Phew - after a few hour project turned into a 6 day long ordeal, thought I would post some notes to help anyone else taking this on.

First - you need a good amount of tools to do this:

- a scope, not optional. The only way to do this properly without removing the intake manifold
- a pick to remove stuck hoses, and make harness clips easy
- a hose clamp wrench set
- silicone grease
- torx bit for the left intake screw
- a headlamp - also, not optional, it's the only way to see what you're doing
- a lot of rags, you're going to make a mess with coolant

I'm going to assume you've watched the videos, read the diys, etc

Updates and notes:

The first time I did this (sigh - you'll see) I undid a lot of wiring. With the n18, you truly only need to unclip the ECU connections. Everything else can stay in place (apart from those on the intake hoses, of course )

I ordered the bremmen metal housing and the ecs metal crossover pipe from ecs.

Upon disassembly, my factory water pipe was ludicrously stuck in place. I tried to rotate it with a pipe wrench, that just succeeding in ripping pieces of plastic off. The only thing that worked was clamping on some locking pliers, and pulling with an insane amount of force straight out. It took me at least 15 minutes to pull it out. Fortunately, it didn't break!

- you can absolutely sneak your hand behind the water pipe to pull off the clipped in harness connections - my car had 2.

- others have shared this, but the best order here is to insert the water pipe partially, then assemble it with the tstat, and put the clip in with the merged assembly a few inches out.

Now, use your scope to go through the middle intake manifold opening, and aim at the water pump. With it on the screen, it's trivial to maneuver the water pipe in.

Everything was smooth sailing and looked perfect for me, so I buttoned everything back up, filled up the coolant...and it all proceeded to dump straight out on the floor. Wtf?!

With my scope, I was able to see that coolant was pouring out at the block / tstat mating surface. Ok..let's disassemble everything. Everything checked, looked fine, regreased the gasket. Again, coolant poured straight out. Again, wtf

Now I'm desperation mode, I was able to find a locally stocked generic thermostat in plastic. Third time, ripped everything apart again and reassembled with the plastic one.

Lo and behold...something was defective with the bremmen, as it clearly wasn't seating properly, and or had too much preload being applied from the water pipe, because assembly was trivially easy - where the bremmen was proud off the block, the plastic one was nearly flush before even tightening the bolts down.

Don't use the bremmen in combo with the ecs pipe.

- I used a shop vac to do a vacuum bleed, which works incredibly well. Fill up the system, then do a few increments of suction applied to the top of the reservoir. I did about 5 seconds at a time. Refill to get back to max, then repeat until it stabilizes.

- upon my first startup, the car wouldn't get up to temp just idling. I did a quick bleed with the housing screw, but not much air came out, so I think this was just flukey. After a quick drive around the block, temps came up to - in sport mode - circa 200 at normal, tstat opened, and it kicked down to about the normal 180.

- maybe my thermostat was going bad for a while...it wassnt leaking. I replaced it as soon as I had a p0597 (iirc) pop.

My car seems to LOVE something about this...it's running extraordinarily strong. Maybe just the ECU reset? Maybe the fresh coolant - which I have no idea how old it was, since I've only had my car - a 13 r59 w 50k miles - for about 1200 miles.

- the p0597 was ridiculously tenacious - had a really hard time clearing it. Once I did manage to, everything worked swimmingly on the drive.

Hope this helps someone!

 

Since no one responded in 2 months I will, having been there myself. So well done!

I could kinda see where the pipe mated to the water pump from the top so with help located mine that way. I started with a cheap plastic crossover pipe which began leaking after a year so went with the metal one. A bit easier second time around but that clip still flummoxed me. Taking the intake off requires a lot more work so going "through the tunnel" is much more feasible.
I flushed my system with a couple of changes of distilled water before a coolant refill. I used a big plastic pan underneath and managed not to spill too much.

Car Wizard on YouTube pointed out a shoddy new intake manifold on a old LeSaber was the cause of frustrating coolant leak so I suppose it pays to inspect your new parts carefully.

You like the topless life!