I have a 1990 Bayliner Ciera 2655 with Mercruiser 7.4 bravo engine 454. How do I get air out of the engine?

Question

The motor over heats. I have put a brand new sea water pump, thermostat and also replaced a couple of hoses. I then took the rear end off, cleaned and greased everything, checked to see if anything was clogged, flushed everything with water and the boat is still over heating. The engine gets the water to the thermostat but when it gets to the circulating water pump, no water gets to the hoses and it over heats. Could it be that I have an air bubble in the engine? If so how do I bleed the air bubble out.

Answer 1

Did you perhaps see a brass fitting on top of the engine? Closed cooling engines do use anti-freeze solution. they also overheat right now if you do not bleed system; plug on top of thermostat cover. Take to a expert technician, he should be able to figure it out. Too many possibilities. There is a certain order that the thermostat housing and thermostat and spacer has to go togrther also

Answer 2

Don't worry about any air in the system, that's not the problem.  When you say "sea water pump"  is this pump mounted to the engine?   This boat normally has a water pump in the stern drive.  However on some boats an "aftermarket" fresh water kit was installed.  It has a heat exchanger.  Then a much larger water pump was needed, so the merc. engine mounted pump installed.   There were also some problems with the gaskets on the riser's.  There is a service bulletin about that.  I guess it's possible that the hoses aren't hooked up right.  But, just take the thermostat out, put the housing back in place and try the engine.   Ok, it's unusual but it could be the circulating water pump!

Answer 3

Sounds like it is not a closed system>Check the risers to see if there plugged> as that is where the water goes to>Take the hoses off going into the Exhaust risers 1" hose> see if water flows when you start it> let run and see if there is air bubbles in it> Don't run to long as the exhaust housings will warm up> If no bubbles check risers as there are small holes in the exhaust side for the water to exit as that's what cools the exhaust>

Answer 4

Sounds like your circ pump is shot.  Rare, but it happens.  How's your water flow with the thermostat removed?  Be careful, those big blocks heat up QUICK! By the way, for the other answers,  Bravo drives do not have an impeller pump in the gearcase, but a "seawater pump" mounted externally on the motor.