how to test for cracked block - merc 3.0 LX

[CamaroMan]

Hi all - put this motor together - motor mixed water with oil after running first few minutes - long story, but how does one check whether a manifold or block is cracked? I have the dye spray cans. What are common crack areas for the 3.0 block and manifold and head??

What do these pics tell you? I have checked across the back of the block under the manifold for cracks but it looks good..

Its my understanding that water and oil can only mix via either the head or the block, not the manifold on these? Looks like the thing sat in the rain or something, why would ALL the intake ports be rusted. All cylinders had water and surface rust too-



How would I know what is bad, at first i thought head gasket but it doesnt look like it leaked thru anywhere, blocked was flat and head lightly surfaced before rebuild..

 

[Scott Danforth]

by looking at the head and ports, the exhaust was leaking into the cylinders.

 

[Bondo]

Ayuh,..... Peer into the intake runners, 'n follow the rust to where ever it ends,.....

Most common block crack spot on that motor is inside the crankcase, opposite the block's drain plug,.....

 

[CamaroMan]

by looking at the head and ports, the exhaust was leaking into the cylinders.

So would that possibly be a cracked manifold? How would water from manifold get to oil? Or could the head be the reason? The rust was from after the water and oil mixed ..

tx bonds, would that be visible from the outside? And opposite drain plug u mean inside by the drain plug or opposite by the lifter cover?

 

[Scott Danforth]

if you have a leaking manifold, the water leaksinto the exhaust ports, past the valves, sits in the chambers and leaks past the rings.

if the rust is from after running, then all 4 cylinders would be equally rusted.

another potential, is you ran the motor hot, and it spit the head gasket.

3.0's often crack on the inside if frozen.

 

[Scott Danforth]

either way, with the amount of rust you have in the jugs, your going to need a full rebuild. buying a used motor will be much cheaper

 

[Rick Stephens]

I don't know of any way to be sure you don't have cracks other than to reassemble and pressure test the cooling system. I kind of disagree with Scott on how there is so much rust that it can't be successfully rebuilt. That all looks like surface rust to me. I had worse from an open carburetor on a motor - had to bore it out, but it was same deal only left with water inside for a year. Your's doesn't look like pitting at all.

I disassembled my wet motor before realizing I needed to pressure test first. That I figured I knew the cause of water in my engine was not a good excuse. In your case, unless you

 

[Scott Danforth]

Rick,

its not a question of can it be rebuilt, because it can. the question is..... is it worth it?

with the $1000 to $1500 to rebuild the motor vs buying one for $300 or less. it is simply cheaper to buy a different running motor vs rebuilding it. I will take the $700-$1200 and buy beer and gas. plenty of running 3.0's sitting in free rotten hulls (including a 2002 bayliner near me). not worth even pulling the oil pan on a motor that has that much rust in the bores.

 

[fishrdan]

Agree with Bondo's post. Also, you can fill the manifold water jacket up with acetone and see if/where it's leaking. I think the manifold is shot.

How long has the water been sitting in the engine, fresh or saltwater?

 

[Rick Stephens]

Rick,

its not a question of can it be rebuilt, because it can. the question is..... is it worth it?

with the $1000 to $1500 to rebuild the motor vs buying one for $300 or less. it is simply cheaper to buy a different running motor vs rebuilding it. I will take the $700-$1200 and buy beer and gas. plenty of running 3.0's sitting in free rotten hulls (including a 2002 bayliner near me). not worth even pulling the oil pan on a motor that has that much rust in the bores.

I hear you. Looks like that motor was already rebuilt. Hence, if the issue was manifolds or head, where do you draw the line?

 

[Scott Danforth]

where do you draw the line?

When repair costs more than replacement

 

[fishrdan]

One thing i find quirky is that it looks like a fresh rebuilt, pistons clean, but they look to be marked "STD", which would mean the engine wasn't bored.... I guess the cylinders mic'ed within spec upon rebuild???

I'd atleast tear it down, run a hone through the cylinders "a bit" (not hogging it out or trying to remove pitting), then see how bad the cylinders are. Worst case - it's a boat anchor.

Actually, if it's a fresh rebuild, boring, new pistons and cleaning up the head may get it back together 100%. With that much rust, I'd guess the valve seats are pitted, head may need a valve job??? Well, that and a new manifold. Not a $300 used motor, but certainly cheaper than a "complete" rebuild.


I have a bit of pitting in my cylinders from a cracked manifold 4-5 years ago, was sitting for several (?) weeks with water in the cylinders. Meh... Tiny bit of blow-by due to the pitting, but it runs fine.