[C38] heat exchanger

[Tom T.]

Hello Patrick,

Most heat exchangers are welded closed and not really easy to completely clean without an oxyacetylene torch and silver solder to take at least one end off of the heat exchanger.  Most blockages are in the sea water intake side of the exchanger where the hose from the water pump enters the exchanger.

The exchanger is just a copper tube with 1/4" tubes inside which are surrounded by sea water.  The outer most hose barbs on the exchanger are for sea water and the inner two barbs are for fresh water.  There are plates welded inside near the end caps with holes drilled in them holding the welded in place tubes creating chambers on the ends which flow through the tubes and an inside chamber of fresh water that surrounds the tubes.  

When an impeller breaks apart, the larger pieces will end up in the upstream side of the exchanger, the pump end.  In that end cap the pieces will then block the small 1/4" tubes inside.  By reversing the flow with flushing water, you can usually discharge any blockage minor.  This means flushing from the exhaust riser hose and letting the water escape from the pump end.

You should be able to blow through both chambers fairly easily if they are not clogged.  If they are clogged, any good radiator shop can boil them out for you without having to un weld the end caps which is a last resort remedy.

One fairly common mistake on heat exchangers is to have the fluids run in the same direction through the exchanger.  The fresh water should always go in the opposite direction of the salt water.  This ensures maximum temperature differential between the exiting fresh water and the temperature of the exiting sea water.  By reversing the flows, the fresh water exits colder and the sea water exits warmer giving maximum cooling efficiency.  I have heard of overheating boats that just reverse flowed their exchanger hoses and it fixed their overheating problems.  That is how important a reverse flow is but I know that is not your stated blockage problem, I'm just making a point.

While I digress, it's important that the fresh water hose coming from the engine goes to the water heater before it goes to the heat exchanger.  This makes the water heater much more efficient but does nothing for cooling the engine once the water heater is heated to near the thermostat temperature.

The exchanger zinc should be checked and probably replaced every year or sooner, depending on your boat's individual requirements.  Some boats can keep zincs a long time, others eat them up pretty regularly.

You should be able to just pull the sea water hoses from the pump and exhaust riser for the reverse flow test.  Run pressure water in the riser hose and put the pump hose into a bucket to see if any pieces of hose come out when you reverse flush.  This procedure alone should fix your problems if you do indeed have minor blockage in the sea water side of your exchanger from impeller pieces.  If your blockage is marine growth, you will need to pickle it with cleaners but it should eventually flush free.  Most blockages if not all are in the sea water side of the exchanger closest to the raw water pump. 

After you run this fresh water flush, you should still blow through the riser hose to check for a free flow.  You should be able to blow fairly easily through a clean exchanger.

Sorry for the long ramble but I hope this helps.

Tom Troncalli
Renata  hull #95
St. Pete, Fla

 


----- Original Message ----- 
From: Patrick Harpole 
To: Catalina 38 Listserve
Sent: 2/24/2009 9:13:44 PM 
Subject: [C38] heat exchanger


Skippers,
     I wrote and appreciate your answers/help about impellor breaking up and engine over heating.  Then there was the problem of the black smoke emanating from the engine compartment.  Someone mention it might me rubber parts of the impellor getting into the heat exchanger? 
Does anyone know how to access/clean heat exchanger?
Thanks,
Patrick……aka  “Blue Eyes”  
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