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I have a S10 with a 5.3 in it with a 140K on it. It runs well but is leaking coolant on both heads after a drive. I put a few of those GM coolant pellets they first used on the Northstar engines and it stopped but I don't trust it. The heads are 706 Castech and they are known for cracking, there are bulletins on them, I don't feel confident even though the leaks stopped so I am going to pull the heads and get remanufactured ones (who is a reputable machine shop supplier for the heads) not just someone that is just going to hot tank them and do a valve job and send them out.
This is also a two part post. While the engine is apart I am going to install a Brian Tooley Truck Norris cam just for a little rumble and low end torque. I'm a old guy that does not race or drive stupid and never goes over 6K rpm. My second question is breaking in a new roller cam on a 140K engine. I use Mobil 1 full synthedic 5w-30 now. I read you don't need a break oil or period for roller lifters as long as they are in good condition. If I use the standard oil for flat tappet cam will this help or possibilly cause a oil comsumption issue. These two problems are driving me crazy and not sure what to do. I know there are a lot of smart guys out there that know what to do. Any help would be appreciated. Thank you and have a good day.
The Castech head problem is cracks under the valve covers right next to certain of the head bolts. It doesn't so much "leak", as such; it contaminates the oil. Eeeeezzzy to spot if you take off the rockers. It shows up as steam-cleaned head bolt(s), foamy stuff in the valve covers, black sludge all over everything else, milky oil that doesn't really look or feel much like oil anymore (more like mud), and oil smoke at startup. All of which is NOT saying, you should keep the heads you have now; just, if you get others, make sure they've been welded up at those spots. Repaired heads are generally more reliable than uncracked ones.
Note that all this applies ONLY to 706s cast by Castech. Not 862. There are 706 castings made elsewhere that don't have this problem. Castech's mark is toward the "right" side of the head (front of the pass side, rear driver's side) under the rocker shaft. Looks kinda like a D cell battery.
Roller cams require no break-in of any kind. Just use the same oil you are using now, which seems like a reasonable choice to me. It even agrees with what's printed on the fill cap.
Do yourself a favor for the long run. With 140,000 miles on them, buy a new set of lifters and trays. Buy the trays at the Chevy dealer, and make sure they have the GM part# on them.
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Coolant Leak and New Cam 
