problems with my 4.3L mercruiser internal cooling.

407bull · 08-01-2009, 12:04 PM

I keep loosing coolant no leeks on the outside, it has been pressure tested no problems. But when it heats up the coolant disappears slowly. Any suggestions?

fishkisser · 08-01-2009, 02:28 PM

If its not going into the crankase oil it has to be going out the exahust ..
Via a blown head gasket or corroded exahust manifold ...
Putting some brightly colored food coloring in your closed cooling system
might help you find out whats up ...
Good Luck ... Barney

BIGCSS · 08-01-2009, 04:59 PM

Do you have a coolant recovery tank that takes the overflow from the heat exchanger? If not you are losing some coolant when everything warms up it has to have a place to go, if no tank it just runs out the little hose into the bilge, but if you have a coolant recovery tank (like a car has), then it will pull it back into the heat exchanger when it cools. My Kodiak 350 didn't originally have a recovery tank and it would lose some coolant, so we went and purchased a recovery tank kit at an auto parts store and installed it ourselves. It was less than $20 to solve this problem.

KingSalmonBoy · 08-01-2009, 05:20 PM

Could also be the intake manifold gasket. Look under your oil filler cap, if you are using dexcool it will be orange. Good news is they are not that hard to replace, just get a quality replacement gasket with metal rings that go around the studs/bolts.