I have an 05 cc z71 Silverado, VIN T. It succumbed to the Castech cracking issue a while back. Those original heads were 706's. I got a set of 862 heads from a local head reman shop who was familiar with the issue and installed them. Fast forward 2 years and now it seems at least one of the 862 heads has cracked. I looked up the TSB again and I noticed that it doesn't discern between casting numbers. It only calls out make, model, year, engine size and casting manufacturer. From what I've read, the prevailing opinion is that as long as you don't have 706 heads, you're good. However, my recent experience leads me to believe otherwise and the TSB seems to agree. Anyone ever seen a non-706 head crack like this?

 

Yes, from incorrect torquing.

 

Both the 706 and 862 castings are problematic. I would look into a 241 243 799 or 317 when you replace them to ensure a good casting. It seems like it is just a luck of the draw on the 862 and 706. If we can help you with any castings stock or aftermarket give us a call.
Thank you,
Kyle
972-853-2450
Thompson Motorsports

 

Almost all the GM heads including the 243's have the castech Logo. The 706 and 862 heads are cast differently using different process. It seemed to be more common that the 706 style of casting had more porosity were the casting joints were located. If you look at the casting it self though, there actually a nicer casting with less core shift.

The other cause would be cooling system maintenance. Examples include;

Not using Distilled water with Coolant instead of Tap water. Tap water has a lot of impurities, especially in farm area's or were well water is used.

Improper mix ratio.

Not replacing the Thermostat after a head failure.

Contaminated cooling system not being flushed out.

Not maintaining the coolant quality. If you read the fine print they usually want you to at least check it once a year.

 

Looking at swapping my 4.8 for a 5.3-woul having the donor computer help

 

Yes ive personally dealt with 2 set of 862 heads that are cracked and or porous around the head bolt holes. Ive still got one set of them on a 5.3l out in my shop, the other set got thrown away years ago after i swapped them out on the wifes o2 tahoe.

 

Personally I've come away good with 706 heads, actually when the first usage of coolant was due to my replacing red coolant with green. the 706s I'm running now no issues. Apparently its all about cooling system maintenance(preach to self) and correct torqueing. No experience with 862s...............