Hole in block!

[L124C]

I have a raw water (salt) cooled Yanmar 2GM that runs like a top. The other day I noticed some white powder forming on the top of the block. I then noticed steam coming out from this same area while the motor was running. It turns out there is a pin hole, in the block where the valve cover meets the block. I have a mechanic scheduled to take a look at it, However, I have to believe the diesel is toast.
How can the corrosion be so severe that it has eaten through the block, and yet, the engine runs great? It starts perfectly, has plenty of power, and has no symptoms of any problem (except for the steam, and salt!). This absolutely amazes me!
Why has the corrosion advanced to this point, though the internal motor zincs never seem to be attacked?

[SVDistantStar]

JB Weld..................

[Stillraining]

I Second the JB Weld...

I had a Case 680 Rubber tire Backhoe that cracked a block 12 or 15 years ago...It was maybe 3" long...that JB weld was intended to patch it up untill the job was finished...4 years later I sold the Machine...with full disclosure of course..

Truly an amassing product...Prep is the key

[SVDistantStar]

Yes, JB is the stuff. A buddy of mine has a jet-ski thats been patched up with JB on the block many times. It still runs and rides fine.

[sailaway21]

I'm guessing you've got a blown head gasket and it's fixable.

[Stillraining]

Sway he said he found a pin hole....

To answer your corrosion question...its called electrolysis...and yes it eats from the inside out...We have lost blocks in our equipment from just that...usually behind a liner...It is important to put into your system a inhibitor such as Nalcool 2000 or equivalent..

Originally Posted by sailaway21

I'm guessing you've got a blown head gasket and it's fixable.

[Rockter]

Guys, he cannot put inhibitors in there. the motor is raw water cooled.
L124C, can you post a wee picture on here so's we can see?

[L124C]

Originally Posted by sailaway21

I'm guessing you've got a blown head gasket and it's fixable.

For the record, it turns out Sailaway was almost correct. In fact, the first mechanic that looked at it thought it was the head gasket. The water pump gasket was the culprit. The hole I was looking at was nothing but some surface corrosion. Whew!!!

[Capnblu]

By the looks of the responses you got, I guess it would be a good time to encase your boat in JB WELD. It sounds like it can hold together everything. Like my Grandfather always says, "Don't let common sense or good judgement get in the way of someones bad idea."

[seabreeze_97]

I saw a NHRA Top Fuel (nitro-methane) finals race once where it turns out the winners were celebrating wildly. When they explained their jubilation, turns out they'd cracked a head in the previous run and were not able to do a swap, so they JB Welded it up. It held. Really amazing stuff.