So I had a look at the 186s motor
My 161 and hi comp head motor
And a blue 173 under the bench.
Seems all blocks have the little cast tunnel in the block from the water pump into the block up into the block deck , separate from the water in the block.
All the heads except the hi comp have a cast tunnel from the bottom of the head where is meets the block then up into the bottom of the thermostat
So the water flow in the head is separate to that in the lower of the thermostat outlet.
So both outlets on the passengers side would work with a heater.
My hi comp head unfortunately has no cast tunnel in the head separate, just travels from the block up into the normal water cooling of the head. See pic with red wire in it. And my head numbers
This also means its a direct by pass from the water pump to the head , dead heading?
I presume 149s are the same.








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