Hello,
I've had 3 Suburbans previously and purchased this one last fall with 135,000 miles on it (2007 LTZ with LC9 motor) and this one has given me more problems than the other 3 combined. About a month ago after towing our boat it started acting different and I noticed at startup the dreaded white smoke for a while and it idled rough but hasn't had a check engine light on. After it warms up this all goes away and all is well. It's never held good oil pressure either- 20 at idle and 40 at speed. It has lost some coolant but none showing in the oil and no oil showing in the overflow. When accelerating you can hear water swooshing in the dash heater core. Last week it started showing overheating on the gauge but the infrared gun shows 180 degrees on the thermostat. To top it off it has now started intermittent lifter tapping sounds and it won't start until you bump it several times and then it starts like nothing is wrong. I have it scheduled to go in the shop next week and I'm wondering what route to go.
I'm guessing it has a cracked head or hopefully a cracked head gasket and coolant is leaking into one of the cylinders. I'm debating buying a junkyard motor with lower miles or replacing the heads/gasket. Sorry for the lengthy description but the list of symptoms is long. Thanks for any advise on this.

 

My Suburban has a junkyard 5.3 in it. Runs great. Been driving it for almost three years, every day. I suppose it always a bit of a gamble to put in a junkyard engine. Mine burns about a quart of oil between oil changes, lots of city driving. I call that a win.

BTW, I have heard a lot of complaints about the 2007 models specifically (Suburban, Tahoe, Yukon, Sierra, Silverado).