losing coolant and lifters tapping

[Dpounders]

I recently purchased a 2005 GMC Yukon 5.3L with 172K. I noticed that the heat wasn't working but I found the coolant low, topped it off and it worked fine. However, it seems to be consistently losing coolant at a rate of about a 1/2 gallon per 800 miles. I changed the oil as soon as I purchased it a couple of weeks ago using NAPA 5W-30 and a NAPA Gold filter. This past weekend I went camping with our boy scout troop and towed their trailer about 300 miles mostly on the interstate. After getting home, the next morning I started it and there was what sounded like a lifter tapping for about 30 seconds and then started quieting down and was completely gone after about 45 seconds. The vehicle runs perfect and no sounds after that. If I shut the vehicle off and restart the tapping is not there. It's only when it sits for about 8 hours that it starts to tap again on cold starts. Weather is about 30-45 degrees in the mornings. Any ideas?

 

[ATL]

these motors are known for making tapping noise on cold startup, thats perfectly normal. but keep an eye on the coolant. try your best to find a wet spot on or around the motor. lets hope its leaking externally and its not a head gasket

 

[Dpounders]

I can't find any signs of leaking externally on the ground or the motor. However, I checked the oil and I don't see any sign of coolant there either (no cloudiness, bubbles, film, etc.).

 

[ATL]

when i had a head gasket go bad, the coolant didnt make it in the oil, but it made it in the cylinder everytime i turned it off. it would idle rough for 5-10 seconds on crank up and be fine. but take a look at the underside of your water pump

 

[Dpounders]

Yeah it definitely doesn't run rough on start up at just has the ticking/tapping sound for 45 seconds. Have you or anyone ever tried adding Lucas Heavy Duty Oil Stabilizer or anything similar to the oil to try to eliminate the ticking/tapping sound? Is it possible that the coolant could be causing this sound on startup somehow?

 

[ATL]

most of the time that sound is piston slap. its caused by the tolerance differences in the pistons and block. once they heat up alittle and swell, the sound goes away. you may have the aluminum block 5.3, its highly sought after motor but unfortunately the aluminum blocks have more piston slap than the iron blocks

 

[Dpounders]

If it was piston slap wouldn't the sound start appearing gradually and get louder. This motor was quiet and then all of a sudden started doing it.

 

[chauncey0337]

"Piston slap" happens mostly when the temp is cold. And like ATL said it's common on these trucks. I've heard replacing the oil pick up tube o ring can fix the slap. Whether it works or not, I don't know for sure. Also heard the 2 cycle oil treatment helps.

 

[M3PO]

Agreed, tapping sound is common.
The coolant consumption is something to check out, as mentioned before you could have a head gasket or other issues.

 

[ATL]

i dont believe there is a fix for the slap, its the tolerances. aluminum contracts and expands more than iron, thats why the aluminum blocks slap worse. as the aluminum is heated, it expands, tightening up the tolerances between piston and cylinder causing the slap to go away.

if the sound just started, i wouldnt assume it to be piston slap. but im wondering with it being a new vehicle, maybe its just something you never actually listened for. but after that oil change, the mechanic in you made you stop what your doing and listen to make sure everything was done correctly.