Coolant Leaks

[Terra Nova]

I have a 2002 410 Sport Sedan. 8.1L Mercruisers for engines. Marina winterized the boat. When I came back in this spring after the boat was launched, the coolant on both engines was all in the hull. Both reservoirs let go. Marina did a check and said it was the coolant reservoir plugs and replaced those. Came back this weekend noticed that there was small amount of coolant in the hull on each side. Ran the engines in the slip for 30 mins taking them up to 2000 rpm and 3000 rpm for about 3 mins each time. No visible leaks during the test and reservoirs stayed at the same level. Left the boat to cool and checked it again the next morning. No visual leaks in the hull but the port engine reservoir is down about a 1/3. Starboard down slightly.

Any ideas on how the coolant level dropped but no visible leaks?

[km1125]

You might have had some air bubbles in the system that had to work themselves out.

I'm curious about happened to the "reservoir plugs"... did they leak or just fall out? Do you have a pic of these?

I wouldn't expect a leaking reservoir to drain all the coolant in the engine, just what's left in the reservoir.

[Viper]

Post an engine serial number, I want to check something that might apply to your application.

[plittle2005]

If the heat exchanger is leaking internally, higher pressure coolant will be forced into the lower pressure water side. The coolant will then go out the exhaust with the raw water.

if you pull the HEX anode out and coolant comes out, the tube bundle has failed, and coolant will disappear. In any event, have the HEX's pressure tested, can be done in the boat

[pepmyster]

I've had to adjust the level in mine a couple of times, since I check everything before I go out anyway. Not a perfect system but the air pockets do work themselves out. I'm following this one for sure, the more we learn........

[bud37]

Coolant level drop down on engine cooling ( when the engine cools it pulls from the reservoir ) is normal when there has been coolant problems /leaks etc. A few cycles should take care of the lower fluid level. Now if it continues to a large amount then as mentioned a pressure test is in order to confirm the cooling system integrity.