Amatuer

This all started when I blew my first engine. 2002 Mustang gt V8 4.6 16 valve. I looked online and found an engine from a 1998 lincoln mark VIII. Went looked at it and turned the crank all was smooth. Compression test passed. Everything was okay with the engine. So to make this swap happen I had to switch to a 6 bolt flywheel instead of the 8 bolt, I had to rotate the oil pan or else the bottom of the oil pan will touch with the cross member and the engine won’t sit. Got a radiator for the mark viii engine and put it on the mustang. I got all new gaskets. I had the heads resurfaced, I got a new water pump, new thermostat and thermostat housing, any cosmetic is new all fluids new. The only this that I didn’t replace is basically major engine components. ( block, pistons, valves, rockers, springs etc.)
everything seems to be in order and ready for it’s first start up. I turn the key and the engine turns on with no problem. I go for a spin, the power is there the car feels great. Everything about the test drive was great, until....
i get home and coolant is forcing itself out the reservoir Cap. So I go buy a new cap, nothing same problem. I bleed the coolant exactly by the book, bleeder valve. Coolant bleed funnel all that good stuff. Still spits out water, I buy a new reservoir, nothing. I buy a new aftermaker aluminum reservior with a 24psi cap. No fix, I made a direct connection for the fans so they stay on when I turn the key. And nothing. Swapped out all the already new coolant parts with new parts again thinking one was faulty. No avail. I took it to two different local shops and they have no idea what the problem is after spending a couple months in the shops. Coolant does not leak from anywhere else. The oil has no coolant in it.
I really want to fix this thing up because I already had a lot of people telling me I can’t do it or not thinking I’m capable of doing this sort of project. And I’m just too prideful to let them be right.
so please if anyone has any information or anything that can help. It would be greatly appreciated.

houtex

Could be thermostat is bad. Take it out and see if it's the problem.

Could be bad radiator cap. And 24 pounds is *way* too much. Overpressure could be contributing to the cause. Get a 16 pound cap, get it swapped.

Could be a head gasket. Yes, I'm sure you did it right, but still, stranger things. If you start it and see bubbles right away in the radiator, that's a sign.

Could be you have air in the system. The Mark VIII motor had a 'high spot' drain right in front of the alternator, to the car-left of it, on the crossover tube. Highest point in the system. You were to unbolt that bolt and bleed the system from there, not the radiator. Having that air trapped in the block will produce this issue. If you didn't do that. I'm sure you did, right?

And you should have a surge tank, if you don't, connected to that radiator cap area. If the radiator doesn't have an overflow, then yes, you're gonna spit water, because no radiator system doesn't NOT push water out when it gets hot. There's supposed to be a tank, or the system will just shove water out until it's happy.

Water pump could be bad. It happens. Or you could possibly be running it backwards? Nah, nobody does that... (but if you somehow got that belt on a weird way that DOES make it run backwards, I wanna see a pic! )

Think that's it. All I got anyway. I hope it helps. Welcome to the forums! And cool project! Those Mark VIII motors are pretty sweet running things, truth. I know you'll get it figured out.

Amatuer

I checked and replaced the thermostat a few time. Tried different temperature capacities.
I don’t have a radiator cap on my car. I have the reservior tank. So I replaced the plastic reservior thinking it had a tiny hole or crack and got an aluminum one. And tried different psi caps. 24psi is really high. But I just wanted to see if that was the problem which it isnt. I put the 16 psi cap back on.
theres no bubbles in the reservoir tank nor does it gush out when I cold start it. I also did the high spot drain they have infront of the alternator. Also tried different water pumps from different stores (autozone, oriellys, advance auto). Belt is on the way the mark viii diagram has it for.
im going to try a few more head gasket tests. Maybe I just bluntly didn’t do it right? That seams to be my last thing to double check.
unless someway somehow it has to do with something electrical ??

Im at work right now. I’ll upload a picture when I get back to where the car is. Thanks a bunch I appreciate the feedback

Amatuer

The engine bay is really dirty because I had the hood off for a while and I wasn’t working on it and we get some mean monsoons and dust storms in arizona lol

houtex

Show me the thermostat housing? In the above picture, move the camera to the right and take the picture again, maybe angled to the left a little?

Just something that's ticklin' my brain, want to verify. Based on this: https://lmr.com/products/0304-cobra-coolant-hose-guide
But the Mark motor's thermostat housing stuff is different... but not all that much... from the Cobra. Still, maybe that helps.

I've also seen/read/heard/absorbed via psychic powers or something/aliens that you want to lift the front of the car up, so as to ensure the bubbles get out of the engine itself, not just the radiator and hoses. Apparently these 4 cam motors are really bad about trapping air, and that's the fix, beyond continuous burping procedures. Maybe pick the front up on the lowest setting of jack stands or something.

Just a thought: Maybe bypass the heater for now... just to see what happens...?

Your setup is quite nice though! I really want that to work. I'm sending positive vibes your direction!