Hey there

i had a newly rebuilt 700sci. Put it in boat ran without water for 10 seconds engine ran well.

Put the belt for water pump on, connected hose. After two minutes engine hydro locked.

was shocked.

Coolant reservoir empty.

Opening engine Sunday. Would you think it’s from intake , head gasket, or somewhere else.

pressure tested manifolds all is good. they are brand new hardins.

thank you

Forgot to mention

water mostly in two cylinders

Which two cylinders? Rear? Adjacent?

if I’m looking at engine (belt) it is first two on the right side

1 & 3......Id be hunting down the guy who rebuilt it, have you contacted them ? could be head gasket or intake

Was it fresh water or antifreeze that filled the cylinders? Because you said coolant reservoir was empty, but you tested your manifolds?? The coolant reservoir is antifreeze, and the manifolds are raw water.

I had an engine a couple years ago that would start and run with no hose, but then as soon as a hose was connected it would quit. Ended up being a leaking intercooler.

Just went through this same thing at rebuild. The heads are BAD. There is internal corrosion in aluminum BBC heads due to sea water cooling. The heads should have been inspected before working on them. My heads were to the point of trashing them or welding them up around the water passages. It was $1000 to weld them to save them for another year or two.

Long story short the heads/ head gasket is leaking coolant. Weld or replace the heads.

LB4 the 700 SCI is closed cooled like the 525 and 600....so no acid water to deal with

Your Right, my mistake. Still the leak points to heads and head gasket issues.

Builder or owner put the intake on ?