Am I In Trouble? Coolant Leak

[Crimson Nape Racing]

our 97 528 (80k miles) overheated in the spring when the water pump broke. My wife noticed it on a short trip (less than 4 miles), so I thought all would be ok. I took it to the shop on a trailer and had the entire cooling system replaced. Last week we noticed a smell and the attached pic is what I found when I looked under the car. The leak appears to be coming from the back passenger side of the engine between the head & the block. The car has only lost about 2 cups of water in 6 months, so it is a slow leak, and there is no water in the oil. I assume we have a warped head, but I have not heard of head warping and not leaking into the oil. What do you guys think, am I in trouble?

[JhwShark]

You are leaking out a freeze plug on the block. The cause is questionable...probably/definitely not caused by a warped head!

If you look on the side of an engine block you will see a line of circular depressions about an inch and a half in diameter and about a quarter of an inch deep. These are actually holes in the side of the engine block which are plugged with a dish shaped metal plug called a "freeze plug" or "expansion plug".

WHAT FREEZE PLUGS DO
As with many things on a car, there is an "official reason" and a "REAL" reason for freeze plugs. The official reason (and the source of the name) is this: If you run just water with no antifreeze in your car the water can freeze. When water freezes, it expands. If water freezes inside your engine block, it can expand and crack the block, destroying the motor. Freeze plugs (or expansion plugs) will "pop out" and supposedly prevent this. In reality this doesn't work all the time: I've seen MANY blocks destroyed by cracking without the freeze plugs popping out, or if they do pop out the block cracks anyway.

THE REAL PURPOSE OF FREEZE PLUGS
Engines are "sand cast". A special type of sand is poured into a pair of boxes. A "die" is pressed into the sand, making an impression of the engine block to be cast. The sections of the mold are then put together and molten iron is poured in, forming the engine. This is why engines have a rough texture on most areas: this is the texture of the sand used to cast them.

There have to be "cylinders" made of sand in the middle of this mold to create the cylinders of the engine block. These chunks of sand can't just "float" inside the mold: SOMETHING has to hold them in place. There are little columns of sand that connect the cylinder mold to the outer mold half. The mold for the cylinder "sits" on top of these. After the block is cast, these holes are machined smooth and a "freeze plug" is put in to plug the hole.

REPAIR/REPLACE
If the leak is slow and small, a stop leak or block seal compound might work, the right type for engine steel or aluminium! Of course, as with any "rig" of this sort, it might not work, might not last for long, and could clog up something else in your cooling system. The right way to fix it is to replace the freeze plug.

Best of luck,
Jon

[Crimson Nape Racing]

I should have said in the OP, but the leak is above the freeze plug. It's hard to tell in the pic, but it is definitely leaking from the passenger side rear corner of the head. I talked to 3 different shops, and they all said it is rare for just the head gasket to corrode. Most likely a warped head which means the fix will cost almost as much as the car is worth. We'll probably try to sell it as is and move on.

[Jeron]

It looks like it may be leaking at the freeze plug and the head.

If you R&R the head yourself its not more than the car is worth, $700-1500.

[Manolito]

On a 13 year old straight six, it is not unheard of for a head gasket to simply let go from so many thermal cycles. It becomes common after about 18 years. If you are sure that the leak is coming from the head gasket, I would give better than even odds that all it needs is gaskets. A shop will never promise you that, of course, because they want you to be prepared for the worst before they start opening things up.