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Questions on the Castech #706 casting coolant leak problem?
Does the leak start only after the engine has been once over heated or do they just start leaking?
Is the “Genuine GM (122378255) Fluid cooling system seal tablets” a good preventative stop leak measure on a non-leaking #706 heads?
Should I keep my #706 non-leaking as of now heads or buy used #862 heads and overhaul them?
The reason I am asking is that my next mod is to do some head porting [valve seat to port blending and better the only-two angle stock seat angles] and checking the exhaust port to header size. Maybe increase the combustion ratio, and check the valve train geometry.
I can buy a pair of #862 casting heads at the local salvage yard for $175, either a 1999 or 2005 heads from 5.3 pickups. They are still on the blocks and will take a look before buying them.
I bought the 2002 truck new and now have 80,000 miles on it. I know that the #706 heads are the smoother SPM castings and flow better pre-porting than the sand cast #862s.
Thanks in advance for your input.
Last edited by Metalchipper; Mar 23, 2019 at 12:20 PM.
Reason: 607 should be 706
I noticed your remark above about doing exhaust port work according to header size. If the port is a bit smaller than the header, leave it as-is, as the difference will aid in anti-reversion of the exhaust pulses. I remember this from about 30 years ago. It seemed to help scavenge better
They just sort of randomly decide to start leaking when the spirit moves them. Bear in mind, the problem isn't "706 heads"; it's CASTECH 706 heads. Look carefully at their casting mark; if it looks kinda like a battery, they ARE Castech, and they WILL fail eventually. If it is NOT a battery, they do not have the problem. Ask The Google if you don't know what the mark looks like, it knows, and will quite likely offer you, among others, my photos of mine, which clearly show the gunk it turns the oil into, and the "steam-cleaned" looking area at the crack and the bolt next to it. They usually come up on the 1st page of images.
Mine (04 Av... duh) broke at about 140k miles.
I would not recommend messing with porting them, except MAYBE to smooth out any weird angles or steps right behind the valve seats where the factory jammed the cutter into them. Under no circumstances should you attempt to enlarge the ports, "gasket match", or any of the rest of that.
Likewise, I would NOT recommend ANY sealing additive in the cooling system, "Genuine GM" [get your filthy greeeezy 4-yr-old obsolete hooptie out of my NEW CAR DEALERSHIP shop] or any other. The risk of problems, like plugged heater cores and radiators, FAR outweighs ANY benefits. If there's a leeeeeek, FIX IT, and don't try to … ethnically engineer around it.
There's very little "check the valve train geometry" available on LS motors. Not that it wouldn't help, but, there's nothing you can do about it, or very little anyway.
Thanks RB04Av,
You have answered my main question, if over heating causes the heads to leak-crack.
Yes I have removed the valve covers and the "battery" is there, they are not yet leaking, maybe waiting for a long road trip to do so!
Yes the plan is not to gasket match or enlarge the ports that would slow the velocity down and hurt torque.
I plan on checking the wear pattern on the top of the valves and push rod length.
I will add the CASTECH 706 to the list, replaced rusted brake lines, fighting rocker panel and over the rear wheel well rust. [thinking about spraying ATF inside]. I have scraped and POD 15 the frame and sprayed inside the rocker panels and the dirt channel on top of the rear wheel wells.
I am not going to mention the cold start up pistons changing bore noise. At lest it runs great warmed up.
Thanks again
Happened to me too. Was driving down a BUSY city street, pulling a trailer upon which was sitting a freshly purchased LQ9; light turned red; I heard a slight "pop" under my seat, and the brake pedal went to the floor. Fortunately I was able to not hit anything.
A FULL STAINLESS SET of brake lines was $108 something. A direct replacement with the same crap was $76. IOW, GM risked everyone's life on the road, for about $5 at their cost level. Thanks GM.
Morning, I replaced all the brakes lines with plastic coated lines, before any leaks. I tried to sell them on another forum but had no takers.
Coming soon!! will have a clean set of Castech #706 heads for sale. But wait, order now and you received empty spray cans! Pretty red rust
They just sort of randomly decide to start leaking when the spirit moves them. Bear in mind, the problem isn't "706 heads"; it's CASTECH 706 heads. Look carefully at their casting mark; if it looks kinda like a battery, they ARE Castech, and they WILL fail eventually. If it is NOT a battery, they do not have the problem. Ask The Google if you don't know what the mark looks like, it knows, and will quite likely offer you, among others, my photos of mine, which clearly show the gunk it turns the oil into, and the "steam-cleaned" looking area at the crack and the bolt next to it. They usually come up on the 1st page of images.
Mine (04 Av... duh) broke at about 140k miles.
I would not recommend messing with porting them, except MAYBE to smooth out any weird angles or steps right behind the valve seats where the factory jammed the cutter into them. Under no circumstances should you attempt to enlarge the ports, "gasket match", or any of the rest of that.
Likewise, I would NOT recommend ANY sealing additive in the cooling system, "Genuine GM" [get your filthy greeeezy 4-yr-old obsolete hooptie out of my NEW CAR DEALERSHIP shop] or any other. The risk of problems, like plugged heater cores and radiators, FAR outweighs ANY benefits. If there's a leeeeeek, FIX IT, and don't try to … ethnically engineer around it.
There's very little "check the valve train geometry" available on LS motors. Not that it wouldn't help, but, there's nothing you can do about it, or very little anyway.
Hello 86CAMARO400H,
No the 243 heads are good. It was only the CASTECH #706 heads that crack.
The 243 heads with the larger intake valves flow higher at higher RPMs. But the compression ratio suffers and low end torque on the truck 5.3 and the intake combustion area have to be un-shrouded.
243/799's are on every Gen IV 5.3 and 4.8, running either flat tops with 9.9:1 compression, or 3cc valve reliefs with 9.6:1 compression. Compression is not a problem with the right pistons.
OK, thanks.
I guess I got side tracked from my original question, sorry for the confusion on my part.
I was asking if I should keep my Castech #706 heads or go to #862s. Mine are not leaking but only have 80,000 miles on them, so if I do some mild porting-valve seat upgrades if now is the time to work on some different heads.
Some day I might go into the block to get rid of the cold start up knock but not yet.
Yes that is the Castech logo,
But I have the Castech #706 heads.
I am planning on looking at some #862s on a 5.3 2005 Chevy pickup [mine is a 2002 5.3 should should work?] tomorrow at a local junk yard --cost $175.
They are still on the block-truck. Going to ask how much they will take off the price it I pull them my self.
Then I can port-valve job-mill etc and not tie up the truck for that period.
Just posted it so you for sure know what to look for. Didn't know if you did or not and it can help other people that see the thread and have the same question.
Thanks 00pooterss,
No problem, I kind of thought that but it gave me a chance to rattle on a bit!
I have also seen a square Castech logo on the heads.
My heads might be OK, but once a year I take a 3000 mile trip and would hate to have trouble on the road. In January 2018 I had to drive the last 400 miles home in 2nd gear at 40 mph because a broken tranny cooler hose clamp broke and I lost all the ATF.
I will stop rattling on now.
Thanks 00pooterss,
No problem, I kind of thought that but it gave me a chance to rattle on a bit!
I have also seen a square Castech logo on the heads.
My heads might be OK, but once a year I take a 3000 mile trip and would hate to have trouble on the road. In January 2018 I had to drive the last 400 miles home in 2nd gear at 40 mph because a broken tranny cooler hose clamp broke and I lost all the ATF.
I will stop rattling on now.
LOL, to be honest, you probably know more about the castech thing at this point than I do. I just googled an image in case it helped.
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Castech #706 Keep or junk them? 
