Leakdown test Confusion
 

So I have chocolate milkshake in my coolant, not my oil. Been getting worse slowly over time. Nothing seems to be in the oil. Slowly loosing coolant. Needs topping up every week or two. Replaced every coolant line about a month ago after the oilcooler to the head coolant line burst. Running water right now. No smoke out the back - everything behaves normal. Fall is here and I need to get coolant in the engine again. I thought the symptoms were pointing towards the head gasket.

Used a Harbor Freight leakdown tester to help diagnose things. Engine was warm. It took only 15 psi to set the second guage to 0 leakage. More pressure would just make the leakage go negative. I don't get it. It seems arbitrary. Doesn't give me confidence.

All cylinders were low leakage < 5%. All cylinders seemed to have the same piston height. (Used my calibrated stick.) However it seemed that air leakage between 2 & 3 was louder than any of the other combinations. (Tested with a rubber hose into each cylinder.) There was some noise in the oil fill neck, but I'm not sure if it was that significant. No bubbling in the coolant. Hard for me to believe 15 psi would stress anything in an engine.

Should I redo the test with a 100psi tester? What do you recommend? Is this ok?

Any ideas on where the froth on my water is coming from? Time for HG?
Suggestions? Perplexed.

It *could* be head lift. A leakdown won't catch that. What's your boost level?
Can't you just crank the pressure higher? No matter what the gauge says- it's coolant bubbles you want (or rather don't want) to see.

Only 10 psi right now. I've kept it pretty low for a long time now. I want more boost again -- but I have to fix this.

I could crank it higher, but I'd peg the pointer on the leakdown tester. Not sure I want to bend it just yet. 25psi pegs the needle.