Joined: Dec 2018

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Half Drained SBC Block Cracking: Pic of engine includedHas anyone ever heard of a half drained SBC block or aluminum head cracking over night? Was replacing freeze plug behind the starter and wasn't able to finish. Left half the block half drained over night (did not drain complete cooling system), temp in Northern NM dropped to about 16 degrees during the night. Next morning after completing job, saw leaking coolant from stainless steel flexible exhaust pipe once engine was started after replacing bad freeze plug.

Little more background info. It is a rebuilt 327cu inch 350 HP, was a home rebuild. Running edelbrock e-street heads and air gap intake, HEI Distrib, hooker headers, holley carb. Only used 50/50 mix of store bought Prestone during time of engine install.

1st weekend of engine install. Got engine in, started right up, broke in new cam shaft at 2500 RPM for 15 Min. Open header, no thermostat, no transmission or no transfer case. Engine seemed to reach normal operating temp while break in, no serious leaking from exhaust or anywhere else. Things seems to be GREAT.........

2nd Weekend of install. Put transmission and t-case back truck. Took for about a 5 mile round trip got back home found a oil leak from oil filter adapter and a coolant leak from that pesky freeze plug. Cool, no biggie right? Mid week took ride to gas station to put gas, this time about a 12 mile round trip still no catastrophic leaking other than these two leaks mentioned above. Engine at normal operating temp both 5 and 12 mile rides.

3rd weekend this Sat. Fixed oil filter adapter leak ( missing oil filter adapter gasket), modified exhaust pipe on passenger side due to different headers as previously using, so cut and installed stainless steel flexible exhaust pipe to get around the tight fit in the transfer case and front drive shaft area. Started truck to check modified exhaust pipe for leaks, no exhaust leaks. NOT leaking coolant through stainless steel flexible exhaust pipe. Late afternoon decided to drain block on passenger side to start working on getting the freeze plug replaced. Removed starter, drained half the block from coolant plug on passenger side located by oil pan. Got freeze plug punched in to engine, got tired of wrestling with getting the plug out, lost day light and was cold from being outside all day and figured my best bet would continue in the morning....

Yesterday morning, got plug out within half hour, put new one in little hassle. Filled back with coolant few hours later to let sealant on freeze plug cure. Started the engine, got under truck for leak check and noticed coolant leaking through stainless steel flexible exhaust pipe I modified the exhaust pipe on. Convinced myself it was strange but not a big issue, got back into truck to go for ride. Immediately getting onto highway was smoking from passenger side tail pipe. About a mile down the road seemed to clear up, kept on for about a 10 mile round trip, truck ran pretty good. got home and was smoking immediately shut off the truck and had oil pouring out the back side of the engine. swiped some leaking oil with my finger and looked kind of milky. Checked dip stick and pretty freaking bad, knew it was not good. Realizing how bad the situation is didn't really care to look further into where the engine was leaking the mixed oil/ coolant from and here I am writing.

Think the engine block or aluminum head cracked over night? Where should I start investigating the problem?? Please keep comments positive as I have busted my butt last four months pulling out, rebuilding, cleaning and painting parts and yes spending money. I will answer any additional questions. Thanks..........

Joined: Jul 2014

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From: Marysville, WA

Joined: Jul 2016

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From: Wisconsin

Joined: Dec 2018

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Pre mixed Prestone and the heads were new out of the box. My dad was putting the motor together before he passed. But the fact that I got it up to normal operating temp three four times and had no issues makes me believe something happened during the replacement of the freeze plug maybe?