The water temperature will soon reach a steady state once the heater
temperature 'equilibrates'. Typically such a heater will come up to
temp quite fast. My 7 gallon heater will heat to 'hot' water from the
engine loop in about 10-15 minutes. Was the same with an Atomic 4 as
it is with my 3QM30. Actually the cooler the water in the manifold is
actualy better ... less carbonate (salting) deposition.... and heat
transfer is regulated by the 'log mean temperature difference' - the
cooler the inlet water the better the overal heat transfer.

In article , GBM
wrote:

"Rich Hampel" wrote in message
...
You are right as I was thinking of the 2QM20 (or 3QM30) ... which is
arranged the way that I stated but has the Tstat in a separate housing
that fits into the top of the fresh water tank on the heat exchanger..


Rich - What do you think about the fact that the water leaving the heads
would be cooled (In the water heater) before it returns to the manifold. It
would soon get hot again, but the manifold would be slightly cooler than the
block.

And, the thermostat would not open right away (Until water heater is hot),
so engine would presumably run hotter for a while.

GBM