blown head gasket - The 1947 - Present Chevrolet & GMC Truck Message Board Network

daveccpa · 05-22-2020, 12:13 PM

My son blew a head gasket on his truck LT1 SBC 350. He's back at college so I'm trying to fix it for him. Any suggestions on flushing out the block of the water that got in it?

We drained the block literrally right after the gasket blew and it's been sitting for a month now. I took the valve covers off and there is a bit of rust now on the inside of them. The valves look fine. Just trying to decide if I pull the whole motor and rebuild or just fix the gasket and go on.

My son wants to replace the engine in a few years anyway so maybe its best to just replace the gasket and do what ever else to keep it running.

vince1 · 05-22-2020, 02:16 PM

Isn't there a plug at the bottom of the block to drain the water? I don't know if on one side or both. Taking off the lower rad hose should also drain most of it. Drain the oil and put in fresh before re-starting it.

**truckster** · 05-22-2020, 02:43 PM

Please clarify - are you trying to drain the coolant passages, or are you trying to remove water that got into the cylinders or crankcase?

If you're trying to drain the coolant passages, Vince is correct. There is a plug on each side of the block near the bottom. If you are trying to drain the crankcase, just drain the oil and the coolant will come out with it. If you're concerned about the cylinders, when you remove the head you'll be able to dry them out.

If there is rust on the cylinder walls, I would first dry the, then wipe them down with a cloth soaked in penetrating oil. After that I would spray a generous amount of penetrating oil on the cylinder walls and turn the engine over by hand. If there is any pitting in the cylinder walls, you'll need to tear the engine down and rebuild it.

Dead Parrot · 05-22-2020, 05:12 PM

If you are a few days from starting work, not much to do at this point. If it is going to be a while longer, pull all the spark plugs, disable the ignition, disconnect power to the fuel pump or disconnect the suction side hose, spray a some WD-40 or similar into the cylinders and crank. Yes, it will make a mess. But it will get most of the coolant out of the cylinders. Lastly, squirt some non detergent 30w into the cylinders and crank some more. You want to coat the cylinder walls with a good coat of fresh oil.

I would replace the gaskets on both sides. If one blew, the other might not be far behind. Unless there is a lot of rust damage, replace the gaskets and run it. Even if it burns a little oil, it would take many gallons of oil to equal the machining cost if you pulled the motor and had it reworked.

05-22-2020, 12:13 PM	#1
daveccpa Registered User Join Date: Jun 2010 Location: Olympia, WA Posts: 37	blown head gasket My son blew a head gasket on his truck LT1 SBC 350. He's back at college so I'm trying to fix it for him. Any suggestions on flushing out the block of the water that got in it? We drained the block literrally right after the gasket blew and it's been sitting for a month now. I took the valve covers off and there is a bit of rust now on the inside of them. The valves look fine. Just trying to decide if I pull the whole motor and rebuild or just fix the gasket and go on. My son wants to replace the engine in a few years anyway so maybe its best to just replace the gasket and do what ever else to keep it running. __________________ 1959 GMC Fleetside Longbed

05-22-2020, 02:16 PM	#2
vince1 Registered User Join Date: Jan 2013 Location: Calgary Alberta Posts: 1,164	Re: blown head gasket Isn't there a plug at the bottom of the block to drain the water? I don't know if on one side or both. Taking off the lower rad hose should also drain most of it. Drain the oil and put in fresh before re-starting it.

05-22-2020, 02:43 PM	#3
truckster Senior Member Join Date: Jan 2001 Location: Orem, Utah Posts: 7,794	Re: blown head gasket Please clarify - are you trying to drain the coolant passages, or are you trying to remove water that got into the cylinders or crankcase? If you're trying to drain the coolant passages, Vince is correct. There is a plug on each side of the block near the bottom. If you are trying to drain the crankcase, just drain the oil and the coolant will come out with it. If you're concerned about the cylinders, when you remove the head you'll be able to dry them out. If there is rust on the cylinder walls, I would first dry the, then wipe them down with a cloth soaked in penetrating oil. After that I would spray a generous amount of penetrating oil on the cylinder walls and turn the engine over by hand. If there is any pitting in the cylinder walls, you'll need to tear the engine down and rebuild it. __________________ I have sworn upon the altar of God, eternal hostility against every form of tyranny over the mind of man. - Thomas Jefferson

05-22-2020, 05:12 PM	#4
Dead Parrot Registered User Join Date: Aug 2012 Location: Oklahoma City, OK Posts: 2,476	Re: blown head gasket If you are a few days from starting work, not much to do at this point. If it is going to be a while longer, pull all the spark plugs, disable the ignition, disconnect power to the fuel pump or disconnect the suction side hose, spray a some WD-40 or similar into the cylinders and crank. Yes, it will make a mess. But it will get most of the coolant out of the cylinders. Lastly, squirt some non detergent 30w into the cylinders and crank some more. You want to coat the cylinder walls with a good coat of fresh oil. I would replace the gaskets on both sides. If one blew, the other might not be far behind. Unless there is a lot of rust damage, replace the gaskets and run it. Even if it burns a little oil, it would take many gallons of oil to equal the machining cost if you pulled the motor and had it reworked.



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