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2000 MC 5.0 Bravo 3 0m012817 Coolant being forced out the overflow tube

rick3452

Regular Contributor
Since I replaced my impeller and lost the coolant during the change, I refilled the system and on the first ride I checked the engine compartment to see the bottle was full and coming out the top of the overflow bottle.

****UPDATE**** So after all the great information I went out this am and saw that the FULL bottle had returned back to the system..

So I went to boat supply place and picked up a new pressure cap (14), could not find a 16. Bought new correct coolant, drained the HE, refilled according to mercruiser method, ( thanks Boat Tech) started it up and went for a cruise down the inter coastal about 1200 RPM's the whole time.
Within 20 min. to a half hour it was apparent that the bottle was once again filling. and by 45 Min. it was coming out the overfull on the bottle. So turn around head back to the dock, ( by the way TEMP was always a perfect 165) but I was concerned that eventually I would be low on coolant and overheat as it continued to pee out the top of the bottle. (never budged of 165) So here's what I observed, while my wife was driving I felt all around the H.E the top near the cap was hot, and most of the top was hot, but the end caps were almost cool to the touch as well as the bottom. I did pull the two end caps off just to see if there was a blockage and there was nothing. I just can't figure out why the coolant is being forced out the over flow hose. 1.5 years ago I did have the H.E repaired for leaking tubes but it has been good since. By the way NO BUBBLES and engine is running perfect. Thanks for the help I really appreciate it. Rick
 
..picked up a new pressure cap (14), could not find a 16.
2 PSI is over a 15% difference. You may have exhaust gases entering the cooling loop even though you don't see bubbles.
 
Thanks Guy!

I think we have it…. I spoke to a good guy at "Partman" Marine supply and after explaining that a year and a half ago I had my H.E repaired because there were 5 tubes that were leaking. His theory was that if the 5 already failed, the rest would soon be failing too.

So what appears to be happening , like Bondo and others have suggested is that the H.E is failing, and adding quite a bit of seawater to the coolant. It also made sense due to the fact that the overflow leaking out was not "true green" antifreeze and was just a faint color of green with almost no coolant smell. Thats why after losing all the overflow, the H.E. was still full upon return.
Ordered a new one today.
Thanks again for all your help…. Truly a great community of people.
Rick
 
If seawater has entered the cooling system you will need to drain, flush and refill the entire system. Good luck.
 
Bottom left are links to pdfs of Mercruiser cooling systems. They show all of the system drain points. I raise the front of the trailer a little to allow better drainage from the bilge and then open all the drain points. Capture the old coolant and recycle it. Close the drains finger tight and refill with fresh water, run the engine on muffs for 5 min. and drain again then close the drains and refill w/50:50 antifreeze. Any brand of modern green antifreeze will work.
http://www.marinemechanic.com/site/page19.html
 
If you are near an AUTOZONE store you can borrow their pressure tester for radiators. After your repairs connect it in place of the cap and pump it until it reads 16 psi. It will hold pressure if there are no leaks in the closed cooling circuit.
 
Thanks Guy, I ordered a brand new H.E so I'm thinking I should be good to go. But with the introduction of sea water into the system….Isn't it the same as someone that has a "standard cooling" system and not a closed system??? So I'm assuming that there would be no damage done because of the sea water circulating...
Thoughts??
Thanks again, Rick
 
The pressure test is just another security blanket to ensure there are no other cooling system issues. Why do all the work and find out on the 1st trip out that you missed another issue? JMHO
 
Most (if not all) HEs have a zinc pencil on the raw water side. Usually installed via a 3/8 brass plug. Inspect/clean or replace annually.
 
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