: how to avoid cracked heads?

02-03-04, 01:10 AM
Just some pointers is all im looking for.

02-03-04, 01:06 PM
Since when were "cracked heads" something to be concerned about....??? They seldom if ever crack.

If you wanted to avoid cracked heads on the Northstar engine (or any aluminum head engine) change the coolant frequently to assure that the corrosion inhibitors in the coolant are costantly replenished. Most situations involving "cracked" heads result from inadequate corrosin protection causing pitting in the water jacket area of the head and a resulting crack from the stress riser forming from the pit.

Aluminum heads exibit a corrosion problem called "hot transport deposition corrosion"... tiny bits of aluminum at a hot surface actually break away from the surface being heated in the presence of a corrosive atmosphere. The tiny (microscopic) pieces or bits travel in suspension thru the corrosive atmosphere and are deposited on the coldest surface they come in contact with. Applying this to the engine....the back side of the exhaust port wall is the hottest area. Depleted (old, non-corrosion inhibited coolant) coolant serves as the "corrosive atmosphere". The microscopic bits of aluminum break away from the back side of the exhaust port wall and travel in suspension thru the coolant and are deposited in the radiator...the coldest spot in the system. The pitting gets worse and worse until the pit becomes large enough to form a stress riser and the metal cracks due to thermal stress. Now you have a cracked head causing coolant in the exhaust and the radiator is likely plugged up with aluminum oxide.

This is a doomsday scenario. Hard to duplicate on an engine in the field unless the coolant is just run forever and the engine is run really really hard. Happens in racing engines all the time if the coolant is plain water with no corrosion inhibitors at all and the engine is run WOT all the time.

Changing the coolant frequently keeps the corrosion inhibitors up to strength and prevents this scenario. Since you are keeping the corrosion inhibitors up to snuff anyway to protect the head gaskets from corroding (the steel core of the head gasket can corrode from the inside out and loose strength) the issue of head cracking is way behind the issue of the head gaskets failing if the coolant is not maintained.

02-03-04, 02:40 PM
WHOA! you really know what your talking about! thanks for the info!