706 heads
On The Tree
Joined: Oct 2011
Posts: 102
Likes: 0
From: Dirty South
Whoa Nellie what makes you think these heads are bad . Just because they are castech does not necessarily make them bad . First have done a visual check in the areas prone to crack . Then take to a good machine shop and have checked . The bad ones were in later years most of time ! If turn out to be bad get some 862s
TECH Addict
Joined: Dec 2017
Posts: 2,180
Likes: 969
If they aren't broke, they're fine, as-is.
The place they crack, is right below the center-most 3 head bolts. You can look at the area around those bolts (take off the rockers to see down in there) and it'll look steam-cleaned, might even have visible droplets of coolant sitting there. Bottom line, they leak AF into the oil.
If you run the green stuff, ... your oil will turn into something powdery and not oily, and your main & rod bearings will dissolve quickly. You'll know.
If you're using the orange, it'll blow a YUUUUUUJJJJJE puff of smoke at startup after it's been cruising for awhile, the inside of the oil fill cap will look like it has some kind of optional body fluid all up in it, the oil will be kinda black and thick-looking, and the oil pressure will drop quickly after putting in a new filter and then come back for a few hundred miles if you change the filter.
People also say that 799/243 off of a later-model (07? up.. not completely sure the year) 5.3 are a good substitute but I've never done that so I can neither confirm nor deny.
The place they crack, is right below the center-most 3 head bolts. You can look at the area around those bolts (take off the rockers to see down in there) and it'll look steam-cleaned, might even have visible droplets of coolant sitting there. Bottom line, they leak AF into the oil.
If you run the green stuff, ... your oil will turn into something powdery and not oily, and your main & rod bearings will dissolve quickly. You'll know.
If you're using the orange, it'll blow a YUUUUUUJJJJJE puff of smoke at startup after it's been cruising for awhile, the inside of the oil fill cap will look like it has some kind of optional body fluid all up in it, the oil will be kinda black and thick-looking, and the oil pressure will drop quickly after putting in a new filter and then come back for a few hundred miles if you change the filter.
People also say that 799/243 off of a later-model (07? up.. not completely sure the year) 5.3 are a good substitute but I've never done that so I can neither confirm nor deny.
Thread Starter
Teching In
Joined: Feb 2018
Posts: 3
Likes: 0
Restricted User
Joined: Mar 2014
Posts: 7,192
Likes: 109
From: Ohio
Any 706/862 head. Not all of them are Castech.
The number of heads cast by Castech is astronomical. Even if 1000 706 heads have cracked, its still a VERY VERY small % of them and you shouldn't worry.
The number of heads cast by Castech is astronomical. Even if 1000 706 heads have cracked, its still a VERY VERY small % of them and you shouldn't worry.
TECH Addict
Joined: Dec 2017
Posts: 2,180
Likes: 969
That's not true.
Cracked Castech heads are LEGENDARY. As far as I've been able to tell, probably a quarter of them in the 01 - 04 range at least, came from Castech; and of those, probably at least half with over 150k miles have cracked. And of course that's "old GM" so "new GM" won't do a damn thing about it.
I just replaced the 2nd set on my Av this past weekend. I should have gone with later-model ones but these were warranty, after being welded up in all the vulnerable places. But one of them cracked again in 2 spots anyway.
Cracked Castech heads are LEGENDARY. As far as I've been able to tell, probably a quarter of them in the 01 - 04 range at least, came from Castech; and of those, probably at least half with over 150k miles have cracked. And of course that's "old GM" so "new GM" won't do a damn thing about it.
I just replaced the 2nd set on my Av this past weekend. I should have gone with later-model ones but these were warranty, after being welded up in all the vulnerable places. But one of them cracked again in 2 spots anyway.
Restricted User
Joined: Mar 2014
Posts: 7,192
Likes: 109
From: Ohio
That's not true.
Cracked Castech heads are LEGENDARY. As far as I've been able to tell, probably a quarter of them in the 01 - 04 range at least, came from Castech; and of those, probably at least half with over 150k miles have cracked. And of course that's "old GM" so "new GM" won't do a damn thing about it.
I just replaced the 2nd set on my Av this past weekend. I should have gone with later-model ones but these were warranty, after being welded up in all the vulnerable places. But one of them cracked again in 2 spots anyway.
Cracked Castech heads are LEGENDARY. As far as I've been able to tell, probably a quarter of them in the 01 - 04 range at least, came from Castech; and of those, probably at least half with over 150k miles have cracked. And of course that's "old GM" so "new GM" won't do a damn thing about it.
I just replaced the 2nd set on my Av this past weekend. I should have gone with later-model ones but these were warranty, after being welded up in all the vulnerable places. But one of them cracked again in 2 spots anyway.
TOTAL bs.
Trending Topics
TECH Addict
Joined: Dec 2017
Posts: 2,180
Likes: 969
You apparently haven't ever hung out on any truck forums. You'd evidently be amazed to actually LEARN something, and find out how common the problem REALLY is.
An estimate of 1/8 of all trucks in that era equipped with 4.8 or 5.3 having experienced this, is probably on the low side.
An estimate of 1/8 of all trucks in that era equipped with 4.8 or 5.3 having experienced this, is probably on the low side.
LS1 Tech Stories
The Best V8 Stories One Small Block at Time
6 Common C5 Corvette Failures and What's Involved In Repairing Them
Pouria Savadkouei
Retro Modern Bandit Pontiac Trans AM Comes With Burt Reynolds' Autograph
Verdad Gallardo
Top 10 Greatest Cadillac V Series Performance Models Ever, Ranked
Pouria Savadkouei
Top 10 Most Powerful Chevy Trucks Ever Made!
Hennessey's New Supercharged Silverado ZR2 Has 700 HP
Verdad Gallardo
Coachbuilt N2A Anteros Is an LS2-Powered C6 Corvette In Italian Clothes
Verdad Gallardo
Awesome K5 Blazer Restomod Comes With C7 Corvette Power
Verdad Gallardo
10 Camaros You Should Never Buy
10 LS Engine Myths That Refuse to Die
Verdad Gallardo
TECH Addict
Joined: Aug 2005
Posts: 2,305
Likes: 126
From: Monroe,NY
Think about how many 706 castech heads are out there on millions of trucks and suv's that don't go on forums. I never heard of the cracked head problem until i went on this site. And the one thing you get on forums more than anything are the complaints.
TECH Addict
Joined: Dec 2017
Posts: 2,180
Likes: 969
a 5.3 will fit
"Beat" doesn't really seem to have anything to do with the Castech failure... it's more of just a thin place near the bolts that cracks from heat cycles or the like. Seems like somewhere around 125 - 150k miles is when they let go, if you have ones that are destined to fail.
BTW the later heads have a larger chamber. Those 5.3s have flat-top pistons whereas the earlier have dish. So they're not really a direct bolt-up option.