Help...White Smoke after HG Change

[DevilDog]

So i have a 96 Yukon, 4X4, 5.7 Vortec, 250000 miles, daily driver 100 miles a day. Last Thursday while driving I noticed the check gauges light come on and saw that the temp was red zoned, never overheated before. I pulled over and turned it off and heard the gurgle, after cooling off I checked and the rad was only half full. Topped it off and drove it home another 10 miles with mid range temp. After cooling off I checked the rad which was half again but when running there was no flow. The last couple days has been spent changing the water pump, rad, HG's, and all upper gaskets, since I know that these are prone to going out on Vortecs. Topped everything off, new antifreeze (green not dexcool, never had dex cool in it since I have had it), oil change, new plugs, etc. After bleeding the air from the system and letting it idle for a bit for gaskets to set, took it for test drive, when pulling out of driveway, it started blowing white smoke like no tomorrow, now it blows it even when idling. there is no noticible coolant loss from anything I can see and havent had to add any at all. Any ideas are welcomed, Thanks.

 

[Mike_L]

I would expect some for a little while while it burns off the coolant that you probably spilled into the cylinders while doing the change. If it goes on for a long time then it could be something else.

 

[inthechateau]

If the HG blew and you were smoking prior to change i would expect some coolant in the exhaust system. I fyou are real concerned do a compression test on all cylinders. If they are close to even then you are buring coolant out of the exhaust system. I just did a 5.7 Tahoe and it took almost 30 minutes to clear out the system.

 

[DevilDog]

Ok thanks, I forgot to mention that it had never smoked prior to this incident, even after overheating, but HG on passenger side did show a bad spot. Also I did a comp test earlier today and had average of 120 across the board with no leak down. Hopefully its just in the exhaust, Ill take it for a good "country drive" tomorrow and see from there. Are the Vortec heads prone to cracking if overheated ? like in my case? Thanks again.

 

[retorq]

Did you get the heads checked for cracks and warpage?? Good chance since you maxed out the temp then drove it after that while it was still broke you broke it worse.

 

[DevilDog]

Did not have them checked by a shop, did acid dip them and clean them good then checked them with flat edge and feeler gauges, no noticible warpage on either one, also did a thorough check of all areas and no obvious cracks. short of magnafluxing them or pressure testing them no damage. But when I did the comp test there was no leak down. Thanks.

 

[inthechateau]

DD, keep an eye on the coolant level and for contamination in the oil. If your temp stays normal and smoke clears in a few miles you should be good to go. What did you do for valve last setting? I'm having problems getting mine to adjust.

 

[DevilDog]

so far no coolant / oil contamination and level good to go. Valve lash was set at zero lash and stop. Found out when I did this that these Vortecs are designed to run at zero lash and no more anything more holds valves open and thus no compression. Sounds sloppy but after about 5 mins runtime, she was purring. Slowly adjusted according to firing order until finger spin on pushrods stopped and that was it.

 

[SunlitComet]

The heads can crack from combution chamber temp but only micro cracks near the valve seat. Never seen a vortec head crack to leak coolant. And calve adjustment is simple.

 

[DevilDog]

Ok, thanks sunlit. Im going out there now to check and test everything again then go from there. Talked with a buddy last night who has a known good set of heads I can get if needed. But they are off an 89 model 350, and from what he says they are double humps. Thanks again.