Well, i am at fault. Might of ruined my engine just for "giving it a try".
I had a very small leak in my radiator where i had to top off every friday. So, it wasnt bad. I heard of this stop leak that could possible stop the leak for good, or atleast until you get around to buying a radiator and installing it.
Friday before heading home from work i poured a bit more than half a bottle of Bars Leaks into my radiator reservoir and followed instructions. I live about 24 min away. Close to home i come to a stop sign and the dash start pinging. "low oil pressure" Shut off engine. Never seen that before. The engine sounds fine.
I make it home which i was about 5 min away or less. I park and my water level is fine and i check my oil and its also good. A bit under half mark. I top it off and again, at idle i get the low oil pressure on the dash.
I dump the oil and there it was..... i used the copper Bars Leaks. Well my oil was coming out super sparkly. Matching the Barks Leaks color.
After 2 oil changes and using liquid molly engine flush to try and clean out the engine still no luck on getting rid of that P0521 code. I got a new sensor installed. i flushed my whole cooling system. The BarsLeaks only last 30 min at the most, in my cooling system (and engine i assume) so it never really made sludge.
Ive always used M1 filters and Mobile 1 Dexos. Did something clogg up in there? I am picking up an oil pressure gauge at Harbor Freight right after this to test my pressure at the sensor.
I wanted to make a post about this because i cannot find anything online about this specific truck/engine. Now, the engine is well. Im hoping with one more oil change i can clean it up to where the code goes away? Sorry about how long this is. Any opinions and guidance will help. Thanks!
Hope to get some guidance.

 

I have never used bars leaks before, but there was a few times that I've used AC delco cooling system tabs with good luck, but anymore I just don't use any kind of oil or coolant additives. I get it fixed right. These newer vehicles cost way too much money to be messing around...lol.

 

Learned the hard way.
To my understanding the only way coolant and oil can mis is at the head gaskets. Does this mean that i blew one? coolant level never went down when my low oil pressure warning light came on. Oil level never went up either. Would be rare if only the the stop leak went through. But that is what might have happened? I am very confused. Im trying to find out where else could have coolant and oil mix other than at the head gasket.

ive done 2 oil changes as of now. and flushed the radiator couple of times. Still no smoke at the pipes which is great. The truck still drives about half a mile then gives me the low pressure oil on the dash.

 

I've used the Bars stop leak once or twice before, without issue, for minor coolant leaks on old cars.

Sounds like in your case though, coolant was not leaking externally, but into the engine oil, for the stop leak to make it into the oil pan. Or leaking both ways.

That could be a head gasket, but could also be the intake manifold gasket. I've had to replace the intake manifold gasket on my 1996 C1500 twice over the years due to coolant leaks. I don't hear of the failure as often on the 5.3L Vortec engines as those early 5.0 and 5.7 Vortec V8's, but am sure it happens. If I had to put money on which one failed, I would bet on the intake manifold gasket first. And if you have low oil pressure, that could be due to a blown section of the gasket causing a reduction in oil pressure - either to the outside (should see a leak), or over to the coolant.

If you had stop leak in the oil, do you also have oil in your coolant? I would look at that too.

 

Radiator had a micro crack. It would be a couple of drops every time i parked it. I mean, the stop leak worked as it stopped leaking but gave me bigger problems now.

I installed a Cold air intake a month ago and been getting a "check your air intake" message. I checked for leaks and everything is nice and snug. Dont think that had anything to do with it because the truck has been working great. Contacted Tuners and they told me for a simple plug n play, i shouldnt be getting that message there must be a leak somewhere.

With that said, does oil and coolant flow through the manifold where they could both mix?

The coolant comes out clean. So the leak is into the oil not into the coolant. it doesnt go both ways. Since the first time i changed the coolant it has never had oil in it.
The oil also doesnt have coolant it just has Stop leak.
My theory is that the stop leak is thick to where only the stop leak got sucked in? I did step on it to get into the highway 20 min after i put in the stop leak.

 

By the wat this is a ECOTEC3 engine not much difference but there are some.