350 Magnum Cracks

"Hi Folks,

I recently purch

"Hi Folks,

I recently purchased a 98 Mariah with a Mercruiser 350 Magnum (5.7) from a trusted source. While doing the season open maintenance I noticed a couple of hair lines about 2-3" in length. I scraped away what paint I could just to see if it might be just a paint defect but the lines are embedded in the block. The lines run front to back about an inch below the cylinder head in the middle of the block (water jacket area). My fear of course is these may be cracks in the block possibly due to poor winterization, which could lead to other component issues as well. My questions are;
How can I determine if these are in fact actually cracks and not just some casting, handling, or other kind of superficial mark?
Is there a test kit such as a magna-flux or facsimile that I can purchase to determine this?
Could they simply be handling marks form a jig used to install the engine at the factory?
Is it possible that even though there is no apparent leakage externally and no apparent contamination of engine oil, that it could still be cracked?
Is there anyone out there who would be able to recommend repairing as opposed to replacement?
If in fact they are cracks, should I insist on a PCM engine as a replacement or is there an alternative of equal quality?

Thanks in advance for your helpful advise!"

"They are cracks but might be

"They are cracks but might be just superficial; is there rust on them w/streaks running down the block? No? Then they were made after the engine was painted. If they are not rusty and/or leaking, I would run it and keep an eye on them. But first pressurize the block to 15 lbs. and see if it holds pressure. If it won't hold pressure there is something needing attention.

"I recently purchased...from a trusted source." Then immediately tell your trusted source about the cracks, how concerned you are about them and see what they say. What is a PCM engine?"

"Thanks for your quick respons

"Thanks for your quick response!
There were a few light rust stains running down the block below the areas. But if metal were exposed it could have been from water draining from above?? I will pressurize the block as you have advised. Any advise on where to tap into the block to pressurize?

I have told the seller about the apparent cracks. He believes they are superficial. I hope he's right!

PCM ( http://www.pcmengines.com/ ) Marine engine builder. I noticed somewhere in the forums here that they were reccomended if an engine needed to be replaced."

""it could have been from

""it could have been from water draining from above??" Not likely; the rust running down is a telltale sign of a cracked thru block.

If the engine is FWC closed cooling with antifreeze, just go to an auto parts store and use the radiator pressure devise--15 lbs. is enough. It should hold the pressure for at least 15-30 mins. Any drop at all is a leak.

If the engine is raw water cooled, disconnect the hoses to the exhaust mans. at the T'stat. Now disconnect the hoses at the risers and swing them around to the T'stat fittings you pulled the hoses off. Tighten securely. Remove the water inlet hose at the T'stat and attach one end of a bicycle innertube to it--cut it to a 10" length w/the fill valve in the center. The loose end can be rolled tight over a pencil and clamped tight. Add 15 lbs. of air to it. Connect a screw on tire air pressure gauge and leave it. Test for air leaks at all your connections with a bottle of water w/a few drops of liquid detergent. What ever pressure it shows to start should hold for 5-30 mins.

Spray the suspect cracks w/the soap solution. Any tiny bubbles that show is a crack thru."

I'll give that a try and I

I'll give that a try and I'll let you know what I found. Thanks for your great help!