Closed cooling leak

bobbarry

Member
Feb 19, 2016
31
South west Florida
Boat Info
Sea Ray 350 Sun Dancer, 1990
Engines
Mercruiser 454 with v-drives
I have 1990 454's (Gen IV, I think) I am loosing anti freeze on the starboard engine while at the dock (Not running). I inspect the anti freeze and the tank will be down about 1/8 to 1/4. Refill and check it a couple days later and it's down again. I haven't run the engine. I can't see where the leak is. Any suggestions? Thanks.
 
get you engine oil analyzed. If that checks out clean then it's not that big a deal. Throw in some radiator stop leak. If it's not in your bilge it's more than likely an internal leak in the HE.
 
Most likely you have an internal heat exchanger leak. The tubes can fail and the coolant will leak into the raw water cooling side and go out the exhaust. You can get a radiator pressure tester from Harbor Freight to pressurize the heat exchanger. Unless the coolant is going into your engine oil it has to be going out the exhaust thru a failed heat exchanger.
 
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Did you change the coolant just before this loss began?
 
If your heat exchangers are over 5 years old you should replace the ones on the oil and transmission mr cool sells them for about $100 each. The main engine one take to a rad shop. They will clean it, repair any tubes and paint it so it looks like new for about $200. I had an oil cooler fail once. Sucked salt water into engine oil when engine cooled. Caught it before I ran the engine. Took 4 oil changes to get the salt out.
 
Found it. Ran the engine and saw a fair amount of antifreeze running out of the radiator cap. Old cap and apparently the gaskets were worn out or just really dry. New caps seemed to solve the problem. I did check the exhaust for steam or evidence of antifreeze. Thanks all of you. I kept all the suggestions since these are old engines (1990).
 

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