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| Joined: | 03-12-2005 |
| Location: | Kingman, Arizona USA |
| Posts: | 532 |
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Quoting Tim Engel from something he wrote years ago:
[ ...] In the turbo engines and later 912's that use the uprated turbo water pump, the frost plug is replaced with a pressed in nipple. A 3/4 inch 90 degree molded hose then connects it to a second water inlet to the turbo pump. This provides another return flow path back to the water pump in addition to the one through the intake manifold water passage and cools the head better. [ ...] If everything else was fine, the turbo pump would provide a little extra cooling for a safety margin on hot days.
It's my understanding that moving the heater takeoff spigot from the middle to the rear of the head will increase the coolant flow through the rear of the engine, provided the heater shutoff valve, if present, is open -- but has no effect if this valve is closed. This being so, a first step would be to remove the shutoff valve Note that the heater core would not be of any use as a supplementary radiator unless air were flowing through it, which in turn would mean that the cockpit would end up very hot in summer. This is unlikely to be desirable.
I think you'd be better served by using a larger radiator than by trying to use the additonal spigots on the turbo pump in conjunction with a heater core to provide supplementary cooling. However, the turbo pump, with the spigots replaced by freeze plugs, apparently does provide better cooling than the earlier pumps -- my car has no overheating problems in street driving even at ambient temps above 100^F, and it has some sort of post-JH water pump installed (though I'm not sure which one as I can't see the casting number).
When next your water pump is removed, you may wish to examine the rectangular hole at the rear of the water pump cavity, through which coolant flows into the block. These holes are very small, and the factory typically opened them up quite roughly with a chisel, so they offer a huge restriction to coolant flow. Even a very small amount of 'porting' with a die grinder or a file should improve things tremendously.
Finally, regardless of version, water pump performance depends enormously on the clearance between the impeller vanes and the tapered region of the pump casting. This clearance is quite small (only 0.020" IIRC), and perhaps not every rebuilder holds to the spec. It would be prudent to check the clearance before installing any new water pump.
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