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Thread: Castech #607 Keep or junk them?

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    Join Date
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    Castech #706 Keep or junk them?

    Questions on the Castech #706 casting coolant leak problem?
    Does the leak start only after the engine has been once over heated or do they just start leaking?
    Is the “Genuine GM (122378255) Fluid cooling system seal tablets” a good preventative stop leak measure on a non-leaking #706 heads?
    Should I keep my #706 non-leaking as of now heads or buy used #862 heads and overhaul them?
    The reason I am asking is that my next mod is to do some head porting [valve seat to port blending and better the only-two angle stock seat angles] and checking the exhaust port to header size. Maybe increase the combustion ratio, and check the valve train geometry.
    I can buy a pair of #862 casting heads at the local salvage yard for $175, either a 1999 or 2005 heads from 5.3 pickups. They are still on the blocks and will take a look before buying them.
    I bought the 2002 truck new and now have 80,000 miles on it. I know that the #706 heads are the smoother SPM castings and flow better pre-porting than the sand cast #862s.
    Thanks in advance for your input.
    Last edited by metalchips; 03-23-2019 at 01:24 PM.
    2002 GMC 1/2 ton Sierra,4WD, Xct cab, camed, mid-length headers, Nelson tune, electric rad. fan, trany cooler, Heavy 5750 lbs with topper.

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