Long story, Ill make it as short as I can. I bought an '04 Tahoe 4x4 w/ the 5.3, 155k mi about 13mo ago - completely stock. Once I changed the oil a few times a pretty bad lifter tap appeared on cold starts, got worse pretty quickly. This gave me an excuse to rebuild the top end, and add a new cam/heads at about 172k mi. Over the 4th of July weekend I tore it down to replace the lifters w/ new LS7s, pushrods, BTR stage II cam, built 243 heads, all gaskets/hardware in between, and a dyno tune afterwards. I was a GM tech for 5 years and have done a few performance head/cam swaps on these engines in the past, so its a job I was very familiar with. Everything went pretty well until I got the front cover and valve covers off. This engine is hard sludged worse than almost any engine I've ever personally worked on. Looks like between the fuel dilution, probable long oil change intervals, an obvious overheat or two, and maybe some water entry from the previous owner, this bulletproof engine is in alot of trouble. I pushed on with the rebuild, cleaning everything as well as I could without a parts washer. Here are some pics pre-cleaning:





Note: I was not planning on replacing the oil pump or timing gear/chain at this point - I (somehow) had decent oil pressure before the rebuild and was going to do later when I had the oil pan off and/or was adding significantly more power. Oil pump was NOT disturbed so I didn't have to worry about the pickup tube falling off.

I double checked everything, put it all back together, and went for the initial engine startup. Got 0psi oil pressure after about 15sec, shut if off - crap, I guess the oil pickup tube fell off while I was manually turning the engine over or something? Whatever, time for a new pump and LS2 chain/sprocket I guess. I didn't have room to drop the diff and pan in my garage, and was short on time, so I had it towed to a shop close by. They found that the oil pan had about 1.25" of black sludge built up in the bottom of the pan, so between that and anything I may have dislodged during the job the oil pickup tube had clogged up completely - this got me worried because I know some had to get into the pump, but didn't think it would cause a massive issue. They installed the new pump, tube, and timing chain/sprocket, double checked all of my work and saw no other issues that would cause low pressure. When they started it, they only got 4psi oil pressure at idle. They cleaned out the oil pressure sensor, checked it with a mechanical gauge - still 4psi. At this point the mechanic and I assume sludge got moved through the system and probably clogged atleast one crank bearing or some other oil passage. I had him flush the hell out of it twice, once over the weekend - still 4psi on Monday morning.

So at this point, the bottom end needs a complete rebuild - something I don't have the time, tooling, or space to do myself - this is my DD. On top of that, the wife is getting very tired of my old truck habit, wants a K2xx Tahoe, and for me to stop buying NBS for DD duty. I really want to try to save it, its a great rig otherwise. What other options do I have? Anyone else here ran into anything like this? I am thinking of trying to just dump a gallon+ of B-12 Chemtool into the crank, letting it sit for a day or two, and turn it over by hand a few times. Good idea? What else would you folks do? Any help is much appreciated.

 

looks like coolant contamination in the oil, imo

its hard to say what might save it. Did you do a new pick up tube, or just cleaned the old one?

The oil cross over in the rear cove may be so clogged its preventing oil to the lifters and preventing drain back to the pan through the passenger side of the lifter valley, so thats something to check

could pop the pan off and pull rod caps and look for sludge in the crank as well

or could run it and let whatever is gonna happen, happen. LS1Tech says 4psi is enough to float the crank on these motors

 

Is that crossover accessible with the trans still installed? I've never messed with one of those. Yes, new pickup tube when they replaced the pump. When the shop had the pan off they looked as well as they could and said the crank had sludge all over the non-rotating parts they could see - so yeah I assume thats sludged as bad as everything else.

Thought about just dumping some 15w40 in it an letting it roll, but dont wanna ruin the top end performance parts I just bought and installed - I guess the heads would be okay, but I run a higher risk of trashing the cam/lifters/rods. Wish I woulda just put it back together once I saw the sludge and limped it along for another year or 2...

 

I had good luck with a high mileage used engine.

 

You would have to drop the trans and pull the rear cover to get to those passages and the crossover (crossover is machined into the cover)

 

I see no problem with removing your oil and dumping some B12 or something else in the crankcase. Remove the fuel pump fuse and stuff so it can't fire and just crank that stuff through the engine with the starter. Do that a couple times a day for 2 days, dump it out and put the oil back in. See if the pressure is better.

 

Mix it with some ATF and run it too

if its already looking like a rebuild, may as well

 

Good idea on pulling the fuel pump fuse. Ill probably give this a try and then move on to whatever i come up with next.

 

That stuff might disolve seals. Now that I understand the extent of what is going to happen to this engine to give it one last chance at life, let me add my $0.02 worth of flushing advice. I would put a gallon of diesel in the crankcase and a quart of ATF, and do FFDP's procedure. Except for maybe a week.

Diesel because kerosene is so expensive now.

 

Ended up just going with diesel and trans fluid, B-12 is apparently suspect to damaging seals on its own - its alright when diluted with engine oil while doing a normal flush. Also its $30 for a paint can worth. Turned it over without the pump relay a few times. Going to repeat a few times and give it until Sunday evening and see where that gets me.

I did crank it up earlier since it has some oil pressure. Was able to get it to about 20psi at 1500rpm, didn't take it up to operating temp though, still below spec but its movin' at least. Definite bottom end tick at idle, but not knocking. When i pulled the oil drain plug there was very minimal metal shavings on it, and it didn't smoke when running, its unlikely that its burning through a bearing at this point. Keeping my fingers, toes, and dicks crossed that this works - but I'm not expecting it to.