At 01:27 PM 8/30/97 -0700, you wrote:
>Tom,
>
>Thanks for your input on this subject. A quick questions however: Several
>months ago you suggested that I move the radiator cap on my Tiger.
>Frankly, I did not understand this suggestion as my Mk-1 has a copper
>"header" tank that has the cap on it rather than on the radiator itself.
>Through trial and error, I have discovered that it is best to keep the
>header tank no more than half-full. In addition, It should be noted that
>the header tank is mounted on the fender well, well above the top of the
>radiator. Am I missing something or is everything after the Mk-1
>different. Sorry to ask the question but I just do not have enough
>experience with Tigers yet. Plenty with small block Fords and other LBC
>though!!
The cooling system is dynamic and has different pressures in various
locations. The system was designed with various fixed orifice holes to
control distribution, and one variable (the thermostat) to control
temperature. The water pump impeller is the lowest pressure area in the
system, and if it is turned too fast or poorly designed impellers designs
are used, cavitation (the formation of steam bubbles) occurs. The inlet
side of the pump and the tank it's connected to are the next lowest
pressure areas. The pressure cap only "sees" the local pressure, so the
pump inlet tank is the proper location for this device. By relocating the
cap to the top of the inlet tank, the cap relief pressure is effectively
increased by the pressure drop through the radiator core.
The original header tank should never be over 1/2 full or expansion will
quickly reduce it to that level. You could simply re plumb the header tank
to the right hand side of the radiator, but the plumbing would be awkward.
Most of the "relocations" I have done or seen, use a non pressurized
expansion tank, just like most late model cars do. This will keep your
system fuller and make it more effective.
The restrictions of air flow are a major problem for Tigers. At low
speeds, air recirculation around the radiator reduces its effectiveness.
At high speeds, inadequate air flow paths restrict air throughput. The two
holes on either side of the radiator are major culprits. All air entering
the engine compartment from the front should be forced to pass through the
radiator. Full shrouds and electric fans can help at low speeds. At high
speeds, you have to get the air "out" once its through the radiator.
That's why you see so many cars with supplemental vents such as LAT hoods.
A front end air dam is also effective to reduce the pressure under the car
to aid hot air flow as well as adding high speed stability.
Tom Hall
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