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  It started,ran for 6 min. then freeze plug blew

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Author Topic:   It started,ran for 6 min. then freeze plug blew
66bluefb
Journeyman

Posts: 89
From: Okla.City,Okla.
Registered: May 2002

posted 07-31-2002 10:28 PM     Click Here to See the Profile for 66bluefb   Click Here to Email 66bluefb     Edit/Delete Message   Reply w/Quote
After months of building my 302 I finally started it tonight. Ran it at 2,000 RPM for 6 minutes when the freeze plug blew out of head. The guy that rebuilt the heads didn't replace the freeze plugs, damn it. I know your supposed to run motor for 20 minutes so what I want to know is it screwed up. It sounded real good but the rockers were a little loud.Thanks,Tony

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steve'66
Gearhead

Posts: 4307
From: Sonoma,CA,USA
Registered: Mar 2000

posted 07-31-2002 10:29 PM     Click Here to See the Profile for steve'66   Click Here to Email steve'66     Edit/Delete Message   Reply w/Quote
How hot did it get?

SteveW

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66bluefb
Journeyman

Posts: 89
From: Okla.City,Okla.
Registered: May 2002

posted 07-31-2002 10:44 PM     Click Here to See the Profile for 66bluefb   Click Here to Email 66bluefb     Edit/Delete Message   Reply w/Quote
I don`t know for sure,I just have the gauge that has C H It was about a 1/4 of the way from cold.Thanks,Tony

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steve'66
Gearhead

Posts: 4307
From: Sonoma,CA,USA
Registered: Mar 2000

posted 07-31-2002 11:19 PM     Click Here to See the Profile for steve'66   Click Here to Email steve'66     Edit/Delete Message   Reply w/Quote
Could be a head gasket leak that added combustion gases to your coolant and raised the pressure enough to blow the freeze plug. A leaking head gasket can blow the cap off the radiator even when the coolant is cool.

SteveW

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66bluefb
Journeyman

Posts: 89
From: Okla.City,Okla.
Registered: May 2002

posted 07-31-2002 11:36 PM     Click Here to See the Profile for 66bluefb   Click Here to Email 66bluefb     Edit/Delete Message   Reply w/Quote
Steve, I didn`t have coolant in it I just had water.The heads have 54 cc and are ported with 194 / 160 valves.Thanks,Tony

[This message has been edited by 66bluefb (edited 07-31-2002).]

[This message has been edited by 66bluefb (edited 07-31-2002).]

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bluestreek
Gearhead

Posts: 827
From: Athens,GA
Registered: Jul 2001

posted 08-01-2002 12:36 AM     Click Here to See the Profile for bluestreek   Click Here to Email bluestreek     Edit/Delete Message   Reply w/Quote
The motor should be OK.. Most cams wipe out in the first 5 minutes anyway. Get her patched up and try it again.

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SteveLaRiviere
Administrator

Posts: 24286
From: Saco, Maine Toys: '70 Mustang Mach 1 - '72 Mustang Sprint - '94 F-150
Registered: May 99

posted 08-01-2002 07:49 PM     Click Here to See the Profile for SteveLaRiviere   Click Here to Email SteveLaRiviere     Edit/Delete Message   Reply w/Quote
Blowing a freeze plug is pretty strange, I think SteveW might be on to something.

When you installed the heads, you carefully observed the 'Front' markings on the head gaskets, right?

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steve'66
Gearhead

Posts: 4307
From: Sonoma,CA,USA
Registered: Mar 2000

posted 08-01-2002 08:08 PM     Click Here to See the Profile for steve'66   Click Here to Email steve'66     Edit/Delete Message   Reply w/Quote
When you fire it up again, let the engine warm up with the radiator cap off. If it boils over before the water gets near boiling, you've got a head gasket leak.

Don't ask me how I know.

SteveW

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DidgeyTrucker
Gearhead

Posts: 760
From: Nashville, TN USA
Registered: Oct 99

posted 08-04-2002 02:25 PM     Click Here to See the Profile for DidgeyTrucker   Click Here to Email DidgeyTrucker     Edit/Delete Message   Reply w/Quote
The freeze plug could have been weak in the first place, since it wasn't replaced in the rebuild. A little pressure, and POP.
You're supposed to keep the rev's up on a new cam for the first 20-30 minutes, so the cam manufacturers say. This keeps oil splashing on the cam for lubrication and cooling while being run for the first time.
It doesn't have to be continuous. You didn't kill it by shutting it off after six minutes.

Do you have a bicycle pump? You can make a poor man's pressure tester for the water passages. Get a freeze plug with the outer diameter that will fit in a radiator hose. Drill a hole and mount a tire valve stem in the freeze plug. Also plug the other hose. You can now pressurize the cooling system to check for leaks! If it holds pressure, good. Remember, the normal pressure is never over 15 pounds, so don't try pumping 90 pounds in there.

Tracy

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