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Old 01-15-2007, 01:58 AM
skhorleb skhorleb is offline
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acid flush of Fresh water cooled engine

I have owned a 1974 C&C 30 MK1 for 2 years. I believe it has the original Atomic 4 (engine serial # 191095.) When purchased, she already had a fresh water cooling system installed, apparently installed a number of years ago. I believe a previous owner may have purchased it from Moyer Marine before the MMI 501 pedestal pump was available. An Oberdorfer model 201M is installed as the sea water pump. The temperature gauge has been dead since I owned it so I am uncertain exactly how hot the engine typically ran but I am confident it was within normal limits. Soon after a fresh engine paint job excessive heat symptoms appeared. It was very sudden and so intense that it started to bubble the paint above cylinders one and two. 'Still have good water flow out of the exhaust. I suspect the impeller is shot. Since there was no log of previous owner maintenance, I decided it was time to overhaul the cooling system. After replacing a bunch of components (i.e., all of the sea water and fresh water cooling system hoses, the thermostat with a Moyer late model Thermostat Spacer Kit, and the water temp gauge and sending unit), the fresh water pump will be replaced with a MMI 502 flange pump next weekend.

I don't know if the cooling system has recently been flushed or how clean all of the engine passageways are. I had the manifold off during the fall when I replaced the exhaust system. Those ports were cleaned out and observed very little scaling, if any; crud was not notable. In an effort to be thorough and proactive, I was considering doing an acid flush of the engine and heat exchanger. However, I have not found any specific references in the Moyer Marine Service and Overhaul Manual regarding acid flushing a FRESH WATER cooled system--only a sea water system. Is there any risk to running the diluted muriatic acid through the heat exchanger? Are there any special considerations for a fresh water system flush? I know I will need 2 5 gallon buckets for this--one to collect the current contents of the fresh water system and a second one for the acid solution. I planned on pinching off the hose from the plastic coolant reservoir before starting the flush so it's contents are not wasted, it does not dilute or contaminate the acid solution. Are there any unique steps to the documented acid flush procedure?

Thanks in advance.

Steve Horlebein
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Old 01-16-2007, 10:07 AM
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Don Moyer Don Moyer is offline
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A couple thoughts:

1) Depending on the paint you used on the head, or how thickly you applied
it, bubbling would not be unusual and would not be a certain indication of
overheating. I would therefore repair or replace your indicating system
before embarking on any other serious maintenance work on your cooling
system. I'm attaching a generic troubleshooting guide for testing gauges
and sending units.

2) Still on the theme of the paint as an indicator, it's difficult for me
to believe that an excessive overheating condition began just as (or
because) you applied the paint.

3) The fact that you have good flow out of the exhaust would go a long way
to exonerate the sea water pump performance as well as the exchanger

4) If you can see into the fill tube of the exchanger with the engine
running, you can check for turbulent flow just below the fill cap to
determine whether or not the fresh water pump is performing well. Closing
off the by-pass hose would also help diagnostically in determining whether
the thermostat may be malfunctioning.

5) If you get to the point of wanting to acid flush your freshwater cooled
system, it's really only necessary to flush the sea water side, which can be
accomplished in the same way one would flush a sea water cooled engine
except that the acid solution will address the sea water side of the
exchanger and the exhaust system instead of the engine itself. But again,
your normal flow of sea water out of the exhaust would seem to indicate the
sea water side of the system is OK.

In summary, even if you continue your work on the cooling system in a
preventive maintenance mode (not at all a bad idea), I'd still replace the
indicating system first so you can quantify your work and monitor your
engine temperature in the future.


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File Type: pdf Testing gauges and sending units.pdf (10.2 KB, 793 views)
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