Hey guys i’m very confused as to what is happening now, I have a 09 silverado 4.8l that broke down on the way home from work one day, long story short valves were leaking and heads were warped + blown head gasket, it does have a stage 2 summit racing cam and tune + supporting mods but that’s about it, I took the heads (243) to the machine shop and had them resurfaced, milled back 5 thousandths, and valves lapped. Long story short i put the new felpro head gaskets on and start it up, coolant starts mixing with the oil BIG time even with the engine off, so I tore it back apart to see if anything was wrong, forgot the dowel pins(i know rookie mistake) and i put them in, bought new felpro bolts and gaskets, got the heads torqued down and filled it with coolant, none mixing with oil and was holding it, start it up drive it around the yard and decided to drain the oil and put new oil in, with the drain plug out i started to pour coolant in and it starts coming straight out of the oil pan. I’m at a loss now and have no idea what to do, any help would be appreciated, thanks!

 

Maybe I'm wrong but it sounds like there's an inssue with the engine block. There's also the possibility of a damaged cylinder head or faulty water pump.

 

With the spark plugs out, add water to the cooling system and have somebody crank the engine over.... See which spark plug hole is shooting water out. That should give you a cylinder to focus on for the next steps.

Pull the heads.

Triple check your head gaskets that they are correct for the application, were installed correctly, etc.

Inspect each cylinder for a hairline crack.

Take the cylinder heads and have them pressure checked.

 

I’m starting to think it’s the engine block too, the heads were pressure and vacuum tested and held up and the water pump and thermostat is brand new! i’m just confused as to why it wouldn’t do it before it was started and now it will mix coolant and oil with it off!

 

The head gaskets are for sure the right ones, i got them from o riley’s and saw where the front goes etc. The heads were warped but milled back 5 thousandths and he said they were flat, they held up to the pressure test and were good there. I’m starting to think there may be something wrong with the block

 

sounds like bring it to a shop and have someone else actually fix it

 

Lol if i pull the 4.8 out it ain’t going back in, heads are good so i’m most likely gonna get a 5.3 or 6.0

 

Water can get from the cooling system to the crankcase without passing through the cylinders at all. IOW you can have a busted block (freezing for example) that will exchange water and oil butt the cyls still be perfectly intact. So all that about spark plugs and cyl wall cracks and heads and such is a waste of time: that can all test perfectly good, butt the block is still trash.

Sounds to me like your block is toast.

Time for a 6.0.

I see you're standing in the engine room there... that's how I work on mine alot too.

 

Does the radiator have an oil cooler built-in?

 

What turned out to be the issue? Toasted block or smth else?

 

No lol, it was something very stupid, took the heads off and had them pressure tested, somehow there was a crack connecting a water jacket to the oil passage on the heads that the machine shop didn’t see before. They replaced the head for free so that was a win!

 

Uhh... there are NO oil passages in the heads. All oil to the rockers travels thru the pushrods, then drains back to the lower end via pushrod holes.
To repeat, there are NO oil pressure passages in the heads.

 

I was going to guess cracked heads, but kept reading...

I'm glad OP found the problem. How or why did the truck overheat?

 

If they had been the 706 head casting, made by Castech, then cracks near the head bolt holes that leak coolant into the oil are VERY common. 243 casting isn't subject to that particular problem butt of course can crack in other ways, same as any other casting. As stated above, there are no "passages" for oil in the heads, unless you consider the drainback holes to be a "passage"; butt there's water on one side, and crankcase on the other, of the ENTIRE top of the casting under the valve cover.

Glad it was easy to resolve.

 

Che70velle mage a good post here, even though it didn't turn out to be the case this time. Those in-radiator-coolers, whether for trans fluid or engine oil, or both, can and have failed. It's not common, but it has happened. Repeating my earlier post here-If you have a case of slowly losing coolant, but there's no cross contamination, don't be to quick to dismiss the factory clamps. Especially if they are 20+ years old. I have never heard of anyone else besides me (figures!!) having a weak factory clamp cause a coolant leak, but I'm living proof it can happen......