Air Bubbles in closed cooling system

[mestey2004]

Hi, I have a mercruiser 305 5.0 1999 with a closed cooling system. My problem is I keep getting air in the system. Which of course makes the engine overheat. I have tightened everything I can think of, but the bubbles continue to come out of the fluid fill area. At first I thought that I didnt get all the air out, but the fluid level does not go down as the air comes out. <br /><br />Would a water pump failure cause air bubbles like this? Is there something I sould be coating the hoses with before installing them to get a perfect seal? I have seen no leaks in the system, just air, so the problem should be where there is suction, not pressure. Right? Not sure where to go from here.....<br /><br />Thanks

 

[Bob_VT]

Re: Air Bubbles in closed cooling system

Uhhh.... getting air in the system is also an indicator of a possible blown head gasket.<br /><br />Bob

 

[mestey2004]

Re: Air Bubbles in closed cooling system

Wouldnt I get water in the oil?<br />The oil is totally clear

 

[DJ]

Re: Air Bubbles in closed cooling system

Not necessarily.

 

[tommays]

Re: Air Bubbles in closed cooling system

i have had the same thing on two cars and it was head gaskets both times bubbled the overflow tank like a air compressor was connected<br />tommays<br /><br />a auto type raditor pressure tester should show a leak

 

[mestey2004]

Re: Air Bubbles in closed cooling system

Crap. Thats not good news. Any way I can check it before pulling it appart?<br /><br />Thanks

 

[mestey2004]

Re: Air Bubbles in closed cooling system

it is not bubbling very hard, just a trickle really. sort of like a leaky balloon under water

 

[mestey2004]

Re: Air Bubbles in closed cooling system

http://www.boatfix.com/merc/Bullet/01/01_13.pdf <br /><br />for future reference. Im going to check the spark plugs for water. then pull the water pump and reinstall the gaskets to be sure I have a good seal there. If it persists I'll pull the head(s). Of course if I find water in the plugs then I;ll do the heads.<br /><br />Any more thoughts?<br />m

 

[BB5401000]

Re: Air Bubbles in closed cooling system

When you have bubbles in the coolant it indicates leakage from the cylinders or combustion chambers into the cooling jackets through a bad head gasket, cracked head, or cracked block. You can usually isolate which cylinder is bad by a compression check. The cylinder that has a low pressure reading is the culprit. Another trick is to pressurize the cooling system and look into the cylinders to identify which one is filling up with water (usually caused by a head gasket, but may be head or block also). At the very least, the heads will have to come off to see if the head gasket is bad. You will probably notice the fire ring distorted or burned through. While the heads are off, have them inspected for cracks, valve condition, etc. and repair as necessary. At worst, the block will be cracked and need replacement.

 

[mestey2004]

Re: Air Bubbles in closed cooling system

Thanks for all the advice. Looks like I;ll be pulling the head(s) once I inspect the plugs to find out what side it is on. Time to pull the book out again. Sigh...