Hey guys, long story short, putting my 383 back together after a nightmare of bad luck. It's all good though and I know it comes with the territory. Anyway, I'm checking cooling system with the engine on the stand. I've bolted down the heads and used ARP sealant on the head bolts. I fabricated plates that cover the water pump passages and placed a fitting on them to pressurize the system. The bad news, I think, is it will not hold pressure for very long. It take about 4 minutes to go from 7 psi to 0. The plates are on with gaskets ands RTV (just like I would do with the water pump). All plugs/sensors are installed with sealant. What am I missing? Do the head gaskets need to cycle hot one time to seal off the water passages? Both banks are losing pressure at about the same rate. If I am not mistaken, aren't they independant of each other? Do I need to let the sealant sit overnight or anything like that? Pulling my hair out....... any help is greatly appreciated.

 

As long as you're sure that you sealed it up OK, put some GM sealing tabs in there when you fill the radiator and those will fix any tiny leaks you might have.

 

Do it again but this time use soapy water in a spray bottle to help locate the leaking area. You may also want to pressurize the system with it full of either water or 50/50 mix. Using just air might give you a false sense of leaking. I don't know for sure since I've never pressurized a system using just air.

 

Speedy, I was thinking the same thing. I sprayed around but couldn't find anything which makes me wonder if the head gasket is leaking internally. I think I can fill the bank with water to the top if I tilt the motor with the temp sensor hole being the highest point and fill it up. Just to be sure I covered all my bases, there are 17 bolts, 3 openings in the head, 3 freeze plugs, water pump opening and 1 block drain (or knock sensor) per side. Did I miss any?

 

If you pressurize the system and you think it's leaking past the head gasket. It only has a few places to go right?

So audible traces would be heard either in the cylinder, in the intake or at the dipstick. Not to mention air coming out.

Capish?

Incidentally if the system was full and hooked up like it should, you could find the source much easier. For example looking for bubbles in the coolant by doing a leak down test.

 

True dat Speedy. I filled up the bank with water and pressurized it. I couldn't find the leak at any of the plugs or bolts BUT when I flipped it upside down, water came out of #2 cylinder which is what I suspected (head gasket). I did notice the rate of pressure loss was slowed down a lot. So what is the next step? I am certain the deck is flat and the heads are new from TF. I wonder if the gasket needs to be wet and swell a little to help seat properly or is my luck just bad??? Could it need to be cycled and retorqued? I don't mind swapping out head gaskets if I knew this was not normal. Are cometics any better than the Felpro 1074s that I have on there now?? Should I have used sealer on the water ports on the head gasket? Keep the suggestions coming as I don't want to put this motor in only to have it come right back out. Has anyone done a pressure test on a new motor, dry?

 

Head bolts MUST have sealer on them for sure. Did you?

Do it dry and see if you hear air coming from the plug hole with the plug out.

 

Yup, 34 bolts have ARP thread sealer on the entire length of threaded area. I made sure they were coated good too. I'll press it up and check for air leaking sounds. Just curious why the front hole would leak and no others on the same bank. I didn't check the other bank with water yet until I figured out what the problem is on this bank.

 

Try re torquing in sequence.

 

say what?????? That's way too much sealer!!!!!!

If I remember correctly, a few of those head bolt holes are blind and an accumulation of too much sealer at the bottom of the holes could prevent the bolt from going down into the hole far enough to reach it's full torgue value correctly.

In other words, it gave a false reading on the torgue wrench as it was bottomed out on the sealer.

Re torquing the bolts might take care of that, if that was the problem.

Just a thought.

 

I tried to retorque them with no joy. I ordered a set of cometics and will put those on and redo the pressure test. I'd find it hard to believe that I put the heads on wrong or have an issue with my heads/deck. I've never had any problems in the past doing SBC heads but you never know. Is there anything special with cometics that I need to be aware of or just install them like i did the felpros?

 

Cometics are going to be more finiky to seal up than the Felpros. They have a published smooth finish that is needed on the heads and deck. Also, it is good to retorque them after a heat cycle.

 

Hmm, could my problem not be a real problem? Do the felpros just need a heat cycle and retorqued? I just want to avoid doing head gaskets with the engine in the car and without a test stand, its gonna be tough to heat cycle out of the car

 

No - you don't have to retorque the replacement gaskets. If you get any seepage, use the sealing tabs like I previously mentioned. There's a reason GM puts them in the engines, and I have always used either those or some other sealer on a new engine.