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  #1   IP: 69.138.241.121
Old 04-30-2005, 07:01 PM
Jeff Jeff is offline
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Water "Batching"

I'm a relatively new boat owner and A4 ("new" model) enthusiast. I attended last winter's seminar in Chestertown weeks after purchasing my Columbia 8.3 and let most of the discussion fly right over my head. In my sophmore sailing season I'm finally figuring some things out but there's always more to learn.

I've just been reading some posts and came across a few references to water "batching" out of the exhaust. Specifically, you clarify that while the water will batch at idle it should flow continuously at cruising speed. I believe the water batches out at all times.

I'm wondering whether this is related to another problem I'm having, which is that the temp. never exceeds 120. When I got the boat last year it was overheating. I determined that the screw holding on the cam shoe was a replacement that was set in too far and gouging the impeller blades. I installed the parts from a service kit as well as a new thermostat (which I've tested through a double boiler on the stove to determine it is accurate) and it hasn't been above 120 since. I believe the "problem" is that the cam shoe is so thick it causes extra "thrust" if you will of water (though I may be totally off base). I attempted to reinstall the old cam shoe but could never find a screw that was appropriately sized and that did not result in water leaking through the screw hole (even when I applied liquid gasket).

I guess this long-winded description leaves me with several obvious questions: (1) What should I look for as the source of the batching exhaust? (2) How concerned should I be with the water temp.? Other than buy a new water pump (which makes my wallet cringe this time of year) is there anything specific I should do?

Thanks!
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  #2   IP: 38.118.52.76
Old 05-02-2005, 08:52 AM
Don Moyer's Avatar
Don Moyer Don Moyer is offline
 
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Jeff,

Here are the answers to your questions:

(1) What should I look for as the source of the batching exhaust?

Water "batching" out of the exhaust at idle is quite normal, due to the fact that there is not enough exhaust flow (in terms of volume) to keep the engine cooling water moving through the exhaust system continuously. At idle, a head of water builds up within the water lift muffler until the pressure of the exhaust increases sufficiently to move it through the system.

The volume of engine exhaust at normal cruising RPM should be sufficient to keep the cooling water moving through the exhaust system continuously, with a resulting back pressure of 1 - 1/2 psi or less. The few times that we heard about cooling water batching out of the exhaust at cruising RPM, it was determined that the design of the exhaust system had effectively incorporated two water lift systems. In most of these cases low points within the hot section collected water which had to be "batched" into the real water lift muffler and in at least one case a prior owner had actually installed a second water lift muffler.

When water batches out of the exhaust system at cruising RPM, there is usually some other symptom of higher than normal exhaust back pressure, including fouling plugs, caramelized goo on intake valve stems, and/or black goo within the carburetor intake.

Here is a copy of a recent technical note on the subject of exhaust back pressure:

Normal desired exhaust back pressure for the Atomic 4 is between 1-1/4 psi and 1-1/2 psi. Exhaust back pressure between 1-1/2 and 3 psi usually results in sootier than normal plugs and can lead to carbon buildup on valve stems. Back pressure from 3 to 5 psi can cause caramelizing of intake valve stems, and pressure over 5 psi causes a "gagging" sound as the engine tries to accelerate; droplets of gasoline might be seen discharging from the intake of the carburetor, and in extreme cases of exhaust blockage, the engine may not start, or even run better if one of the spark plug wires is removed. In this case, the exhaust system is adequate for a three cylinder engine, but not for a four cylinder engine.

(2) How concerned should I be with the water temp.? Other than buying a new water pump (which makes my wallet cringe this time of year), is there anything specific I should do?

Your engine is not going to suffer any significant damage from your lower than normal operating temperature in the short term. So you don't have to stop using your boat while you continue to look for the cause of the over-cooling. In terms of your cam shoe, most of the Atomic 4 fleet in active service today is probably using an M-7 cam shoe without experiencing an over-cooling problem, so I do not recommend replacing your pump.

There are really only three things that can cause engines to run cooler than the thermostat rating would indicate:

1) Water is getting through a partially stuck open thermostat.

2) Water is somehow getting around a properly functioning thermostat.

3) The gauge or sending unit is malfunctioning (usually the least likely).

The first two of these possibilities are sometimes aggravated by a partial restriction within the by-pass loop (between the "T" fitting in the center of the water jacket side plate and the inlet to the thermostat housing).

It's rather difficult to visually inspect the current thermostats from Westerbeke without the "breathe through" test. When looking in from the top of the thermostat, the moveable disk may appear to be down and closing off the opening in the center of the housing, when in fact, it's raised off the housing by 1/16" or so.

In terms of the second possibility, water can sometimes by-pass around the base of a thermostat if the top of the head (where the thermostat seats) has eroded away to some extent. In these cases, the overcooling can be remedied by installing a spacer under the thermostat. If you find this fix to be necessary, you will need to replace the two thermostat housing studs with manifold studs. The manifold studs are slightly longer and accommodate the thickness of the spacer.

Relating again to the second possibility, water can move around the base of a properly functioning thermostat if the groove around the base of the thermostat housing is eroded away, leaving the thermostat to rise up slightly off its seat.

Best regards,

Don Moyer
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