Is there anything I can diagnose further for this cracked head? My mechanic's not getting back to me and my wife's car is incapacitated as she was just hit so now I'm down to my low compression 4runner and my beater yard F250 with an apparent coolant leak somewhere. I need to get my 4runner working well, and hopefully her subaru back quickly from collision repair.

You could try rechecking cyl compression in number 6. Pull the spark plug out of cyl 4. Listen for air noise there. This might tell you if there is your suspected head gasket compression leak between 4 and 6 which are adjacent on this engine,3400 right? Because cyl 4 intake valves might be open then...Also look for bubbles under the radiator cap. You can borrow/buy a coolant pressure tester and look where the coolant leaks from under radiator pressure(12 psi or what cap says). I put a new head gasket in a 1997 runner 3400 212,000. For a friend. It white smoked like hell and had two shot-glasses of coolant in the #5 cyl. It ran fine after, i was surprised. To save him money(unexpected failure) i did the other gasket 5k later. It now has 253,000 on it. Dealing with the cams(lock bolt), timing tensioner(Stupid location) and exhaust crossover pipe rusty nuts tough... but can be done if you are mechanical and have good tools. hopefully not a cracked head.

I briefly read through your post so bare with me. You did a leak down test and heard a hissing noise through the throttle body which means your intake valve(s) on #6 could be out of adjustment.

If you are not losing coolant and you didn't see any bubble coming out of the radiator when you did the leak down test, your head gasket/head should be fine. The gasket could have failed between the #4 and #6 cylinders, if you remove the spark plug on #4 while pressurizing #6, if there is a leak you should be able to hear/feel air coming out of the spark plug hole (I think?).

You also said you did not see any coolant in the cylinder when you bore scoped it, so that's a good thing but you could still have a bad HG. It should be noted that when I had a bad HG on my 97's original engine, I bore scoped it (cylinder #3 where I was getting the misfire code) the cylinder also looked bone dry and the spark plugs looked the same as the others. I also tried one of those dye tests which came back perfectly normal indicating there was no leak.

When I finally wised up and did a leak down test, the second I pressurized cylinder #3 I saw bubbles coming out of the radiator confirming I did in fact have a bad HG.

I would get a FSM and check the your valve adjustments as already suggested. It could literally be that simple.

I rented the compression tester the first go around. For the leakdown I bought the OTC kit, but then returned it since I was like hey I don't need this. The two seem so similar, cant I just use a leakdown tester for all of it? One tool would be great. Then of course there's radiator compression. Any good idea for a one master kit?

IMO, a leak down tester is a must have for any mechanic (DIY or professional). It takes a lot of the guessing work out of diagnosing a problem. A compression tester (which I have) is ok but only tells you so much. It's a good tool for doing a quick check on the compression of an engine (for instance, you are looking to buy a used car, lawn mower, boat motor etc).

A cooling system pressure tester (I also have one of these) is good for diagnosing leaks in your cooling system but not very effective for determining if you have a HG leak or not.

I think you already narrowed down what your problem is. Unfortunately, the next step is to pull the valve cover and check your valve clearances. I personally haven't done it but I watched Tim's video that he made, technically its for the 4 banger but the concept is exactly the same for the V6. You just need the FSM pages that covers how to check it on the 5VZFE and get yourself some feeler gauges.

If a couple of your intake valves are out of adjustment, you'll need to buy the special tool that holds down the buckets so you can remove the shims. Once you do the math and determine which shims you need, you put the new shims back in and button it back up.

Keep in mind that if your valve clearances are all within spec but you are still loosing compression through an intake valve, the valve itself could be damaged. Unfortunately, that would require much more work.

A compression tester tells you that you have a compression leak. The leakdown tells you where the leak is. That's the difference.

Oh, did anyone mention you need an air compressor to use a leak down tester?

A coolant system pressure test system is a whole other thing. Don't bother with that unless you have a leak. Auto parts stores also often have a kit for rental.

Can I just own a leakdown tester and use that for general compression testing? As long as I don't open the valve to the other gauge it should function the same right? it has the same spark plug hose so I'm assuming it would just "charge" the first gauge with engine cranking