Bleeding Cooling System Universal M25

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Mark15143

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Jun 12, 2004
38
- - Long Beach, CA
Blew a hot water heater hose and lost coolant and overheated engine. Have 1985 C36 and after fixing hose and replacing coolant - cannot get the system to circulate. I assume I have an air lock. Was told to bleed air from petcock at top of thermastat - any other experience or ideas out there. Would sincerely appreciate the help. Mark - Long Beach, CA
 
C

Calif. Ted

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Jun 8, 2004
2,928
Catalina 320 Dana Point
Usually a bleed valve at the water heater

also, heater is highest part of system and tends to develop air lock there.
 
D

Dave4823

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Jun 4, 2004
19
- - Long Beach, Ca
Fill The Hoses And Give Her A Little Gas

When changing the water heater or hoses it's advisable if possible to pump a little coolant through the heater and hoses prior to connecting them to the engine. Disconnect the two hoses at the engine and used a small hand pump to fill the hoses and water heater with coolant. Then reattached them, don't worry if use loose a little coolant when hooking them up. Now for the secret, when bleeding the system you need to open the butter fly valve on top of the thermostat housing and then rev the engine up any order to move the air through the system. Most people don't bring the engine to high enough rpm's to bleed the system. When bubbles and air are replaced with coolant coming out of the bleed valve, close the valve and top off the coolant. This bleeding process should take no more then 2 - 3 minutes and the engine should not over heat during this time. Good Luck, Dave
 
M

Mark

Variation on reply 1

I found it worked best to remove the thermostat, replace the top, use a small plastic tube in the petcock (butterfly valve)and vent it into the mainifold top. That way you recover all anti-freeze and you can vent longer and more completely. You do have the run the RPM's up aways for several minutes at a minimum. When all the air is vented, close the petcock, shut down the motor. Let it cool, replace the thermostat. (you will lose a very small amout of colant when you remove the top. When everything is back together, top off the coolant to the proper level.
 
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