5.7 Hydrolocked. Time for a new engine?

RedDirtErik

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Feb 3, 2016
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I've got a 1990 Galaxie ski boat with a 5.7 in it. First year I had it on the water, did great. We ended up getting a very early freeze that year and it wasn't winterized and cracked both sides of the exhaust. Replaced all of the exhaust and risers, took it out on the water and it ran great for a bit (about 3 - 5 minutes), then got more and more sluggish before dying completely. Got it out, looked it over and realized there was water in the oil. I can still bar the motor over manually. Haven't done anything with it since, trying to figure out the best way of diagnosing the problem and what steps I should take.
 

bruceb58

Supreme Mariner
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Mar 5, 2006
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30,454
You need to pressure test the cooling passages of the engine block. When your manifolds froze and cracked, your block likely did too.
 

RedDirtErik

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Feb 3, 2016
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I know the process on a radiator system, is it basically the same? I'm seeing GM crate motors for around 1500, sounds like it might be worth the investment at this point
 

Scott Danforth

Grumpy Vintage Moderator still playing with boats
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Jul 23, 2011
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I would read the stickies at the top of the forums for DIY things like winterizing.

regarding the motor, I would personally build a motor vs buying a crate motor. remember, boat motors are slightly different than truck motors. if your on a buget, you can get away with a long block from the salvage yard without rebuilding for about $300. you can build a stock stoke 350 for about $1500, and a 383 stroker for about $1800

if you get a standard crate motor, the minimum you need to do is pull the heads, change the head gaskets to marine, then replace all the steel core plugs with brass. I would recommend a marine grind on the cam as well.

remember to reuse your existing marine accessories and ignition.
 

tpenfield

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Jul 18, 2011
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I'd be leaning towards a new engine at this point, since the repair was so short lived. Probably some internal crack in the block that went along with the manifold freeze.
 

HT32BSX115

Supreme Mariner
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Dec 8, 2005
Messages
10,083
Got it out, looked it over and realized there was water in the oil. I can still bar the motor over manually. Haven't done anything with it since, trying to figure out the best way of diagnosing the problem and what steps I should take.

Howdy, Welcome Aboard!

The block is cracked. Pull the drive, pull the engine.

Remove all the marine "stuff", find yourself a wrecking yard 5.7 out of a similar year GM pickup and swap the Marine "Stuff" to it.

Otherwise, buy yourself a crate engine or a marine longblock.

Sorry about that,


Rick
 

Mercruiser420

Petty Officer 3rd Class
Joined
Nov 24, 2015
Messages
92
Hi,

Sometimes aftermarket manifolds/risers/gaskets don't fit perfectly...I'd double check that before assuming the block/head(s) are cracked.
 

HT32BSX115

Supreme Mariner
Joined
Dec 8, 2005
Messages
10,083
Hi,

Sometimes aftermarket manifolds/risers/gaskets don't fit perfectly...I'd double check that before assuming the block/head(s) are cracked.

Got it out, looked it over and realized there was water in the oil.
There just isn't a "big" path from the risers or manifolds that willl put huge amounts of water into the oil. It's on the order of table spoon amounts and it's only during shutdown. While the engine is running, the water goes out with the exhaust. If you run the engine long enough, pretty much all the water from a previous shutdown evaporates out of the oil.

The OP should of course isolate the manifolds and risers from the cooling system and do a pressure check of the block and heads to verify the leak. But, anytime you crack manifolds from freezing, the block is likely cracked too (unless it was drained) .
 
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