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Cooling system pressure

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rayb

Member
"Hi guys I'm back again. I

"Hi guys I'm back again. I have a LM318 which has behaved normally in the cooling system up until now. The motor has a closed cooling system using normal coolant.

The boat is on a mooring about 140 miles from home so I only get to it every second weekend religiously.

On arrival I immediately check fluid levels etc etc. The last two trips I have found the cooling system to be fully pressurised, and when taking the cap off, coolant sprays out over the motor even though it is cold ( ambient temp about 25 degrees ( centigrade ) and two weeks since the boat has been used.

How can this be ? and why does it occur now and not in the past ? Has anyone had a similar experience or able to offer me some advice.

Any and all replies will be sincerely appreciated."
 
"G'day Raymond,

At firs

"G'day Raymond,

At first I scratched my head when I read your post. Then I thought about it and realized there are compressed gasses in the cylinders and to a lesser extent in the exhaust. Hopefully that is not what is pressurizing your cooling system.

I found these notes in a Mercuiser service bulleting online. Seems potenailly applicable to your situation.

http://www.bmwmarine.org/info/Mercruiser%2089-16%20D636%20overheating%20%20.pdf

If the cooling system is prssurized, check for a head gasket leak or exhaust gases entering closed cooling system.

If higher pressure is obtained than listed below, exhaust gases may exist in system.
Coolant System Pressure
800 RPM (idle) 6 PSI (41 kPa)
3800 RPM (WOT) 20 PSI (137 kPa)

Check the following if excessive pressure or gas bubbles are found.
a. Head gasket leakage by making a compression test.
b. Exhaust gases existing in the closed cooling system by using a combustion leak tester.

NOTE: Snap-on Tools has combustion leak tester available for testing coolant for exhaust gases. (BlockCombustion Leak Tester P/N GA170B)

Kits are available to measure the pressure at the heat exchanger cap.
http://www.autobarn.net/xxx7990.html

Good Luck,
Chuck"
 
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