rebuilt/unfired SB. intergrity of the cooling system. how much loss of psi is acceptable (if any). I'm thinking if it is pumped up to 15 lbs it should stay there (or very very close). Your thoughts please

Yes it should hold pressure for quite a while. If it leaks out in less than a hour to nothing then you have a leak that will seep water.

Thanks bro, I was afraid of that, alright I'll dig back into it, again

Check your pressure checker on a known good cooling system first, many testers leak over time.
Doug

Yes my Stant pump up kit is a bit leaky but on this I drilled/tapped the stat housing extension for a brass schrader valve & pumped it up directly with an air hose/chuck from the compressor. What I am really after is to find out if it is the head gasket(s) or the intake gasket(s) so if it is the intake gaskets (whichever side) then I dont have to pull the heads

Is it full of coolant? If not and you are just using air you could use a soap and water mix and spray it on the possible leak areas and look for bubbles. Tire leak check could also work.

No coolant cuz I know I have a problem. I've used dish soap/water on the outside to check for bubbles but the inside is where I am focused now. What is "tire check", cuz if that is something that will show up on the outside like smoke or a dye & not need to be cleaned out then that sounds like exactly what I need

Tire check is a liquid mixed with water. It really bubbles when there is a leak. It can leave a residue. How can you see the underside of the small block intake coolant passages?

Yeah I would not want to introduce water into there. To ans your Q accessing the block dist hole would let me checkout the (2) rearmost cooling passages between head/intake. A shop here has a smoke machine that pumps it in to 5 psi he said & it'd be 1/2 hr shop time ($40). I might just bite the bullet & replace both head/intake gaskets & if that dont do it then the tcover gasket.

I have to ask. What made you check this in the first place? Was there a previous coolant leaking problem before the fresh rebuild? Did you deck the block and cut the heads hard and not cut the intake face on the head. Are the heater lines connected or just looped back to themselves? Some more info could help...

It should hold pressure a long time. I tested a big block that was losing coolant. Tested cold, it held pressure for 12 hours overnight. 16 psi and didn't bleed off a single pound. When hot though, it leaked coolant into the chamber and sent it out the pipe as steam.

If you can't maintain ANY pressure, definitely need to dig deeper

BP I did Sanborns' cooling mods drilled more/larger holes in block/heads/gaskets and I had to have machined 3/16 alum spacers so the intake would line up with the bolt holes in those chinese fake EQ heads that that crook Ben Gorman of "Promax" in indianapolis sold me. something told me to be proactive & pump it up & I think some of the holes I redrilled/added were a bit too close to the bolt holes and or fire ring not sure on that, nothing obviously fubared but some I cut it a bit too close. My birthday is tomorrow (64) & some birthday money came in the mail today so I am going to rent a hooker (yes I will watch for adams apples/police stings, thanks guys for the heads up on that for last b day, you guys have my back ) and order some new head/intake gaskets & start over & be a bit more meticulous (I'm OCD as it is but I have to take it to a new level on this rare leaker that has baffled me. 70cuda aggreed it should not be leaking down more than a fraction of a lb to my way of thinking. Thanks guys

Their cheaper than a wife and they never get fat...

Yes my intake gaskets & one head gasket (I already have a spare new one) will be in tomorrow (Tues) morning .

Robert...She's not getting paid for her actions...She's paid to leave....

She got paid for her actions & even tho she was expected to leave actually I was (sorry) to see her leave. Right now everything is good in the 'hood . Tomorrow the heads/intake will be coming (back) off for the third time