EXTERNAL COOLANT LEAK BETWEEN HEADS AND BLOCK!!

[kuhio]

Ok, I'm sure this has been addressed in a previous thread but I'm lazy to track it down.....

1) I currently have about 15k miles on my TBI 350 rebuild, bored .030 over with new dart vortec heads. After installing and logging about 1k miles on the motor and collaborating with the engine builder in fixing some oil leaks in the oil pan I also noticed traces of coolant seeping externally at the seam where the heads mate with the block on the drivers side, not excessive but noticeable. Mainly at the #1 and #5 cylinder below the spark plug. After bringing it to the attention of the engine builder what would cause this leak he just stated to use some head gasket/block sealer. After running about another 1k to 2k miles the leak seemed to disappear with only minimal dripping every so often so I just let it go.

2) To ease my mind I did a radiator pressure test and noticed there wasn't a significant drop in pressure, about a 1-2lb loss in 2 hours so I just let it go. I was also tracking a small to moderate oil leak above the oil filter....removed both oil sensors and resealed the threads....removed the intake manifold and replaced the gaskets and put a nice bead of RTV front and back....long story short, small oil leak stopped!

3) After solving the oil leak I decided to use a head gasket/block
sealer, per the engine builders recommendation, since I was on a roll fixing all the small leaks. Here's where things went south!! I used the blue devil pour-n-go product, added it to the rad per instructions without flushing and removing the thermostat. Wellllll, after mildly driving around for the product to settle in I noticed one heck of a coolant leak now on the passenger side at the #6 cylinder below the spark plug. After driving more at a steady highway speed, 60-70mph it started leaking at the #4 cylinder below the spark plug!!! NEVER leaked coolant at this location(s) until I added the blue devil product!!! Note: Engine runs strong, doesn't miss, no back firing, no steam coming out of the exhaust....

4) Pulled the spark plugs, looks good not wet...oil is clean, no coolant mixing with oil!!! Is coolant leaking through the head bolts? Coolant passages in the vortec heads blocked near the bottom of the spark plug pads? Bad or wrong head gasket installed? Why did it start leaking really bad after adding the gasket/block sealer product? I'm on the verge of replacing the head gaskets but wanted to hear from you guys on what the heck it could be!!!!

FYI...in the pic, the coolant trace from exhaust manifold ports and seam is just the updraft from the main source leak at the head gasket

Thanks in advance!!!!

Signed..."Stumped!!!"

[bd]

The cause sounds like poor workmanship followed by even worse advice....

Normally, I would recommend that you speak to the engine builder.  But, based on his advice to use "block sealer" to correct a cylinder head leak, don't waste your time or trust his/her advice without first verifying it.  However, I would memorialize the repair process and what you discover, using date/time stamped photos.  Include images of the VIN at the beginning and end of the sequence and keep them safe on a dedicated flash drive.

Before you tear anything apart, perform a cylinder leak down test.  Drain and flush the "stop-leak" from the cooling system and then refill completely with potable water.  Attach your radiator pressure tester to the radiator (don't pump it up), start the COLD engine and monitor the rate of pressure rise.  Pressure should increase gradually with temperature over several minutes.  Don't allow the pressure to build beyond 20 PSI.  Document the findings.

At the very least you should plan on new (Felpro) cylinder head gaskets that are recommended by the head manufacturer and new (ARP) cylinder head bolts.  Prepare the gasket sealing surfaces using a hard planer sanding block that is 6" plus in length and ~120-grit emory dipped in solvent.  Wet sand, being careful to just clean the surfaces and not gouge them - you want to remove any superficial gasket residue and leave a planer surface.  Avoid removing metal.  Closely inspect the heads and block sealing surfaces for any evidence of cracks.  Use a precision straight edge and check for head and block flatness.

Chase all of the head bolt holes in the block using a sharp (new) thread tap and oil.  Blow the holes clean of debris using some B-12 followed by moderate pressure compressed air.  [FYI - If you must reuse head bolts, clean the threads using a wire wheel.  NEVER use a thread die to chase head bolt threads!  Because of the harsh environment, it is always better to replace head bolts than risk clamping failure.]  Dry check the fit and alignment of the head gaskets to the heads and block before assembly.  Apply a liberal coat of ARP Thread Sealer to the bolt threads and under the heads of the bolts/washers.  The ARP PTFE enriched sealer doubles as a torquing compound.  Make sure that the ID of washers are chamfered and that the chamfers face "up" toward the bolt heads.  Using a slow steady pull, torque the head bolts in three discrete stages (arbitrarily, 60%, 85% and 100%) following the factory torque sequence.  Torque to 100% a second time through.  Let the engine rest ~24 hours and then recheck the head bolt torque.

[kuhio]

bd...I couldn't agree with you more about the workmanship, yet I always give everyone the benefit of a doubt! I'm just a part time do-it-yourselfer yet I know I could've rebuilt my motor better than the engine builder I chose with some guidance. He was suppose to be one of the reputable builders in the area but I think he had one of his other guys build mine. Oh well, water under the bridge and I'll take care of it my self.

Appreciate the advice and input!