antifreeze loss

I am losing antifreeze in my 5.7 crusader starbd engine on 29 tiara. I have refilled overflow twice. No signs of leakage in bilge or on engine. I ran a pressure test and no pressure loss after a full day. No sign of water in oil. any suggestions. the boat runs fine no missing. Pulled several plugs (not all) and no signs of water there. any ideas>

do you have a heat exchanger?
maybe your leaking it out into the sea water which means seawater might get into the engines.
are the engines FWC or raw water cooled?
Or the headgasket is going and it is going out the exhaust.

are sure your engine pumps are not leaking?

"Anti-freeze" usually means FWC, w/ HX...

I think I'd have another go with the pressure tester and maybe some clean white rags/paper towels.

It could also be going out the exhaust via a leak to the raw water side.

How old is the engine and how "fast" is the leak? Do you fill the bottle to the fill mark or to the top?

On the pressure test, make sure the HX is full or nearly full. You don't want air in the system for this test. If it checks out good cold, redo it after a warmup.

some answers to the questions posted. the engines are 2004 with 350 hours on them. they are fwc and yes I have a heat exchanger. I have filled overflw to max level, but after several runs it is emptied. I have not put down rags or paper but there is no visible signs in the bilge. If there is a breach to raw water and going out exhaust, can raw water get into engine? I will attempt another pressure test...

Several areas that may cause loss of E/G coolant:

Of course, one would be a bad head gasket.
One may be a cracked cylinder head.
Another may be an internal leak within the H/E.... leaking pressurized coolant into the sea water side.

Is this a Full System? (i.e., are the exhaust mans included in the Closed Cooling system loop?)
If so, this may be a bad exhaust manifold, leaking pressurized coolant into the exhaust flow.
If so, what type of seperation is used between the manifold and riser? (could there be a breach here?)

Note that the H/E's recovery system only returns coolant as the coolant cools, and a mild negative pressure is realized within the H/E. It's a siphon principle!

Maybe try NOT filling the recovery reservoir, and see what occurs during a short test run (although you say that you see no physical signs of leaking coolant).

I would also remove the other spark plugs that you did not remove previously. No sense in stopping part way through a "check" that may reveal a location!

A little off topic but my 2001 F-150 is starting to eat a little A/F and with 246,000 miles on it I will bet it is now becoming part of the exhaust gas. NO other tell tale signs so you may be experiencing similiar conditions, You have low hours on a relatively new engine but there is a lot to be said for previous use and maintenance. You may want to check all of your fittings to insure no loss there and since air in the system can skew your results, as Dave said...be sure it is filled well

Yes, there are more hose clamps on those systems than most initially imagine - make sure they are all tight.

Another item to check is the zinc in the HX, especially if you've never changed them. If all that is there is the pipe plug, the HX could be suffering from galvanic corrosion.

Don't forget to check the cap when you get the pressure tester back out; they are known to leak.

Another thing you can do is use your nose. The antifreeze has a very distinct odor and a sniff test may help. a good visual inspection of each joint/connection may help find a "leak trail". The last "lesson learned" is that some leaks are small and, with a warmed up engine, can evaporate pretty quickly.