Merc 454 overheated and cracked block

"i need some serious help here

"i need some serious help here guys. i have a 1989 rinker with a chevy 454 . was running great until it overheated and mechanic changed the impeller , blew out hoses , cleaned out oil filter ( honeycomb had bits of impeller pieces in it) changed thermostat, checked thermostst housing, replaced port exhaust manifold , cleaned out risers .....still running at 160 and climbing to 185 with muffs on. at this point we are all baffled and still can't figure out why there was less water coming out of port side exhaust than on the other side. we checked head gasket ....all o.k. checked compression all 150 on each cylinder. finally took head off thinking there was a crack but instead we found a dark black line in #3 cylinder . mechanic tells me this is a crack between the water jacket and exhaust . he tells me to shop around for a new 454 block !!! i am really lost .i can't figure out how the rest of the internal parts of the engine are clean as hell and look new but a babied 454 cracks a block . is this common ? van overheating for 20 seconds cause this? is it really a cracked block ? HELP !!!!! ANYBODY PLEASE!!! IF TRUE WHERE TO FIND A BLOCK ???
ANYBODYS HELP WOULD BE GREAT ."

"Not that common. Is the crack

"Not that common. Is the crack in the bore straight or jagged? A crack in the bore will almost always be jagged and show rust (like you said... dark). Stright might be a scrape from a ring.

Cracks happen when you overheat engines, but the heads almost always let go before the blocks. Just my experience. Your water flow might be obstructed by trash in the block os something, btw.

If you’re sure about the diagnosis, I would simply buy a "short block" - replacement engine without the heads and bolt up your existing heads, manifolds and other peripherals. Go boating."

"OK I'm not following this

"OK I'm not following this but that doesn't mean much. You say you checked the head gasket an it was fine,then checked the compression an it was 150lbs on all cylinders. Then you removed the head & found this crack.

Ok here is where I get lost on this. I don't understand how you could check the head gasket without removing the head first.
Then if you had a crack between the water jacket & the cylinder wall how could you still have 150lbs of compression in that cylinder?
If the cylinder was cracked it would not carry 150lbs of compression.

On the cause of less water exiting the port side you say the port manifold was replaced. Just me but I'd take a close look at that manifold. For some reason it may not be passing the same amount of water as the old manifold did. Using muffs is not always the best way for testing the running temp of the engine,more so on a big block. There may not have been enough water pressure etc causing the high reading.
185 is really not out of line for being run on a hose. The thermostat could have a problem even if it is new.
If the temp never went over 185 I can't see a problem & a engine with a cracked block is not going to run smooth because that cylinder is not going to work with water in it.

I'd take a very close look at that mark in the cylinder wall & as Mr. Hays stated if the line is straight up & down I doubt the block is cracked.
The line could have been made from a piece of carbon or other type of material that was cought by the rings when the engine was running an cut a grove in the wall.
Unless for some reason cold water was able to enter the block at the time it was hot again I doubt the block cracked in a few seconds of running hot but then again crap happens.

I feel it is best to have this looked at by someone that is an expert in telling a cracked block from one that has a grove in the cylinder wall & with the price of a new engine on the line I sure wouldn't worry about hurting the feelings of the mechanic working on it by asking for another opinion.
There is a lot here that doesn't add up to a cracked block. But there is enough here to point to what could have been a problem with the new manifold all along.
Not seeing it for myself I can't really say but from what you said this is how I'd handle it.
Best of luck."

many thanks for your time in

many thanks for your time in replying .i will certainly follow your wise advice.
God bless

BY THE WAY GUYS THE APPARENT &

BY THE WAY GUYS THE APPARENT "CRACK" IS ABOUT 4 INCHES AND JAGGED ...IT IS NOT A STRAIGHT LINE AND HAS NO RUST LINES ...ONLY A BLACK SHADOWEY JAGGED LINES .... I WILL TRY AND FIND SOME EXPERT UP HERE ( VIRTUALLY IMPOSSIBLE IN MONTREAL) AND LET YOU GUYS KNOW THE RESULT .THANKS AGAIN TO DAVID HAYS AND CHARLI

Charli adds some great points.

Charli adds some great points. go get yourself a second opinion. The 150 compression point doesnt add up. Nor would the cracked block affect water flow.

".."could overheating for

".."could overheating for 20 seconds cause this?"

Most definitely! My Chrysler 360 rebuilt motor with less than 30 hours on it destroyed itself in less time than that when something plugged the water intake.

That's one of the hidden dangers of raw water cooled engines: Loose the cooling flow for 20 seconds and the block runs DRY of water. The result is near instantaneous overheating that wrecks the motor before your temp sensors or alarms go off (since these sensors DON'T work unless submerged in water). The paint was burned off the forward portions of the cylinder heads. You see an angled line across the heads where the water was gone (the motor sits at a 15 degree angle). And that sucker ran perfectly before that!

A FWC cooled system, like your car or truck, has a reservoir of coolant that has to boil away (taking heat with it) before the block is empty of coolant--a HUGE advantage.

I'm in the process of coming up with a sensor system that will sound an alarm if the water level in the block goes down--the old Chevy Vega used something like this in the radiator.

Jeff"

"jeff,
that's probably wh

"jeff,
that's probably what happened... when i opened the hatch white ,burnt-rubber (oil ) smell poured out for about 1 full minute . that badboy was probably fried at that point ... the question now is where to find a short block ????
thanks again"

"this was my 454 cracked water

"this was my 454 cracked water jacket photo of cracked 454 between cylinders

"this was freeze damage, motor

"this was freeze damage, motor ran, but had zero compression on # 3"

"Eli:

Had very good luck wi

"Eli:

Had very good luck with a company in New Jersey called Marine Power Engines (NOT Marine Power). Nice people to deal with, and their product has run great.

Jeff"

to all you super helpful peopl

to all you super helpful people that took the time to reply and assist MANY THANKS !!!!
i hope to be hearing from you all again....under better conditions of course ....but hey ain't that boating .... Thanks again to all