shallow neck cap and it has to have a hole in the centra that 
>doesn't foul the little valve in the cap, but it isn't exactly 
>rocket science. ....

Years ago my similar solution was to drop in the 1/4-inch thick 
rubber seal ring that is included with the cooling system pressure 
tester.  I did it because I was installing a coolant recover setup, 
and the long neck caps were not available in recovery style with the 
top rubber seal.  That worked fine for a few years, until I had the 
shorter neck installed on the radiator.  These days you can buy the 
long neck cap in recovery style (up to 7psi).

Barney Gaylord
1958 MGA with an attitude
http://MGAguru.com