Conference vicki::boats

From your description you have a raw water cooling system.  Simply described,
there is a pump in the outdrive that 'pushes' water to the engine's water pump.
That water is circulated thru the engine, exiting thru the exhaust mainifolds 
back to the outdrive where the exhaust/water is discharged back into the pond.

You are correct in your statement that salt water is flowing thru the engine 
if thats where you float it.

Tom

	I'll take a slightly different crack at it.  I have an old Chrysler
with a Volvo AQ 120/200 in it.  Mine happens to be raw water cooled and
functions similar to the description in .1, except in the Volvo application
the raw water pump is mounted in the front of the engine instead of in the
outdrive leg as in the Mercruser etc.  (this makes changing impellors much
easier)  I also have a boat I keep in the ocean which has fresh water (anti-
freeze) cooled engines.  Basically in the fresh water cooled application there
is a heat exchanger (which performs the function of a radiator in a car)
where the heat from the fresh water is exchanged (passed to) the sea water side 
of the loop.  I am familiar with two variations of fresh water cooling, one in
which the exhaust manifolds are cooled by fresh water, and one where the exhaust
manifolds are cooled by raw water.  In both cases the raw water goes overboard
with the exhaust in the exhaust "elbow" (the last piece on the outgoing end of 
the exhaust manifold assembly.  In the case of fresh water cooled manifolds 
there is a plate separating the water passages between the manifold and the
elbow, and the raw water exit hose connects to the elbow.  In the case of the
raw water cooled manifolds, the separation is made between the head and the
manifold, and the raw water exit path runs through the manifold and elbow.
In the fresh water cooled manifolds, larger heat exchanger capacity is usually
required, and in the raw water cooled manifolds the manifolds need to be 
replaced more often due to rot.  In both fresh water cooled variations the 
fresh water is circulated with a car type water pump, while the raw water is
pumped by a marine type impellor pump which can be direct or belt driven.
Fresh water cooling systems usually have a car type thermostat and keep the
fresh water loop in the 160-180 F range.  In a fully raw water cooled
application, the thermostat is usually set to maintain about 140 F.  This is
so salt chrystalization and build up will not become a problem as it can at
the higher temps.  Running the engine in the 160-180 F range usually provides
better engine performance, and possibly economy.  In my Volvo there is a
short section of exhaust hose which connects the exhaust elbow to the 
intermediate assembly (through transom section) of the outdrive.  There are two
bellows type hoses and one smaller hose which connect the outdrive leg to the
intermediate assembly.  The top bellows type hose is cover the drive shaft and
U-joint, the lower passes the exhaust and raw water discharge, and the small
hose is the sea suction for the raw water pump.
	Hope this makes some sense and doesn't ramble to much.

	Rick

    Thanks for the details so far, cant believe how much hassle it is to
    find out whats what. I've got dozens of books bout boats, youd think
    one would have an exploded view of this type of system. Looks like I 
    *may* have a raw water system. Will chek for the exit plumbing from the
    exhaust manifolds that Tom mentioned. Seems I may have a system similar
    to Ricks Volvo AQ, there is an 'extra' pump driven by a fanbelt that
    must draw seawater up from the IO. But there is no thru-hull plumbing
    to return the water, and the diagram in my manual shows only 1 tube
    coming up from the skeg. Jeez, maybe the hot water just turns to steam.
    Taking next week off, will have this nailed down, stay tuned... 

    Well, crawled around the bilge and followed the plumbing, seems raw
    water is sucked up to the engine by a fanbelt driven pump, piped to
    the back of the motor where it is distributed to the engines water pump
    and the manifold coolers. Water must exit with the exhaust, altho I
    have no proof of this. The manual does not show this plumbing, and my
    raw water pump is not working so I cannot see it coming out of the
    prop. I'm scratching my head on the mal-functioning pump. The impeller
    seems fine, and there are no restrictions from the water source to the
    pump, yet no water will come up. Thought it was a problem using muffs,
    so I switched to a barrel. No dice. Tryed priming it. No dice. Do these
    impellers have to be in MINT condition in order to move water?

>	Do these
>      impellers have to be in MINT condition in order to move water?

	Yes, I've seen impellors in my Sherwood pump for a PCM 351 that
"looked" just fine, but apparently were damaged enough, in some way, that
they wouldn't actually pump any water.

	BTW: I don't know about your pump, but mine *can* be bolted onto
it's motor brackets backwards and in this position, it also won't pump
anything.

Rick

    Looks like I'll have to change the impellor to find out. Should have 
    brought it with me to the Newport Boat Show last week, they had a booth
    pushing extended life impellors, sure looked like mine was in stock.
    Made of some slimy silicon substance that was is supposed to be self-
    lubricating and will survive dry pumping. Prices ranged from $40 -
    $120.
    
    Dirk