Hey guys, I've seen some pretty fantastic help on here, and now I need some myself. I'm new to the Blazer community and have a 2004 Blazer with the 4.3L and 253K miles. Recently bought it as a project car. Long story short, there has been oil and occasionally coolant leaking from the front of the engine. I determined that the intake gaskets were bad and needed to be replaced. I also did the valve covers.

I proceeded to take it apart to replace the gaskets. I did both upper and lower gaskets. I will admit, I was sloppy on a few things...for example I guesstimated on torque when putting it back together and didn't polish dirt and corrosion off of mating surfaces, just wiped with brake clean. Anywho, I get everything back together and connected, go to start the truck, and it wasn't able to start. When I held the key, it held very low rpm and would not start. Eventually, the engine locked up. After I pulled the dipstick, I saw a LOT of coolant in the oil pan and upon pulling spark plugs, found a crap ton of coolant in 4 of the 6 cylinders. After removed the coolant from cylinders, the engine spun again by hand, so it was hydrolocked. I removed all coolant and oil from the oil pan, and shockingly there was somehow a gallon of coolant in the oil pan.

I was baffled how this could happen...namely how coolant could get into the cylinders via a bad intake gasket job. I took everything apart for round 2, got some new gaskets, and did it all over again. This time, I made sure to get the proper tools needed in order to smooth the mating surfaces and torque the bolts correctly. When pulling it apart again and smoothing surfaces, I saw that there was some corrosion on the intake side of the front cooling ports. I blasted it off, and the surface is a little bit uneven (minor pitting in the aluminum), but I was told by a professional friend that it wasn't significant enough to cause an impact. Also, the gasket I had replaced looked perfect, the RTV looked perfect, and literally everything looked perfect. I should also note that I found coolant pools in the upper intake manifold as well, even though clearly no coolant should go through there. Cleaned everything, new gaskets, followed procedure EXACTLY, and put it all together.

Instead of filling the system up with $60 of coolant again and learning the hard way, I decided to rent a vacuum cooling system tester/filler. Hooked it up in place of the radiator cap, and turned on. Vacuum was fine at first, and radiator inlet and outlet hoses squeezed in like they should. Vacuum got stuck at 20 in/Hg, and wouldn't go higher. When I shut the air off, the cooling system slowly lost the vacuum and within about 20 to 30 seconds it was back at 0. There was a gurgling sound as air was going through some of the leftover coolant sitting in the lower radiator hose. I checked all hoses for cracks, I installed a new thermostat housing as well. Clearly the cooling system isn't holding pressure now when there were no problems before the LIM job, so I obviously suspect LIM.

Is this the same issue as round 1 when started it and it hydrolocked? Or is this a smaller leak but still one that threatens the engine's ability to run properly? I know I did these gaskets right this second time. Is there a problem with the actual intake itself? Or is this completely intake independent and some other external issue is causing this? I'd appreciate any insight anyone has. This thing has been killing me, and if im gonna take the intake off a 3rd time, I'm gonna make sure I have a reason to.

Thanks all,

Jon